Jun 24, 2018 - GNSS: Global Navigation Satellite Systems. GPS: Global Positioning System. GSD: Global Systems Division. HARN: High Accuracy Reference ...
PRECISE MEASUREMENT OF CONTINUOUSLY OPERATING REFERENCE STATION (CORS) SITE DEVIATION DUE TO SEISMIC ACTIVITIES AND HORIZONTAL TIME DEPENDENT POSITIONING (HTDP) SOFTWARE PERFORMANCE ANALYSIS
A thesis submitted to the Institute of Space Technology for partial fulfilment of the requirements for the degree of Master of Science in Global Navigation Satellite System
by Zeeshan Haider Hashmi
Supervisor Dr. Umar Iqbal Bhatti
Department of Aeronautics and Astronautics Institute of Space Technology Islamabad August 2017
Institute of Space Technology Islamabad Department of Aeronautics and Astronautics
Precise Measurement of Continuously Operating Reference Station (CORS) Site Deviation Due to Seismic Activities and Horizontal Time Dependent Positioning (HTDP) Software Performance Analysis
by Zeeshan Haider Hashmi APPROVAL BY BOARD OF EXAMINERS
Dr. Umar Iqbal Bhatti (Supervisor)
Dr.Najam Abbas (Internal Examiner)
Dr. Muhammad Ushaq (External Examiner)
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AUTHOR’S DECLARATION I take full responsibility of the research work conducted during the MS Thesis, titled ―Precise Measurement of Continuously Operating Reference Station (CORS) Site Deviation Due to Seismic Activities and Horizontal Time Dependent Positioning (HTDP) Software Performance Analysis‖. I solemnly declare that the research and development work presented in the MS Thesis is done solely by me with no significant help from any other person; however, small help wherever taken is duly acknowledged. I have also written the complete thesis by myself. Moreover, I have not presented this thesis (or substantially similar research and development work) or any part of the thesis previously to any other degree awarding institution within Pakistan or abroad. I understand that the management of IST has a zero tolerance policy towards plagiarism. Therefore, I as an author of the above-mentioned thesis, solemnly declare that no portion of my thesis has been plagiarized and any material used in the thesis from other sources is properly referenced. Moreover, the thesis does not contain any literal citing (verbatim) of more than 70 words (total) even by giving a reference unless I have obtained the written permission of the publisher to do so. Furthermore, the work presented in the thesis is my own original work and I have positively cited the related work of the other researchers by clearly differentiating my work from their relevant work. I further understand that if I am found guilty of any form of plagiarism in my thesis work even after my graduation, the Institute reserves the right to revoke my MS degree. Moreover, the Institute will also have the right to publish my name on its website that keeps a record of the students who plagiarized in their thesis work. ________________ Zeeshan Haider Batch-Roll # 150511021 I hereby acknowledge that submitted thesis / report / paper is final version and should be scrutinized for plagiarism as per IST policy.
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Copyright@2016 This document is jointly copyrighted by the author and Institute of Space Technology (IST). Both IST and the author can use, publish or reproduce this document in any form. Under the copyright law no part of this document can be reproduced by anyone, except the copyright holders, without the permission of the author.
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ACKNOWLEDGEMENTS I would like to thanks Almighty ALLAH for His countless blessings for giving me wisdom and guidance in completing my research work. I acknowledge all the support/ guidance of my thesis supervisor Dr. Umar Iqbal Bhatti of the Department of Aeronautics and Astronautics at Institute of Space Technology Islamabad. The door to Dr. Umar office was always open whenever I ran into a trouble spot or had a question about my research or writing. He consistently allowed this paper to be my own work, but steered me in the right the direction whenever he thought I needed it. I would like to thanks Dr. Najam Abbas Naqvi of the Department of Aeronautics and Astronautics at Institute of Space Technology Islamabad. Without the guidance and inspiration of Dr. Najam Abbas I would not have achieve success in my thesis. A special thanks to Dr. Muhammad Ushaq for giving his valuable inputs and suggestions during my course of work.
Finally, I must express my very profound gratitude to my parents and to my wife and son Muhammad for providing me with unfailing support and continuous encouragement throughout my years of study and through the process of researching and writing this thesis. This accomplishment would not have been possible without them. Thank you.
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ABSTRACT The NGS CORS sites deviate from their assigned position coordinates due to seismic activities. A rigorous computation is required to maintain position coordinates of NGS CORS network. On 23rd of June 2014 an earthquake of magnitude 7.9 strongly hit the Aleutian Islands. This earthquake deviated Adak AB21 CORS site from its assigned NAD_83 (EPOCH 2010) position coordinates. NGS revised position of this CORS site last time in December 2012 by using 57 days of data. As the position coordinates of this CORS site are not revised after 2012, the present GPS data recorded shows a significant deviation of this CORS site from published position coordinates. This substantial deviation is due to Aleutian Islands earthquake and the North American tectonic plate movement. In this thesis précised computations of all inter seismic, co seismic, post seismic activities and North American tectonic plate movement are achieved to revise Adak AB21 CORS position coordinates. The HTDP software is a service that permits users to convert positional coordinates across time and between different spatial reference frames. The Last earthquake dislocation model (3rd November 2002 Denali earthquake) incorporated into HTDP software was developed in 2013. This model was developed by Dr. Jeffery freymuller of the University of Alaska. The present version of HTDP software includes a post seismic motion model only for Denali earthquake of 7.9 magnitudes that hit Central Alaska on 3rd of November 2002. The most recent modification of Horizontal Time Dependent Positioning software version 3.2.5 has been done on August, 30 2015. It only modifies corrections for minor rounding error inconsistencies. The recent HTDP 3.2.5 software version model does not include position coordinates variations due to 23rd June 2014 Aleutian Islands earthquake. In this research work the HTDP software measurements are updated with the help of AB21 CORS site observation data. This updating of Horizontal Time Dependent Positioning (HTDP) software measurements will include all crustal displacements due to seismic activities associated with 23rd June 2014 earthquake. The novel contributions of this thesis are: a performance analysis of AB21 CORS site and ADK IU accelerometer for the precise measurement of 23rd June 2014 Aleutian Islands earthquake, the deviation of AB21 CORS site associated with Aleutian Islands earthquake and North American tectonic movement is precisely measured by using CORS data. This paper also includes the revision of AB21 CORS site position coordinates including all deviations associated with inter seismic, co seismic, post seismic activities and North American tectonic plate movement and the revised AB21 CORS site position coordinates are used to update HTDP software measurements. xvi
Table of Contents Ser No. Title
Page No.
Approval
ii
Author‘s Declaration
iii
Copyright
v
Acknowledgement
vi
Abstract
vii
Table of Contents
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List of figures
xi
List of Tables
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List of Abbreviations
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Contents 01
INTRODUCTION .............................................................................................................................. 1
1.1
Literature Review.................................................................................................................... 1
1.2
Research Background.............................................................................................................. 8
1.3
Research Motivations and Objectives .................................................................................. 10
1.4
Statement Of Need ............................................................................................................... 11
1.5
Rudiments of Research Methodology .................................................................................. 12
1.6
Thesis Layout......................................................................................................................... 13
02 NATIONAL GEODETIC SURVEY (NGS) CORS NETWORK .................................................................. 16 2.1
Introduction .......................................................................................................................... 16
2.2
CORS And The Definition Of The NSRS.................................................................................. 20
2.3
Data Archives ........................................................................................................................ 23
2.4
UFCORS and OPUS ................................................................................................................ 23
2.5
CORS Applications ................................................................................................................. 25
2.6
Multipath Studies.................................................................................................................. 25
2.7
Crustal Motion ...................................................................................................................... 26
2.8
Sea Level Changes ................................................................................................................. 27
2.9
Tropospheric Studies ............................................................................................................ 28
2.10
Ionospheric Studies ............................................................................................................... 29
2.11
Geo Location Of Aerial Moving Platforms ............................................................................ 30
2.12
The Future of NGS CORS Network ........................................................................................ 30
03
HORIZONTAL TIME DEPENDENT POSITIONING (HTDP) SOFTWARE ......................................... 33 xvii
3.1
Introduction .......................................................................................................................... 33
3.2
Estimating Horizontal Crustal Velocities ............................................................................... 33
3.3
Estimating Crustal Displacements......................................................................................... 36
3.4
Updating Positional Coordinates .......................................................................................... 38
3.5
Transforming Positional Coordinates ................................................................................... 39
3.7
Transforming Velocity Vectors .............................................................................................. 45
3.8
Reference Frames Recognized By HTDP ............................................................................... 46
3.9
Software Characteristics ...................................................................................................... 49
04
Research of Geodetic Datum .................................................................................................... 51
4.1
Introduction ......................................................................................................................... 51
4.2
Explaining a Reference System ............................................................................................. 51
4.3
The Evolution of NAD 83 ....................................................................................................... 54
4.4
GPS revolution ...................................................................................................................... 55
4.5
NAD 83 3rd Realisation Included CORS .................................................................................. 57
4.6
The Development of ITRS...................................................................................................... 61
4.7
Transforming Between Reference Frames ........................................................................... 63
05
RESULT ANALYSIS OF SEISMIC DEVIATIONS .............................................................................. 65
5.1
Introduction: ........................................................................................................................ 65
5.2 Performance Analysis of AB21 CORS Site and IU ADK Station for Precise Earthquake Measurement.................................................................................................................................... 68 5.2.1
Earthquake data recorded by AB21 CORS site .............................................................. 68
5.2.2
Variations In AB21 CORS Site Position .......................................................................... 69
5.2.3
Variations In AB21 CORS Site Velocity .......................................................................... 70
5.2.4
Earthquake data recorded by IU ADK Accelerometer .................................................. 72
5.2.5
Earthquake Displacement Variations Recorded By ADK IU Accelerometer ................. 72
5.2.5 a
Displacement variations in East – West axis ................................................................ 73
5.2.5. b
Displacement variations in South-North axis............................................................ 73
5.2.5. c
Displacement variations in Up – Down axis .................................................................. 74
5.2.6
Earthquake Velocity Variations Recorded By ADK IU Accelerometer .......................... 74
5.2.6. a
Velocity variations in East – West axis .......................................................................... 74
5.2.6. b
Velocity variations in South – North axis .................................................................. 75
5.2.6. c
Velocity variations in Up – Down axis ........................................................................... 75
5.3 Precise Measurement of AB21 CORS Site Deviation From Assigned Coordinates Due To Aleutian Islands Earthquake ............................................................................................................. 76 5.3.1
60 Days post seismic data recorded by AB21 CORS Site............................................... 76
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5.3.2
Monitoring of AB21 CORS Site Deviation Along x-axis ................................................. 77
5.3.3
Monitoring of AB21 CORS Site Deviation Along y-axis ................................................. 80
5.3.4
Monitoring of AB21 CORS Site Deviation Along z-axis.................................................. 83
5.4
AB21 CORS Site Deviation Due to Tectonic Motion (2006-2016) ......................................... 86
5.4.1
Monitoring of AB21 CORS site deviation along x-axis .................................................. 86
5.4.2
Monitoring of AB21 CORS Site Deviation Along y-axis ................................................. 89
5.4.3
Monitoring of AB21 CORS Site Along z-axis .................................................................. 91
5.5
Performance Analysis of HTDP Software with AB21 CORS Data of Year 2014 ..................... 94
5.5.1
HTDP software and AB21 CORS site measurements along x-axis ................................. 94
5.5.2
HTDP software and AB21 CORS Site measurements along y-axis ................................ 97
5.5.3
HTDP software and AB21 CORS Site measurements along z-axis............................... 100
5.6
Revised Position Coordinates of HTDP Software and AB 21 CORS Site (2012-2016) ......... 103
5.6.1
Updated x-axis position coordinates .......................................................................... 104
5.6.2
Updated y-axis position coordinate ............................................................................ 110
5.6.3
Updated z-axis position coordinates........................................................................... 116
06
CONCLUSION AND RECOMMENDATIONS FOR FUTURE WORK .............................................. 122
6.1
Conclusions ......................................................................................................................... 122
6.1.1
Precise assessment of Aleutian Islands earthquake ................................................... 122
6.1.2
Rigorous measurement of AB21 CORS site deviation after the earthquake .............. 122
6.1.3
Deviation of Adak AB21 site due to North American Plate movement ...................... 123
6.1.4
Performance analysis of Horizontal Time Positioning (HTDP) Software .................... 123
6.1.5
Revision of AB21 CORS site Position Coordinates ...................................................... 123
6.2
Recommendations For Future Work .................................................................................. 123
Certificate........................................................................................................................................ 125 References ...................................................................................................................................... 126
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List of Figures Figure 1.1 General Plate motions on a global scale. Regional maps show far more complicated motion vectors. Length of arrows indicates rate of movement of that part of the plate..................................... 5 Figure 1.2 Plate velocities from Plate Boundary Observatory (PBO) ..................................................... 6 Figure 2.1 The NGS CORS site map .................................................................................................... 20 Figure 2.2 More than 280 CORS sites in Cascadia are part of the US plate boundary observatory (PBO). ................................................................................................................................................... 20 Figure 2.3 depicts the working of OPUS ............................................................................................... 25 Figure 2.4 a CORS site antenna surrounded by buildings inside the city ............................................. 26 Figure 2.5 depicts the deviations of NGS CORS sites due to seismic activities ................................... 30 Figure 3.1 The velocity model of North American tectonic plate. ........................................................ 46 Figure 3.2 represents the velocity model of East and West CONUS .................................................... 46 Figure 4.1 shows the earth geodetic ellipsoid parameters ..................................................................... 53 Figure 4.2 Combined tracking DoD network that defines WGS 84 ...................................................... 61 Figure 4.3 Sites defining ITRF96 .......................................................................................................... 62 Figure 5.1 The Deviations (m) of AB21 CORS site from its assigned position coordinates ................ 69 Figure 5.2 the velocity (m/s) variations of Adak AB21 CORS site ...................................................... 70 Figure 5.3.a,b,c,d The AB21 CORS site deviations during 24hr of 23rd June 2014.............................. 71 Figure 5.4 Aleutian Islands earthquake displacement variations in east-west direction ....................... 73 Figure 5.5. Aleutian Islands earthquake displacement variations in south-north direction................... 73 Figure 5.6 Aleutian Islands earthquake displacement variations in up-down direction ........................ 74 Figure 5.7 Aleutian Islands earthquake velocity variations in east-west direction ............................... 80 Figure 5.8 Aleutian Islands earthquake velocity variations in south-north direction ............................ 80 Figure 5.9 Aleutian Islands earthquake velocity variations in up-down direction ................................ 81 Figure 5.10 AB21 CORS site post seismic measurements along x-axis ............................................... 85 Figure 5.11 AB21 CORS site post seismic measurements along y-axis ............................................... 83 Figure 5.12 AB21 CORS site post seismic measurements along z-axis ............................................... 91 Figure 5.13 AB21 CORS site deviation due to tectonic plate movement along x-axis......................... 94 Figure 5.14 AB21 CORS site deviation due to tectonic plate movement along y-axis......................... 95 Figure 5.15 AB21 CORS site deviation due to tectonic plate movement along z-axis ......................... 99 Figure 5.16 AB21 CORS site deviation along x-axis during year 2014 ............................................. 101 Figure 5.17 HTDP software measurements along x-axis during year 2014 ........................................ 102 Figure 5.18 the comparison between AB21 CORS site and HTDP deviation along x-axis during year 2014 .................................................................................................................................................... 102 Figure 5.19 AB21 CORS site deviation along Y-axis during year 2014 ............................................ 104 Figure 5.20 HTDP software measurements along y-axis during year 2014 ........................................ 100 Figure 5.21 comparison between AB21 CORS site and HTDP deviation along y-axis during year 2014 ............................................................................................................................................................ 100 Figure 5.22 AB21 CORS site deviation along z-axis during year 2014.............................................. 102 Figure 5.23 HTDP software measurements along z-axis during year 2014 ........................................ 103 Figure 5.24 comparison between AB21 CORS site and HTDP deviations along z-axis during year 2014 .................................................................................................................................................... 103 Figure 5.25 updated deviations of HTDP along x-axis (2012-2016) .................................................. 109 Figure 5.26 AB21 CORS site deviations along x-axis (2012-2016) ................................................... 109 xi
Figure 5.27 updated HTDP software measurements with AB21 CORS site deviations along x-axis 110 Figure 5.28 updated deviations of HTDP along y-axis (2012-2016) .................................................. 115 Figure 5.29 AB21 CORS site deviations along y-axis (2012-2016) ................................................... 115 Figure 5.30 updated HTDP software measurements with AB21 CORS site deviations along y-axis 116 Figure 5.31 updated deviations of HTDP along z-axis (2012-2016) .................................................. 120 Figure 5.32 AB21 CORS site deviations along z-axis (2012-2016) ................................................... 121 Figure 5.33 updated HTDP software measurements with AB21 CORS site deviations along z-axis. 121
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List of Tables No table of figures entries found.Abbreviations ANSS: Advanced National Seismic System ARP: Antenna Reference Point ASCII: American Standard Code for Information Interchange CESMD: Centre for Engineering Strong Motion Data CGS: California Geological Survey CIGNET: Cooperative International GPS Network CONUS: Conterminous United States CORS: Continuously Operating Reference Station CORSAGE: CORS Amiable Geographic Environment DGPS: Differential GPS DORIS: Doppler Orbitography and Radio positioning Integrated by Satellite ECEF: Earth Centered Earth Fixed ESRL: Earth Systems Research Laboratory FAA: Federal Aviation Administration GIA: Glacial Isostatic Adjustment GIS: Geographical Information System GNSS: Global Navigation Satellite Systems GPS: Global Positioning System GSD: Global Systems Division HARN: High Accuracy Reference Network HTDP: Horizontal Time Dependent Positioning IERS: International Earth Rotation Service IGS: International GNSS Service ITRF: International Terrestrial Reference Frame ITRS: International Terrestrial Reference System JPL: Jet Propulsion Laboratory KML FILE: Keyhole Markup Language File MYCS: Multi-Year CORS Solution xiv
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NAD 83: North American Datum 1983 NASA: National Aeronautics and Space Administration NDGPS: Nationwide Differential GPS system NGA: National Geospatial-Intelligence Agency NGS: National Geodetic Survey NIMA: National Imagery and Mapping Agency NNSS: Navy Navigation Satellite System NOAA: National Oceanic and Atmospheric Administration NSRS: National Spatial Reference System OPUS: Online Positioning User Service OPUS-RS: Rapid static PBO: Plate Boundary Observatory PPP: Precise Point Positioning PPS: Precise Positioning Service REVEL: Recent Velocity RINEX: Receiver Independent Exchange Format RTCM: Radio Technical Commission for Maritime Service RTK: Real-Time Kinematic SDBM: Shallow Drilled Braced Monument SLR: Satellite Laser Ranging SWPC: Space Weather Prediction Centre TEC: Total Electron Content UFCORS: User Friendly CORS UNAVCO: University NAVSTAR Consortium USCG: United States Coast Guard Us-DoD: United States of America Department of Defence USGS: US Geological Survey VLBI: Long Baseline Interferometry WAAS: Wide Area Augmentation System WGS: World Geodetic System
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01 1.1
INTRODUCTION
Literature Review The National Geodetic Survey (NGS) describes and deals with the National Spatial
Reference System (NSRS) in the United States of America. The definitions of longitude, latitude, and height (and other geodetic parameters), described by the NSRS offers a versatile, position coordinate based foundation that assists the wide range of today‘s threedimensional navigating applications. The NGS was established on February 10, 1807 earlier known as Survey of Coast and later the Coast and Geodetic Survey. During most of the two hundred years development of the National Spatial Reference System, availability to the system has been offered by a system of inert, constructed ground control points. These geodetic control sites have computed horizontal and/or height position coordinates estimated by in practice optical and mechanical surveying methods and geodetic calculations. However ground control points are still in practice nowadays, the modification and availability to the NSRS has been spectacularly modernized with the development of the Global Positioning System (GPS). The development of more accurate geodetic control has been established progressively with the utilization of GPS in mid-1980s. Today, surveying industry is totally dependent on GPS and traditional horizontal-positioning methods and equipment are rarely used. Since 1994, NGS has controlled the growth and process of a various association system of lastingly installed, GPS reference stations, recognized as continuously operating reference stations (CORS). The CORS network assists centimetre level precision along three axes GPS positioning and other GPS-based applications in the United States of America and its territories, and also in some associating overseas countries. Also, this network symbolizes an updated means for researchers and others to dynamically utilize the NSRS by means of calculated station position coordinates and velocities, and GPS observational data files, obtainable free of cost, for post processed GPS applications. In 2001, NGS added the working and assessment of the CORS system by establishing a connected Web-based service, the Online Positioning User Service (OPUS), to offer a computerized process of finding user positions comparative to the CORS network. OPUS offers quick, precise, dependable, and steady availability to the NSRS by means of an easy Web interface. OPUS needs a user to just gather dual-frequency GPS data at a site whose position coordinates are required, and then upload the observation data file to the utility. In few minutes, the user 1
will receive an email having the OPUS-derived position coordinates for the entered GPS observation data file. As the essential technology of GPS has enhanced with the passage of time, CORS and OPUS have both developed and advanced as well. The CORS network started with NGS‘ early 1994 system of a stable GPS sites on the Gaithersburg, MD, campus of today‘s National Institute of Standards and Technology – a suitable location for the nascence of what has progressed into the de facto national positioning infrastructure standard. In 1994, the CORS network had developed selfeffacingly to a total of five sites, situated throughout the country. The system‘s expansion has accelerated significantly with the period of time and in 2005 more than 200 additional CORS stations were included into the network. The program carries on relying on various associations with other institutes to help understand the goal to structure a national, versatile, and vigorous reference station network. In 2006 NGS owned and operated less than three percent of the CORS stations. The mainstream of the stations were established by a variety of local, state, and federal government organizations, educational institutes, and the confidential division. CORS associating institutes, now numbering nearly 200, set up lasting reference stations to prop up their personal diverse needs and purposes – real-time navigation surveying and mapping, atmospheric modelling, and geophysical research to name a number of common uses. By contributing in the CORS network, these stations partners can understand a lot of additional straight advantages to their GPS programs – containing data quality control, sharing, and storage functions[1]. There are numerous CORS system partners though some of the contributing programs and institutes will be mentioned, due to the level of participations they are building to the program. First, the United States National Science Foundation has supported a determined, multi-year study work – Earth Scope– with objectives expected at increasing our comprehension of the practical procedures engaged in the arrangement and development of North America. One component of Earth Scope, the Plate Boundary Observatory (PBO), is planned to be a geodetic observatory determined on studying the inter-tectonic plate, deformation-produced strain field in the western United States. A critical monitoring tool of PBO is a system of continuous GPS stations that will ultimately rise to nearly 900 installations. Most of these PBO stations have already been included into the CORS set-up, with additional to go after, as they are mounted. Some other organizations in the geophysical research society have recognized local GPS systems to check earth crustal displacement produced movements – works that are comparable to PBO‘s comprehension, however on more regional levels. Second, NOAA‘s Global Systems Division (GSD) has 2
mounted dozens of GPS CORS stations. Most of these are located with meteorological observing equipment, and they contribute in a countrywide system of almost 400 stations, utilized to find out atmospheric moisture content [2]. Third, the United States Coast Guard and Department of Transportation are operational jointly to enhance the Coast Guard‘s active real-time GPS maritime navigational beacon structure to give countrywide differential GPS signal coverage, in hold of secure and well-organized global navigation. CORS Stations in this Nationwide Differential GPS (NDGPS) system, now numbering almost one hundred, will give out two operations by also contributing in the CORS system. Fourth, the Federal Aviation Administration‘s (FAA) Wide Area Augmentation System (WAAS) is a satellite-based, real time error correction system, planned for airliner navigation, and however is commonly used in terrestrial based applications. Every ground reference stations of the WAAS system are also supplying data into the CORS network. Fifth, the National Aeronautics and Space Administration (NASA) have been developing permanent GPS systems for several years. Most of these stations, worked for a variety of space based applications and research work, have been included into the CORS system[3]. At last, numerous state governments, like North Carolina, Florida, Michigan, Texas, and Ohio Oklahoma (each at present has nearly 20 or more stations), have developed region-wide or large-region GPS set ups to maintain their own positioning applications, either real-time or post-processed. These region wide works are usually the operation of the state‘s department of transportation (excluding the North Carolina Geodetic Survey) and lots of also add to the CORS set-up. A number of other states are at present in the establishing phases of constructing their own comparable state-wide GPS based network. Scientists at the moment have a quite excellent knowledge of how the tectonic plates displace and how such deviations associate to earthquakes and any seismic activity. Deviation is mainly marked beside narrow zones between tectonic plates where the impacts of plate-tectonic forces are most obvious At present the tectonic plate motion can be tracked precisely by means of space based geodetic calculations; geodesy is the science of the size and shape of the Earth. As the tectonic plate movements are global in level, they are precisely calculated by satellite-based techniques[4]. In 1970s witnessed the fast development of space geodesy, a word useful to spacebased methods for estimating accurate, frequent calculations of cautiously selected points on the Earth‘s surface gaped by hundreds to thousands of kilometres. The Global Positioning System (GPS) has been the most practical for researching the Earth‘s crustal deviations. By frequently calculating displacements between particular points, scientists can 3
conclude the displacement along fault lines or between tectonic plates. The distances between GPS stations are previously being calculated frequently in the region of the Pacific basin. By observing the impacts between the Pacific tectonic Plate and the nearby mainly continental tectonic plates, scientists are working more about activities that erect up to seismic activities and volcanic eruptions in the circum-Pacific ―Ring of Fire‖. Spacegeodetic information have previously established that the rates and directions of tectonic plate deviations, averaged over a number of years, evaluate well with velocities and directions of plate deviations averaged over millions of years.
Figure1.1 General Plate motions on a global scale. Regional maps show far more complicated motion vectors. Length of arrows indicates rate of movement of that part of the plate. Two lines of proof opened the secrecy: apparently connected rock types great space apart and the magnetic polarity evidenced by ocean-floor rocks. Alfred Wegener (18801930) discovered that major geological types on separated continental lands frequently corresponding very closely when the continents were brought together. For example, the Appalachian Mountains of eastern North America similar with the Scottish Highlands, and the characteristic rock strata of the Karroo system of South Africa were matching to those of the Santa Catarina system in Brazil. He was hated for his idea of ―continental drift‖ because the famous geology of ocean basins that corroborate tectonic plate and continental drift was not adequately known until the 1960s and 70s. Evidence of previous velocities of tectonic plate deviation on a lesser extent can be attained from geologic mapping. If a rock structure of known era—with characteristic composition, arrangement, or remnants—mapped on one plane of a tectonic plate border can be coordinated with the similar configuration on the 4
other surface of the border, then estimating the space that the configuration has been compensated and can provide an approximation of the standard velocity of tectonic plate movement. This easy but efficient method has been utilized to find the velocities of tectonic plate movement at deviating boundaries, for example the Mid-Atlantic Ridge, and changing boundaries, such as the San Andreas Fault line. The oceans bottom was an important point to the mystery. As the ocean-ground magnetic striping archives the flip-flops in the Earth‘s magnetic field strength, scientists, determining the periods of magnetic reversals, can compute the standard velocity of tectonic plate motion over time periods of numerous million years. These mean velocities of tectonic plate gaps can range broadly. The Arctic Ridge has the minimum velocity (less than 2.5 cm/yr), and the East Pacific Rise near Easter Island, in the South Pacific about 3,400 km west of Chile, has the maximum velocity (more than 15centimetre per year)
Figure 1.2 Plate velocities from Plate Boundary Observatory (PBO)
Since April 17, 2011, the NGS and the other research Centres of the International GNSS Service (IGS) have been offering GPS satellite orbits data (ephemerides) that are mentioned to a recent terrestrial reference frame, known as IGS08 and explained by the IGS. This new reference frame is depended on GPS observations data and was planned to be steady with the International Terrestrial Reference Frame of 2008 (ITRF). ITRF2008 is the frame realization of the International Earth Rotation and Reference Systems Service (IERS) and is space based geodetic method explanation, joining ―Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Doppler Orbitography and Radio positioning 5
Integrated by Satellite (DORIS) and GPS data‖. While, the most appropriate Helmert transformation between IGS08 and ITRF2008 realisations for a set of developed, worldwide GNSS satellite tracking stations is the individuality task, the transformed ITRF2008 locations have a site precise "correction" useful to them to produce IGS08 locations. (Thus the IGS08 location for a specific station might be different from its equivalent ITRF2008 location; but, the rates stay equal. By means of IGS08 position coordinates and the connected absolute antenna calibrations in system with IGS satellite orbits a steady reference frame is realized. Furthermore, NGS has modified the IGS satellite orbits from January 1, 1994 to April 16, 2011 in its online storage with the published IGS reprocessed (repro1) orbits that are all associated constantly with IGS05. For mainly non-research purposes, users can conveniently combine IGS05 and IGS08 orbits to calculate position coordinates for control points. On 7 October 2012, the IGS initiated an update to IGS08 and is known as I Gb08. This modification is unseen to majority users as it purposeful on initiating positions for: 3 new CORS stations at versatile method collocations and 33 IGS reference frame stations with IGS08 position coordinates cancelled by positional glitches. Position coordinates for CORS stations with rate glitches were not modified. On September 6, 2011, NGS revised the National Spatial Reference System NAD 83 (CORS96, MARP00, PACP00) coordinate positions and displacement rates for all CORS stations, to NAD 83 (2011, MA11, PA11). The NAD 83 (2011) reference frame, which is comparative to the fixed North American tectonic plate, is utilized to describe the position coordinates for stations situated in the Conterminous United States (CONUS), Alaska and US lands in the Caribbean. The NAD 83 (MA11) reference frame is developed with respect to the fixed Marianas tectonic plate and is utilized to describe position coordinates in the land of Marianas. The NAD 83 (PA11) is a Pacific tectonic plate fixed reference frame and is utilized to describe position coordinates in the area of Hawaii, the Marshall Islands, American Samoa and other US lands located on the Pacific tectonic Plate. The recent realization of NAD 83 reference frame includes no datum variation, that defines, the source, extent and orientation of NAD 83(2011) are alike to those of NAD 83(CORS96) reference frame, and similar for the two other reference frames. The position coordinates are not the identical in the previous and latest realizations for several aspects counting the exchange to absolute antenna calibrations, latest/updated processing algorithms, and better glitch detection, a number of years of extra GPS data, modify in reference epoch, and an enhanced description of the global reference
6
frame, IGS08[5]. In a few words, the two major modifications are sourced by the variation in reference epoch and the shift from comparative to absolute antenna calibrations. This reference epoch has transformed by eight years from 2002.00 to 2010.00 time period. The assigned NAD 83 position coordinates match to the location of the site at January 1 2010 (or equally, epoch 2010.00), and if a location at a diverse time is necessary then the adopted rates must be functional and a new location calculated. In case of using a latest reference epoch, systematic inaccuracies that happen when points are situated comparative to CORS without implementing to them suitable station displacement rates are decreased. This present reference epoch date will particularly profit those concerned in positioning events in lands of dynamic crustal deviations, e.g. western CONUS and Alaska. Professionals should receive particular note that CORS sites position coordinates assigned in IGS08 and NAD83(2011, MA11, PA11) realizations are different with respect to those adopted in ITRF00 and NAD 83(CORS96, MARP00, PACP00) in the utilization of a dissimilar set of antenna calibrations. In previous time users of CORS position coordinates just required to make sure they were applying the calibration for the antenna and radome pair they obtained their data with, as calibrations were produced by means of comparative methods. With the introduction of ITRF2008 and IGS08 realizations, an entirely unique complete calibration method was utilized to produce antenna calibrations. In addition as the absolute antenna calibrations also contain calibrations for satellite antennas and also for ground position antennas they are adjusted regularly and are described for a specific reference frame[6]. NGS has revised its antenna calibration sheet to imitate the recent absolute antenna calibrations that are connected with IGS08, NAD 83(2011, MA11, PA11), specifically the IGS08 absolute antenna calibrations, though for consistent providing availability to previous reference frames the information of comparative antenna calibrations is also accessible. The absolute antenna calibrations might be different from equivalent comparative calibrations up to quite a few centimetres so professionals have to make sure they are applying the suitable information of calibration standards related with the specific reference frame that they are dealing in. To get the latest position coordinates that were presently explained the CORS team concluded a complete research of all information from CORS and from a set of worldwide stations with the objective of concurrently calculating a completely steady set of position coordinates, Earth Orientation Parameters (EOP) and GPS satellite orbits. This early Multi-Year CORS (MYCS1) attempt is the primary of a sequence of reprocessing developments that will take place regularly in the approaching years. The 7
previous time a research of CORS information happened was in 2002 and frequent glitches and variations have taken place in processing methods since that time. The concern above the overall performance of the explanations was not only restricted to NGS, but also to many other geodetic institutions, specifically IGS. Therefore IGS applied for membership in a reanalysis of all data information obtained since 1994 to set up a new reliable set of GPS satellite orbits, clocks corrections and EOPs. This plan was known as IG1/repro1. NGS designated to give to this attempt as an IGS Analysis Centre and utilized this chance to concurrently recycle all its CORS information to offer a single reliable set of position coordinates for all stations calculated by means of the finest accessible techniques[7]. 1.2
Research Background Since CORS sites locations change over the period of time with minimum an annual
and semi-annual dissimilarity, displacement rates cannot be strictly calculated until 2.5 years of GPS data or 130 weekly computations are analysed. Thus the assigned positions and velocities for stations with more than 2.5 years of GPS CORS data and 130 weekly estimations are calculated from NGS stacked method (MYCS1). For the other CORS stations, majority of presently installed stations, NGS calculate position and velocity. The velocity is modelled and calculated by means of the Horizontal Time Dependent Positioning (HTDP) software. The recent velocity model deals with only the 2-dimensional horizontal axes and a 0 (zero) velocity is adopted for the vertical axis. As the modelled displacement rates may not defines the real long-term movement of a CORS site and it may acquire some time to strongly approximate the displacement rates directly from the data, it is obviously recognized that the basis is either calculated or modelled. CORS site position coordinates are updated at regular intervals using the certain set of criteria. NGS observes the accuracy of its assigned position coordinates by means of each day solutions of the CORS system. After NGS obtains GPS CORS site data for a certain day, processing of the data is delayed by approximately 18hrs to get the IGS swift satellite orbits. NGS accumulates short-term time sequence plots of these explanations that show the dissimilarity of the CORS IGS08 position coordinates with respect to the assigned readings, corrected for the result of the adopted displacement rate. The each day remaining locations are in a regional geodetic topocentric frame, North, East, and Up (vertical). Theoretically, the plots specify how constantly every day result matches its' mean value, which, most probably indicates the result of perfect model effects. Thus contributing CORS team members, CORS operators and external users of CORS data regularly monitor these plots to
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make sure the performance of the CORS data they offer, share out and utilize. A sudden deviation in a CORS station's position often point to an antenna change, generally because of an antenna being replaced or deviated by any seismic activity or natural phenomenon (e.g. earthquakes, hurricanes). Though other apparatus replacements like GPS receiver improvement, firmware modification, or atmospheric variations e.g. new structure may also produce changes. Further steady movement may define an inaccuracy in the assigned displacement rate. This is usual for recent CORS stations which have modelled displacement rates particularly in the Up (vertical) component that is for all time assigned equal to zero, or atmospheric variations such as plants growth [8]. The extent of the perpendicular and horizontal errors are not essentially correlated, even though the daily disperse in latitude is characteristically less than the scatter in longitude, which in turn is usually smaller than the scatter in height. Big residuals are usually correlated with smaller than the time period of 24hrs of data, but may also define un modelled situations at the monitoring CORS sites for example high moisture, passing hurricane fronts, ionospheric error, neighbouring multipath, etc. The major inaccuracies are in the vertical axis and are steady with the complexity in modelling the environmental refraction (troposphere and ionosphere) and the physical obstruction of gathering GPS observation data files under the horizon[9]. The NGS did its last revision of position coordinates in 2012. Thus the CORS position coordinates are not updated due to seismic deviations associated with 23rd June 2014 Aleutian Islands earthquake and North American tectonic plate movements. 24hr Aleutian Islands earthquake observation data recorded by AB21 CORS site is used to precisely measure deviations of site associated with this seismic activity. This data is post processed with the help of RTKLIB software by using RTKPOST. The performance of AB21 CORS site to precisely measure an earthquake is analysed with respect to ADK IU Accelerometer measurements. For this purpose the Aleutian Islands earthquake data recorded by ADK IU Accelerometer is plotted for more accurate calculation of this seismic activity. To compute the deviation of this CORS site from its assigned position coordinates due to an earthquake, 60 days of post seismic post processed GPS data is used.
Also the deviations due to co seismic post seismic and inter seismic
activities are precisely measured to update positional coordinates of Adak AB21 CORS site in the region of Sitka Alaska. The revision of position coordinates also includes precise monitoring of North American Tectonic Plate movement[10]. The movement of North American tectonic plate movement is computed by means of GPS observation data recorded by AB21 CORS site. These observation data files are post processed by Online Position 9
User Service (OPUS) for precise positioning. The Last HTDP positional coordinates revision was done in 2013. The present version of HTDP software includes a post seismic motion model only for Denali earthquake of 7.9 magnitudes that hit Central Alaska on 3rd of November 2002. The recent HTDP 3.2.5 software version model does not include position coordinates variations associated with 23rd June 2014 Aleutian Islands earthquake. The AB21 CORS site observation data files are used to update HTDP computed position coordinates along x, y, z axes. These GPS observation files are post processed by OPUS to achieve centimetre level accuracy. 1.3
Research Motivations and Objectives The NGS CORS network and HTDP software are the key tools to achieve precise
position in both scientific research and industrial activity; however there is a need for determining accurate positions by eliminating atmospheric errors as well as errors induced due to seismic activities. Positioning performance can be quantified by the following metrics:
Accuracy
Precision
Initialisation time
Reliability
Availability
Continuity of positioning solution.
The CORS sites deviate from their assigned position coordinates with the passage of time. This deviation is caused by any seismic activity like an earthquake or volcanic eruption or it may be due to tectonic plate movement. Thus a rigorous computation is required to update any CORS site deviation from adopted coordinates.
NGS reviewed the published
(Official) NAD_83 position and velocities for a particular CORS site if one or more of the following situations occur, the antenna at CORS has been replaced, the position of CORS changed due to nearby earthquake or due to an error discovered during the computation of CORS position/velocity. NGS revised NAD 83 position coordinates for reference epoch 2010 in December 2012. HTDP is a service that incorporates major seismic activities that cause deviations of the reference points. This software permits users to convert positional coordinates across time and between different spatial reference frames. HTDP employs the equations of dislocation theory (Okada 1985) to measure co seismic motion for most of the 10
main earthquakes with magnitude greater than or equal to 6 that have happened in the USA and its regions since 1934. The present version of HTDP software includes a post seismic motion model only for Denali earthquake of 7.9 magnitudes that hit Central Alaska on 3rd of November 2002. The recent HTDP 3.2.5 software version model does not include position coordinates variations due to 23rd June 2014 Aleutian Islands earthquake. The novel contributions of this thesis are:
A performance analysis of AB21 CORS site and ADK IU accelerometer for the precise measurement of 23rd June 2014 Aleutian Islands earthquake.
The deviation of AB21 CORS site associated with Aleutian Islands earthquake is precisely measured by using 60 days post seismic data of the same site.
The North American Tectonic plate movement is precisely monitored by using CORS data.
The revision of AB21 CORS site position coordinates including all deviations associated with inter seismic, co seismic, post seismic activities and North American tectonic plate movement.
The revised AB21 CORS site position coordinates are used to update HTDP software measurements.
1.4
Statement of Need The NGS CORS sites deviate from their assigned position coordinates with the passage of time. These deviations are may be due to any seismic activity like an earthquake or volcanic eruption and tectonic plate movement. A rigorous computation is required to maintain position coordinates of NGS CORS network. CORS site position coordinates are updated at regular intervals using the certain set of criteria. NGS observes the accuracy of its assigned position coordinates by means of each day solutions of the CORS system. NGS obtains GPS CORS site data for a certain day, after processing of the data, NGS accumulates short-term time sequence plots of these explanations that show the dissimilarity of the certain CORS site position coordinates with respect to the assigned readings, corrected for the result of the adopted displacement rate. On 23 rd of 11
June 2014 an earthquake of magnitude 7.9 strongly hit the Aleutian Islands. This earthquake deviated Adak AB21 CORS site from its assigned NAD_83 (EPOCH 2010) position coordinates. NGS revised position of this CORS site last time in December 2012 by using 57 days of data. As the position coordinates of this CORS site are not revised after 2012, the present GPS data recorded shows a significant deviation of this CORS site from published position coordinates. This substantial deviation is due to Aleutian Islands earthquake and the North American tectonic plate movement. The North American tectonic plate is moving to the west-southwest at about 2.3 cm (approximately 1 inch) per year. A précised computation of all inter seismic, co seismic, post seismic activities and North American tectonic plate movement are required to revise Adak AB21 CORS position coordinates. The HTDP software is a service that permits users to convert positional coordinates across time and between different spatial reference frames. The Last earthquake dislocation model (3rd November 2002 Denali earthquake) incorporated into HTDP software was developed in 2013. This model was developed by Dr. Jeffery freymuller of the University of Alaska. The present version of HTDP software includes a post seismic motion model only for Denali earthquake of 7.9 magnitudes that hit Central Alaska on 3rd of November 2002. The most recent modification of Horizontal Time Dependent Positioning software version 3.2.5 has been done on August, 30 2015. It only modifies corrections for minor rounding error inconsistencies. The recent HTDP 3.2.5 software version model does not include position coordinates variations due to 23rd June 2014 Aleutian Islands earthquake. There is a need to develop Aleutian Islands earthquake dislocation model to update HTDP software position coordinates. This updating of Horizontal Time Dependent Positioning (HTDP) software measurements will include all crustal displacements due to seismic activities associated with 23rd June 2014 earthquake. 1.5
Rudiments of Research Methodology The initial phase involved the precise measurement of 23rd June 2104 Aleutian Islands earthquake. The AB21 CORS site recorded the Aleutian Islands earthquake data, a 24hrs GPS observation data that depicts all co seismic and post seismic movements associated with the earthquake. This GPS observation data file is in RINEX format and post processed with RTKLIB software by configuring RTKPOST. To achieve precise measurement of this earthquake, satellite navigation data file (n), precise satellite orbits (.sp3) file and for satellite clock corrections (.clk) files are used. Antenna Exchange
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format (ANTEX) .atx file is used for antenna calibrations that provides models to correct for the antenna phase carrier variations. The position (.pos) file is used to plot variations in position coordinates of AB21 CORS site during the earthquake along three dimensions. The earthquake data is also recorded by ADK IU accelerometer, and used to monitor earthquake amplitude variations during this seismic activity. The ADK IU accelerometer recorded acceleration of the site during this seismic activity and CESMD computer processed this data. The computer processed data of IU ADK accelerometer includes displacement and velocity along three dimensions 90 degree component, 360 degree component and up component. The IU ADK recorded data is given for a certain time period. In this time period the earthquake achieved its maximum peak. The 60 days of post seismic GPS data used to compute the deviation of AB21 CORS site associated with Aleutian Islands earthquake. The each day observation data file recorded by AB21 site is post processed by using Online Position User Service (OPUS) to achieve cm level accuracy. This data includes displacement of CORS site due to earthquake and also some post seismic movements. The deviation of the site due to North American tectonic plate movement is also computed since 2006 to till December 2016. The same CORS site data is used and post processed by OPUS to monitor North American tectonic plate movement. The precise measurement of 23rd June 2014 Aleutian Islands earthquake and North American tectonic plate movement are used to update the position coordinates. The Horizontal Time Dependent Positioning (HTDP) software measurements are taken throughout the year of 2014 and compared with the observations of AB21 CORS site to compute the difference between them. This comparison is used to calculate the dissimilarities between the measurements. All precisely computed deviations due to inter seismic, co seismic, post seismic activities associated with 23rd June 2014 earthquake and North American tectonic plate movement are used to revise Adak AB21 CORS site position coordinates. These revised position coordinates are used to update Horizontal Time Dependent Positioning (HTDP) software measurements. 1.6
Thesis Layout
Chapter 02 provides a brief introduction of The National Oceanic and Atmospheric Administration (NOAA) and National Geodetic Survey (NGS). This chapter deals with the history of the CORS network, its features, and strategies for its improvement in upcoming years. Engineers, Surveyors, scientists, GIS users, and the public that gather GPS data can
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utilize CORS data to get better accuracy of their positions. This chapter goes into the applications of CORS e.g. crustal motion, multipath studies, and atmospheric studies which includes ionospheric and tropospheric studies. It also includes the introduction and functioning of Online Position User Service (OPUS) and User Friendly CORS (UFCORS).
Chapter 03 describes the details of Horizontal Time Dependent Positioning (HTDP) software. This chapter contains the description of different utilities offered by the HTDP software like the estimation of horizontal crustal velocities and displacements, updating of position coordinates from one date to another and from one reference frame to another reference frame. This chapter has information about HTDP software velocity grids and rigid tectonic plate velocity models. The earthquake dislocation models incorporated into HTDP software are also described in this chapter.
Chapter 04 goes into development of different International Terrestrial Reference Frame (ITRF) realisations. This chapter briefly explains the development of International Terrestrial Reference System and different ITRF realisations. This chapter includes the introduction of NAD83 and WGS 84 realisations. It also includes the role of GPS in the evolution of different ITRF realisations.
Chapter 05 contains recorded GPS data and final results. In this chapter the Aleutian Islands earthquake data recorded by AB21 CORS site and ADK IU accelerometer is plotted to present earthquake variations. The post seismic data recorded by AB21 CORS site is used to measure the deviation of this CORS site from its assigned coordinates. This data is post processed by OPUS. The AB21 CORS site deviation due to North American tectonic plate movement is precisely estimated with the help of post processed GPS observation data. All these accurately measured deviations are used to revise AB21 CORS site position coordinates. These revised position coordinates are used to update Horizontal Time dependent Positioning (HTDP) software measurements.
Finally, Chapter 06 presents a review of the conclusions obtained from this research work and suggests some recommendations for advance research in this field.
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02 NATIONAL GEODETIC SURVEY (NGS) CORS NETWORK The National Oceanic and Atmospheric Administration‘s National Geodetic Survey (NGS) supervises the Continuously Operating Reference Station (CORS) system that consist of a network of approximately 2000 stations, each containing a geodetic value Global Navigation Satellite System receiver. NGS gathers, processes, and allocates data from these sites in holdup of precise exactness three-dimensional positioning actions all over the United States, its regions, and at a small number of overseas countries. CORS data are in addition used by meteorologists, geophysicists, weather and ionospheric scientists, and others in prop up of a broad selection of functions. This chapter deals with the history of the CORS network, its features, and strategies for its improvement in upcoming years. Engineers, Surveyors, scientists, GIS users, and the public that gather GPS data can utilize CORS data to get better accuracy of their positions. CORS augmented post-processed coordinates come close to a few centimetres compared to the National Spatial Reference System, both vertically and horizontally. The CORS network is a versatile supportive effort relating educational, government, and private associations[11]. The stations are separately possessed and functional. Every group contributes their data with NGS, and NGS examines and allocates the data free of cost. In August 2015, the CORS network almost 2,000 stations, contributed by more than 200 various associations, and the network keeps on expanding. 2.1
Introduction The CORS network is closely linked to the National Oceanic and Atmospheric
Administration (NOAA‘s) National Geodetic Survey (NGS) and this organization‘s task is to sustain, and offer access to the U.S. National Spatial Reference System (NSRS). The NSRS comprises the authorized system of the civilian government for facilitating a user to decide geodetic latitude, longitude, height and orthometric height, gravitational acceleration, and deflection of the vertical in the U.S.A and its terrains. The NSRS includes information about its course and range comparative to ITRF. NGS accepted the prospective assistance of the Global Positioning System (GPS) for developing the NSRS in the near the beginning phase of GPS advancement. NGS rapidly transformed its conventional horizontal field operations ―which applied line-of-sight instruments" to 3D field operations by means of GPS instrumentation. NGS first used GPS to 16
find out positional coordinates for the brass disks and previous monuments that served as conventional reference sites. NGS works together with different states and others to establish a high accuracy reference network (HARN). For every HARN survey, many new reference marks were positioned so that, as contrast to the previous reference marks, the new coordinates would be situated in more available places, e.g. close to the public road and rail network and/or they would offer a comparatively fewer hindered vision of the sky. These state wide HARNs were fixed into a more precise national network whose points were also positioned using GPS practices, first in 1987 and then in 1990. Once a HARN survey was finished in a certain state, NGS carried out a state-wide alteration of the HARN data, jointly with all recorded standard geodetic surveys and local GPS developments completed in that state, to calculate steady positional coordinates for the linked ground marks. To execute precise HARN surveys, NGS introduced, in the fall of 1986, the Cooperative International GPS Network (CIGNET), the precursor of the CORS network. All CIGNET sites were capable of a high quality dual frequency GPS receiver that constantly recorded signals from GPS satellites[12]. The main purpose was to make reliable tracking data accessible from a network of ground stations to calculate accurate ephemerides (Orbits) for the GPS satellites. In 1989, CIGNET contained three stations in America (MOJA in Mojave, Calif.; RICH in Richmond, Fla.; and WEST in Westford, Mass). These early CORS sites were capable of Mini-Mac 2816-AT dual-frequency codeless receivers Aero Service Division, Western Geophysical Company of America, Houston. In 1990, CIGNET extended into the southern regions. In 1991, CIGNET contained 21 sites covering all continents except Antarctica. All tracking data were gathered by numerous partners and accessible to GPS researchers through NGS records. Steadily, NGS improved the CIGNET network, producing the hub of the first public global GPS network that, unintentionally at the time, developed into the present International Global Navigation Satellite System (GNSS) Service IGS network in the sponsorship of the International Association of Geodesy. The concept of covering the whole USA with a CORS network to increase the NSRS was first suggested by Strange (1994). Soon after, Strange and Weston published an initial explanation of the CORS network. At the same time, numerous other federal organizations were also prepared to launch networks of continuously operating GPS base sites, but due to many reasons. The American Coast Guard (USCG) desired to increase its LORAN radio navigation service by offering the differential GPS (DGPS) service to sustain secure naval navigation in U.S coastal waters. In the same way, the U.S. Army Corps of Engineers (USACE) required a navigation system to prop up their inland waterway activities Dredging, hydro graphic surveys, etc. They work together 17
with the USCG to expand the DGPS facility inland along the main rivers. Finally, the Federal Aviation Administration (FAA) sought to use some type of CORS to maintain secure air navigation. The FAA built up their Wide Area Augmentation System (WAAS)[13]. Other federal organizations like NASA‘s Jet Propulsion Laboratory (JPL) and the U.S. Geological Survey previously greatly invested in using CORS sites to find out satellite orbits and to observe crustal motion. Since the late 1980s, the data from both CIGNET and JPL sites were utilized to support worldwide GPS orbit calculation. In 1994, NGS officially began constructing the CORS network by mounting a GPS receiver on the campus of the National Institutes of Standards and Technology, previously called the National Bureau of Standards, in Gaithersburg, Md. Six months later, NGS established a GPS receiver near Boulder, Colo. And with time integrated into the CORS network a number of continuously operating GPS fiducial sites that initially were element of CIGNET. Data from all these stations were made accessible using the Internet and, gradually, NGS included particular U.S. stable GPS base stations to the CORS network. The USCG and USACE began fixing their DGPS stations and FAA their WAAS sites in 1995. NGS worked with these organizations to integrate both the DGPS and WAAS sites into the CORS network. The preliminary stage of the USCG network was mainly done by January 1996. Other federal, state, and locally supported continuously operating receivers were recognized and steadily integrated into the CORS network from 1995 onwards. By 1995 NGS attained access to approximately 50 geodetic worthy GPS receivers, many installed by the USCG and other contributing organizations without the requirement by NGS to fix, sustain, or run any of the stations. The Texas Department of Transportation was the first state organization to connect the CORS system with the addition of their ten-station Regional Reference Point network that offered sufficient coverage in Texas. By 1996 the figure of CORS sites had enhanced to 85. By making contact with concerned organizations and planning to replace data, NGS extended the network to 108 stations by December 1997. The 200-site target was exceeded in 2000, and since then the CORS network has developed to its recent mass of approximately 2000 stations. At present, the CORS network contains stations in the United States, Canada, Mexico, Central and South America, the Caribbean, and Iraq. More than 200 associations contribute in the program [14].
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Figure 2.1 The NGS CORS site map Currently a few stations of Earth Scope‘s Plate Boundary Observatory (PBO), established in the west of the North American tectonic plate to observe crustal motions, have been integrated into the CORS network. Determining the orthometric height of a CORS site may need particular techniques, depending on the site and the sort of antenna fixing. The U.S CORS system has become the ideal technique for precise 3D positioning in America and out of the country. The benefit to GPS users is that they only require organizing a GPS receiver and downloading, matching CORS data using the Internet to process this data in a particular method. The Web-based utility, UFCORS has made these downloads simple. NGS is functioning with scientists to build up digital models and practices that will allow GPS users to find out precise positions efficiently and in an opportune method [15]. NGS has modernized its guidelines for launching CORS sites, enhanced its tracking of metadata, and advanced its GPS examination software known as PAGES.
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Figure 2.2 More than 280 CORS sites in Cascadia are part of the US plate boundary observatory (PBO). 2.2
CORS and Definition Of The NSRS NGS copied the original comprehension of the North American Datum of 1983 (NAD
83) in 1986 by applying a precise modification of standard geodetic explanations in its records jointly with Doppler readings and a a small number of very long baseline interferometry (VLBI) baselines. This original comprehension is called NAD 83 (1986). With progress in information of International terrestrial reference frame (ITRF), NGS has established numerous new realizations of NAD83, refining at every step the assigned coordinates. In 1998 NGS initiated the existing realization, called NAD 83 (CORS96), which is based on the CORS network by applying a transformation from ITRF96 to NAD 83. In both reference systems, ITRF and NAD 83 (CORS96), the three dimensional positional coordinates of every CORS is balanced by a three dimensional velocity to report for any crustal motion. In 2000 an ITRF realization is published known as the ITRF2000. ITRF2000 coordinates and velocities may be changed to NAD 83 (CORS96) readings using equations and constraints explained by Soler and Snay (2004). The NAD 83 (CORS96) positional coordinates are allocated for an epoch date of 2002.0, except in Alaska and California where epoch dates of 2003.0 and 2004.0, respectively, have been assigned due to earthquakes. It is necessary to apply the assigned velocities to calculate positional coordinates for any other reference date. It is necessary to note that CORS sites 20
situated in Hawaii and some Pacific islands have been used to describe the NAD 83 (PACP00) reference frame for the Pacific tectonic plate[16]. CORS sites situated in Guam are used to describe the NAD83 (MARP00) reference frame for Mariana tectonic plate. CORS sites are used to find precise geodetic control in some countries like Mexico and Jamaica. When a CORS comes on line, NGS utilized minimum ten 24-h GPS data sets to calculate its ITRF2000 positional coordinates comparative to other sites in the worldwide IGS network. NGS used the horizontal time-dependent positioning HTDP software to calculate the site‘s ITRF2000 velocity. Every few years, NGS reprocesses each CORS site data recorded since 1994 to calculate temporary positional coordinates and velocities for each CORS site comparative to the present ITRF comprehension: the difference between current and previous realization may be more than 1 centimetre in the east-west or north-south directions or by more than 2 centimetre in the upward direction, then NGS assigns the provisional positional coordinates and velocities to supersede the formerly assigned ITRF realization. For validation process, NGS executes a solution for each day to observe the value of assigned CORS positional coordinates. Each solution contains all CORS data recorded in the 24-hrs time spanning that day [7]. As a by-product, NGS collects plots showing differences between the assigned positional coordinates and the readings gained from the each day solutions, corrected for seismic motion, for the latest 60 days. The conclusions are plotted comparative to a local horizon (north-east-up) coordinate frame and are made obtainable to civilians via the CORS Web page (ftp://www.ngs.noaa.gov/cors/Plots/ xxxx.pdf) where xxxx denotes the site‘s four-character identification. The replacement or motion of the antenna due to unpredicted geophysical phenomenon may change the position of the CORS reference coordinates. Seismic activities (Earthquakes, volcanic activity, etc) may also create sufficient CORS site displacements that should be recorded. This information is essential to CORS user to find out precise positional coordinates. When the data of the 60-day series of every day estimates differ from this site‘s assigned positional coordinates if it is more than the ranges given in the previous paragraph (1 centimetre horizontal; 2 centimetre vertical) then NGS cautiously examines the accessible data to find out whether this site is deviated from its reference coordinates or not . Similar examination is completed with respect to the assigned NAD 83 (CORS96) position coordinates. When the daily provisional coordinates of the NAD 83 frame differ by more than 2 centimetres horizontally or by more than 4 centimetres in upward direction, then NGS assign new NAD 83 positional coordinates and velocities to all CORS sites. Due to these less rigorous tolerances, assigned NAD 83 (CORS96) positional coordinates and velocities are unlikely to be modernized as compared to ITRF realizations. 21
This NGS rule, applied in 1999 is being discussed at NGS for possible modification to lower tolerances in reaction to both external and internal requirements. For those organizations whose stations are integrated in the CORS network, NGS calculates very precise three dimensional positional coordinates and velocities in the NSRS for their stations antennas, offer a worldwide data sharing system, observe the status of the antennas on a every day basis, and informs the organizations when the change in the position of the antennas are noticed . In return, the organizations inform NGS when they replace hardware or software so that NGS can keep CORS data users up to date of the performance of the CORS sites. Scientists who observe very small motion of the Earth‘s crust are particularly concerned in any antenna replacements or movements so that they can describe for those effects when they take on long-term examination of CORS positional coordinates. When antenna movements are noticed and adjustments made, NGS instantly publishes this information through the CORS Newsletter. The On-line Positioning User Service (OPUS) utility was the first organized access to the NSRS via GPS. OPUS is an automatic facility that needs the user to provide only a small amount of information; its commands are self-descriptive and its Web page includes sufficient particulars to be followed simply http://www.ngs.noaa.gov/OPUS/. OPUS has a few limitations users should be aware of: first, OPUS offers a differential GPS static solution. Second, at least 2 hrs of GPS readings are suggested to get surveying-geodetic precision. Third, a maximum of 48 hrs of GPS data is allowed, the GPS data can cross midnight just one time. Fourth, the submitted data file should include dual-frequency! L1/L2" carrier phase observables. OPUS offers the geospatial community with positioning mentioned to both the ITRF2000 and the NAD 83 (CORS96) reference frames. OPUS regularly attains accuracies (accounted as ―peak-to-peak‖ values) better than 2 centimetre in the horizontal direction and 5 centimetre in the vertical direction by using data from three near CORS sites. The foundation of OPUS is the GPS data and the fiducial control obtainable from the CORS sites. The real concept of making CORS to support GPS surveying performances achieved a new level of competence with the development of OPUS. The geodetic, surveying, mapping, and GIS societies have adopted OPUS with immense eagerness. On January 31, 2007, the first variation of OPUS, called OPUS-RS (Rapid static), was affirmed ―initially‖ operational. Similar to the original implementation of OPUS, OPUS-RS calculates positions in differential method for dual-frequency data gathered by a GPS receiver. The uniqueness about OPUS-RS is a new processing engine, permitting as small as 15 min of data. The user can provide GPS data to OPUS-RS by accessing[17]. Another variation of OPUS is OPUS-DB (database) that 22
requires a minimum of 4 h data but provides users the option of recording the resultant positional coordinates in an NGS database for civil convenience. Finally, OPUS Mapper is developed to process L1 code data to find positional coordinates sufficiently precise for mapping and GIS applications. Each of these functionalities is developed in stages and a part of an integrated ―OPUS‖ utility. 2.3
Data Archives All CORS Site data are gathered at two services, one situated in Silver Spring, Md.
and the other in Boulder, Colo. At each service, the GPS data are prepared into a variety of kinds of designed files ―RINEX, Hatanaka, etc." for community sharing. People may freely use these data files and associated metadata via anonymous file transfer protocol [18]. In January 2000, NGS initiated a new interface to the CORS web site. This new interface is known as CORSAGE ―CORS Amiable Geographic Environment" because it facilitates people to use CORS data and metadata by using a sequence of geographic maps. The CORS homepage itself features an index map in which the whole region of CORS range has been separated into numerous color-coded areas, each generally concerning a few states. On a local map, a user can choose on the map sign indicating a certain CORS site to get a window including a regional map that locates this site‘s position corresponding to near inhabitant‘s centres, main roads, and other geographic characteristics. A list of options comes into view to the left of the regional map which allows users to download certain details about this site, for example a file having the site‘s positional coordinates and velocity. An additional thing on this list of options allows users to show a schedule displaying with 10 min resolution the time duration when CORS data are obtainable for this site. Examining such schedules can save users from downloading and processing files that have unwanted data breaks. Other list of options give availability of the site‘s navigation data and to files having significant evocative information about this site (category of GNSS kit, concerned organization, contact person, detail information of receiver and antenna substitutes, etc). 2.4
UFCORS and OPUS In November 1998, NGS launched the ―user-friendly‖ CORS ―UFCORS" data server
that facilitates users to request and obtain GPS data and related metadata ―satellite ephemeris and station-specific descriptive information" for sites in the CORS network by means of the World Wide Web [20]. UFCORS offers a suitable option to both the unidentified FTP information server and the Web-based ―standard‖ CORS data server for regaining CORS detailes. UFCORS permits a user to choose complete detail for a certain site and a certain 23
time period. Unspecified FTP and the standard CORS data server offer the detail only in the arrangement that is stored at NGS, while UFCORS can repackage the data into any of numerous arrangements for example by using UFCORS anyone can download GPS information files for any optional number of hours. In addition UFCORS permits users to choose GPS data files. UFCORS can interrupt GPS files to sampling rates, instead of standard 30-s rate. UFCORS can devastate recorded CORS information files of one sampling rate to a user suggested sampling rate of better value. Unidentified FTP remains the mainly accepted CORS data server in conditions of data quantity. Greater than 581GB of CORS information files were shared by means of unidentified FTP in April 2008, while UFCORS shared nearly 66 gigabytes in April 2008. Unidentified FTP is the server of selection among users that received GPS information files from various CORS sites on a periodic basis. Users who receive CORS data file occasionally or only from some sites like better to use UFCORS. The Online Positioning User Service (OPUS) offers easy availability to précised National Spatial Reference System (NSRS) position coordinates. Upload a GPS observation data file recorded with a high end survey GPS receiver and get an NSRS position by means of email. An OPUS need minimum user input and utilizes software which calculates position coordinates for NGS' Continuously Operating Reference Station (CORS) system. The post processed position coordinates are precise and reliable with other National Spatial Reference System users. calculated NSRS position coordinates are sent confidentially by email, and can also be shared openly using the NGS website.
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Figure 2.3 depicts the working of OPUS OPUS uses a static or rapid-static procedure, depending on the time period of GPS observation data file. Static files are post processed by PAGES static software. The position coordinates are averaged from three independent, single-baseline solutions, each base line calculated by double-differenced, carrier-phase measurements from one of three nearby CORS station. Rapid-static files are post processed with RSGPS rapid-static software[14]. Rapid-static post processing uses more affective algorithms to determine carrier phase ambiguities, but has an additional severe data stability and geometry needs; consequently there are a few distant areas of the country in which it will not be effective. 2.5
CORS Applications The area of CORS functions is diverse and versatile and it is usual that this tendency
will carry on in the future. CORS network has already made an effect on Earth sciences and also has significant impact on atmospheric studies. In the following parts, we explain some areas where the utilization of CORS data was remarkable in progressing scientific information. 2.6
Multipath Studies In case of GNSS antennas, multipath errors are due to the intrusion of signals that
have reached the GNSS receiver antenna by various paths, typically due to one path being rebound or reflected from the earth surfaces or buildings, fences etc The multipath effects 25
knowledge is significant to interpret the methodical errors related with a certain site and receiver antenna.
Figure.2.4 a CORS site antenna surrounded by buildings inside the city In 2004 Hilla and Cline performed an enquiry to assess the quantity of multipath happening at every of 390+ stations included in the National CORS network. This working categorized the most and least affected CORS sites in the network, evaluated various receiver/antenna arrangements, and examined intimately those stations that showed to be badly affected by multipath factor. Dual-frequency carrier phase and pseudo range readings were used to calculate the extent of L1 and L2 pseudo range multipath at each station over a one-year time period. A related study relating CORS and IGS sites also conclude that the postfit phase remaining parts were extremely reliant on the GNSS antenna type. This study concluded that the choke rings antenna types are extremely effectual in repressing multipath and that multipath is extremely dependent on the certain surroundings at each CORS site. 2.7
Crustal Motion Crustal movement observation is maybe one of the main obvious of all CORS
purposes. If CORS information files are thoroughly processed and examined in a time of some years, then the movement of the Earth‘s crust can be observed where the CORS network gives adequate coverage. ―Gan and Prescott 2001" examined GPS data found between the years 1996 and 2000 for 62 CORS sites spread all over the central and eastern American States. Their conclusions propose that no observable horizontal crustal movement happened during this time interval in this region of the state, except in the lower regions of Mississippi River Valley. This certain region appears to be accelerating towards southward comparative to the remaining parts of the continent at an average rate of 1.7 mm/year. This 26
speed is not statistically important; the reality that the movement happens close to New Madrid, Mo .where earthquake hazard is considered to be high argues that the movement perhaps real. Sella et al. 2002 applied GPS data from the CORS sites, jointly with information files from a worldwide division of CORS sites, to generate a worldwide ―recent velocity‖ ―REVEL" model that measures the movements of nineteen tectonic plates and continental slabs during the 1993–2000 time period. Park et al. (2002) got data from sixty CORS sites to calculate the higher and inferior mantle thickness by evaluating radial station displacement rates with velocities contingent from glacial isostatic adjustment (GIA) models. Also their GPS calculated displacement rates are steady with preceding calculations gathered using various techniques and data files for different time periods. ―Dokka et al. 2006" used GPS data from CORS sites to infer that southeast Louisiana, including New Orleans and the big Mississippi Delta, are both collapsing vertically and approaching southward with respect to the inner layer of the North American tectonic plate.
Figure 2.5 depicts the deviations of NGS CORS sites due to seismic activities 2.8
Sea Level Changes The changes of upward crustal displacement rates at CORS sites close to tide gauge
stations may be used to approximate the ―absolute‖ sea level variation relative to the International Terrestrial Reference Frame. This kind of investigation was not possible to carry out before the propagation of CORS in oceanographic lands. A study by Snay et al. 2007 connecting 37 tide gauge sites, spread along the U.S. and Canadian shore areas, such 27
that each is situated within 40 km of a CORS site, examined strictly the crustal velocity close to tide gauge sites from GPS readings spanning between three and eleven years. After adjusting past tidal data with these estimated crustal velocities, the conclusions explain that the average rate of absolute sea level varies equals 1.8mm/year for the 1900–1999 time period. The same study estimated the absolute rate of sea level variation equals −1.19 mm/year along the southern Alaskan shoreline. This decreasing of absolute sea level close to southern Alaska is most likely due to continuous melting of glaciers and ice masses. With time, more CORS data files will become accessible close to tide gauges to perform examinations able to precisely calculate vertical crustal velocities and absolute sea level rates with better certainty. 2.9
Tropospheric Studies The interruption of GPS signals, which is due to the refractivity of the troposphere or
electrically neutral atmosphere, is related with, pressure, temperature and the division of water vapor at height of nearly 16 km. If the atmospheric pressure is estimated with reliable precision at the height of the GPS receiver antenna, then the total ―wet‖ and ―dry‖ delay at the CORS can be efficiently divided with small error. Mapping the resultant wet signal delay into the included ―total column" precipitable water vapour ―IPW" is accomplished in a simple way if the average vapour-weighted temperature of the troposphere is accurately known. Water vapour is the most significant ingredient of the atmosphere. It is the cause of clouds and rainfall, and an element in main weather actions. IPW changes very much over the planet: approximately 0.5 cm close to the poles and 5 cm close to the equator. Approximately 95% of the water in the atmosphere exists under 5 km or in effect below the 500 hPa pressure surface". Sufficient variations in the vertical and horizontal division of water vapour can happen quickly minutes to hours in case of dynamic climate. NOAA‘s Earth Systems Research Laboratory (ESRL) previously called NOAA‘s Forecast Systems Laboratory, has evolved the ability to approximate the spatial and sequential change of tropospheric delay in the nearby United States CONUS. Their forecast procedure is supported on modelling the delay using GPS readings from the CORS network in arrangement with other meteorological information. They modernize their model every one hour. It is probable to use CORS network to calculate the tropospheric signal delay at every site with better precision due to rigorous instrument needs for good precision GPS positioning. Information from 385 CORS sites included hourly into the functioning version of
28
the rapid update cycle (RUC) arithmetical weather forecast model which consigns the conclusions to a two-dimensional ―2D" horizontal grid having a 13-km nodal gap. The Global Systems Division of NOAA‘s ESRL started NOAATrop, a recent method to get better GPS precision and timing accuracy using live weather data at CORS network. This data offers zenith wet delay and ALT ―a proxy for zenith hydrostatic delay" for a two dimensional grid with 13-km power resolution over the CONUS. NOAATrop is dependent on RUC, a functioning model that is modernized hourly basis. The rms precision of the modelled delays is at present 20 mm in winters and 40 mm in summer. 2.10
Ionospheric Studies Wide region ionospheric models have been evolved to model and alleviate local
ionospheric errors. Such models are based on dual frequency readings from a subset of the GPS CORS sites. The ionosphere is a dispersal medium situated in the area of the higher atmosphere that starts at an elevation of nearly 50 km and extends in upward direction few hundred kilometres. The electromagnetic rays from the Sun and particles entering from the magnetosphere produces free electrons and ions that is the reason of phase advances and group interruptions in radio waves. The condition of the ionosphere is a function of the strength of solar and magnetic activity, location on the Earth surface, local time and other issues. As GPS signals cross the ionosphere, they are attenuated by a quantity directly proportional to the total electron content (TEC) in the ionosphere at a known time. On a daily basis maps representing the evaluation of TEC over the CONUS depended on CORS data files from approximately 180 CORS sites have been formed at NGS and shared via Internet since 1997. NOAA‘s Space Weather Prediction Centre (SWPC) initiated modelling total electron content in three dimensions for CONUS using CORS sites information files. This model is modernized each 15 min of time period with a discontinuation of thirty min. This product is planned to enumerate total electron content over CONUS to real time and has developed through teamwork between the ESRL, NGS, SWPC, and NOAA‘s National Geophysical Data Centre. Data files from the CORS sites have been used in understanding of large-scale ionospheric attenuations due to geomagnetic storms on a continental level. Analysis to verify for ionospheric errors in regional CORS network for example Ohio State developed for real-time kinematics ―RTK" purposes have propagated with the operation of state functioned CORS networks. GPS data files from CORS network have been used to verify ionospheric models designed to get better longer baseline differential GPS positioning of rovers using only L1 carrier phase data. Finally it is initiated to calculate complete 29
―unambiguous" Total Electron Content (TEC) readings depending only on dual frequency ambiguous carrier phase data from the CORS sites, while the effort was only an investigation model. 2.11
Geo Location of Aerial Moving Platforms GPS Data accessible from CORS network also used in various remote sensing
applications. The precise positioning of air vehicles working in aerial mapping is essential to get better consistency of photogrammetric restitution mainly for larger-scale aerial analysis applications over distant or unreachable topography. The similar ideas applied for geo locating landmarks from the height with digital cameras has been extended to a wide arrangement of mapping territory features with cutting edge technologies like light detection and ranging ―LiDAR", scanning radar interferometric synthetic aperture radar, and/or sonar , inertial systems. The use of CORS GPS data files in aerial mapping procedures has established to offer an essential option. The service of CORS network in DGPS air vehicle positioning was studied by ―Booth and Lunde 2003" representing that precise carrier phase differential values can be acquired by means of much longer baselines than initially suggested. The air born mapping society benefit from the increasing number of CORS network. Possibly, the important issue in all these applications is the availability to GPS data files at a 1-s sampling rate as a substitute of the standard of 30-s sampling rate. NGS has assisted with federal, state, and confidential organizations to plan in front of time variations at certain CORS sites to the 1-s sampling rate. This assists the post processing of aerial GPS data files to precisely calculate the positioning coordinates of a plethora of air born moving platforms e.g., NGS‘s Remote Sensing Division gains air born imagery to measure tornado damage. These tasks are well done by CORS sites data files, gathered at a 1-s sampling rate, to precisely conclude the journey path of the air vehicle being used to get air born imagery. NGS workers worked intimately with their CORS associates to provisionally augment data sampling rates after the storms of 2005. The imagery of regions affected by an entity storms is obtainable at NGS website. 2.12
The Future of NGS CORS Network In December 2006, NGS established a new CORS site close to the tide gauge station
situated in Key West, Fla. This CORS site will assist transmit local ocean height variation at Key West to the internationally reliable, strictly defined International Terrestrial Reference Frame. NGS planned to establish a CORS site at each of numerous extra tide gauge sites controlled in the U.S. National Water Level Observation Network ―NWLON". Installed in 30
1913, the Key West tide gauge site is one of the best continually operational stations controlled in the NWLON. The new CORS site at Key West is also important as it is the first CORS, established by NGS, which receives both American GPS and Russian GLONASS data. A figure of CORS associates have started improvement of CORS sites to receives both GPS and GLONASS data files, and NGS also begin distributing such GNSS data to CORS users. In addition, many CORS sites are streaming GNSS data in real time to NGS head office in Silver Spring, Md. NGS will transmit these data files to the public in real time to prop up the expansion of local GNSS networks that allow real-time positioning in the United States. In reaction to user requirements, more than forty associations, both public and private, are now installing such local GNSS CORS networks. Also, many more of these local real time positioning systems are predicted to be installed in the near future. NGS requires to maintain these systems by establishing suitable principles and procedure so that: broadcasted positional coordinates and velocities for the related GNSS base stations are attuned with the NSRS, User tools can function with facilities from various real time GNSS systems to the maximum level achievable, and Sites controlled in every real-time system meet approved criteria in terms of constancy and data excellence. NGS supports the organizations, who are offering real-time positioning utilities, to use the NGS given data files in their processes so as to add the data from other GNSS sites, and use the position and velocities of the GNSS sites controlled in the NGS real-time network as fiducial readings for calculating position and velocities of other real-time GNSS CORS sites. NGS is streaming these data files as people should have real-time access to data files from Government supported sites in the CORS network. It is significant to highlight that NGS aims to stream only the GNSS observables and not ―correctors‖ to these observables. NGS does not propose to stream GNSS data files that are already being streamed by other association. In all probability, NGS use NTRIP ―networked transport of RTCM standard via internet protocol" to transmit the stream of GNSS observables via Internet .
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03 3.1
HORIZONTAL TIME DEPENDENT POSITIONING (HTDP) SOFTWARE Introduction HTDP is a service that permits users to convert positional coordinates across time and
between different spatial reference frames. HTDP is abbreviation of ―Horizontal TimeDependent Positioning‖. It facilitates users to execute each of following six purposes:
Estimate horizontal crustal velocities
Estimate crustal displacements from one date to another
Update (or backdate) positional coordinates from one date to another
Transform positional coordinates from one reference frame to another and/or from one date to another
Transform certain types of geodetic observations from one reference frame to another and/or from one date to another
Transform crustal velocities from one reference frame to another.
HTDP offers the given services in most of the latest comprehensions of the North American Datum of 1983 (NAD 83), also in all authorized comprehensions of the International Terrestrial Reference System (ITRS) and all official realizations of the World Geodetic Reference System of 1984 (WGS 84) . Users may operate the most recent version of HTDP software interactively on the worldwide-web at http://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.shtml. This file has Fortran-90 source code for HTDP software. A user will require to accumulate and connect this source code to produce executable code to operate on his computer. The web site also contains the most recent version of the HTDP User‘s Guide, having instructional practices model data files for operation with the instructional practices. 3.2
Estimating Horizontal Crustal Velocities HTDP measures crustal movement in terms of
Steady inter seismic horizontal velocities
Co seismic motion, i.e. sudden variations in positional coordinates, that happens within a few minutes of an earthquake.
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Post seismic motion, i.e. the transient movement following an earthquake which depending on the earthquake‘s magnitude may remain geodetically assessable from as small as a small number of days to as extended as some decades.
Some Other types such as periodic motion also occur, but the recent revision of HTDP does not accommodate these other types of seismic motion. To calculate steady inter seismic displacement rates, HTDP slots in seventeen areas, each area has two types. With the first type, HTDP uses a two dimensional rectangular grid (in latitude and longitude) across an area for which displacement rates at the grid nodes have been earlier measured from geophysical and geodetic Information. In this type of area, HTDP employs bilinear interpolation to calculate the two dimensional velocity at a user-identified position by using the quantified two dimensional velocities for the grid nodes, particularly, the four grid nodes at the corners of the two dimensional grid cell having this position. Table 1 list the ten regions of this type, and provide pertinent information about these regions [19]. Table.3.1 Represents a velocity grids used in HTDP software Region
Latitude Range
Longitude Range
Node Spacing (minutes)
San Andreas
35.8°N – 36.79N
120.51°W – 121.8°W
0.6
114°W - 121°W
3.75
119°W - 125°W
3.75
122°W - 125°W 107°W - 125°W 66°W - 107°W 140°W - 148°W
3.75 15.0 30.0 15.0
143.25° - 162°W
15.0
130°W - 142°W 130°W - 170°W
15.0 15.0
Southern 31°N - 36°N California Northern 36°N - 40°N California Pacific Northwest 40°N - 49°N Western CONUS 31°N - 49°N Eastern CONUS 24°N - 50°N St. Elias, Alaska 56.5°N - 63°N South-Central 53.25°N – Alaska 65.75°N Southeast Alaska 54°N - 63°N Mainland Alaska 56°N - 73°N
Reference
Pearson and Snay (2013) for horizontal velocities; vertical velocities have been set equal to 0.0 mm/yr Relative to ITRF2008. Snay et al. (2013) for horizontal velocities; vertical velocities have been set equal to 0.0 mm/yr Relative to ITRF2008.
In case of second type area, HTDP utilizes rigid tectonic plate models to calculate horizontal velocities by using given equations
Vx Tx Ry z Rz y
(0.1) 34
Vy Ty Rz x Rx z
(0.2)
Vz Tz Rx y Ry x
(0.3)
Here (x, y, z) indicate Earth-cantered, Earth-fixed Cartesian (ECEF) Cartesian coordinates for a user- specified position; ( Vx , V y , Vz ) represent the three dimensional displacement rates at this position; ( R x , R y , R z ) represent the angular velocities (rotation rates) about the Cartesian coordinates; and Tx , Ty , Tz indicate the linear velocities (translation rates) along x-axis, y-axis, and z-axis. When the position coordinates are represented in meters and the rotation rates in radians/year, then the calculated velocities will be represented in meters/year. In this type of region vertical velocities equal to zero for specified positions. Table 2 gives the seven areas of this type and offers some relevant data about these regions. Table. 3.2 Plate motion rates encoded into HTDP (positive rotation rates are counter clockwise). Tectonic Ṫx Ṫy Ṫz Ṙx Ṙy Ṙz Frame Reference Plate mm/yr mm/yr mm/yr nrad/yr nrad/yr nrad/yr North Altamimi et al. ITRF2008 0.41 0.22 0.41 0.170 -3.209 -0.485 America (2012) Altamimi et al. Caribbean ITRF2008 0.41 0.22 0.41 0.238 -5.275 3.219 (2012) Altamimi et al. Pacific ITRF2008 0.41 0.22 0.41 -1.993 5.023 -10.501 (2012) DeMets et al. Juan de Fuca ITRF2008 0.41 0.22 0.41 6.626 11.708 -10.615 (2010)* DeMets et al. Cocos ITRF2008 0.41 0.22 0.41 -10.390 -14.954 9.148 (2010)* Mariana ITRF2000 0.00 0.00 0.00 -0.097 0.509 -1.682 Snay (2003) DeMets et al Philippine ITRF2008 0.41 0.22 0.41 -0.841 3.989 -10.626 (2010)* Sea * DeMets et al. (2010) offers the rotational velocities of this plate with respect to the Pacific tectonic plate[20]. For each of the three rotation rates (calculated by DeMets et al.), its readings has been included to the related ITRF2008 rotation rate of the Pacific tectonic plate (as approximated by Altamimi et al.(2012)) to get the related ITRF2008 rotation rate for the tectonic plate[20]. When someone identifies a position, HTDP will step through the 17 regions in a particular manner until this service finds the first area that includes the particular position. It will then 35
utilize the model for this area to calculate the three dimensional displacement rate at this position. If the particular position is not present in any of the 17 regions, then HTDP outputs a message to the consequence that it is not able to calculate the velocity for this position. While using HTDP software to calculate displacement rates at a set of positions, a user may interactively give positional coordinates for the positions one at a time or a person may enter an ASCII file that gives coordinates for all of the positions in the set. HTDP allows two different file arrangements, each of which is explained during the implementation of the HTDP software facility. A user can identify a two dimensional grid (Lat, Long) and enquire HTDP to calculate displacement rates at the nodes of this grid. Also, a user may identify a line (that is a geodesic on an ellipsoidal shaped Earth) and request HTDP to calculate displacement rates at evenly spaced positions along this line (geodesic). A user must state the reference frame in which he is giving the positional coordinates to HTDP software. The HTDP-calculated rates will then also be mentioned to this reference frame. 3.3
Estimating Crustal Displacements HTDP may be utilized to calculate the crustal displacement at an identified position
from time t1 to time t2 . The calculated displacement equals the velocity at this position multiplied by the difference of time intervals t2 t1 added to all post seismic and co seismic motion that has happened between these two time intervals. The user has selection to enable HTDP calculate three dimensional velocities to be utilized in this process, or he may interactively provide the displacement rate to be used. HTDP employs the equations of dislocation theory (Okada 1985) to measure co seismic motion for most of the main earthquakes with magnitude greater than or equal to 6 that have happened in the USA and its regions since 1934 [21]. Table 3 lists the earthquakes whose dislocation models are encoded into the current version of HTDP.
Table 3.3
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Date m-d-yr
06-07-1934 05-17-1940 10-21-1942 07-21-1952 03-19-1954 06-26-1966 04-09-1968 02-09-1971 03-15-1979 08-06-1979 10-15-1979 05-02-1983 04-24-1984 08-04-1985 07-08-1986 07-21-1986 10-01-1987 11-24-1987 10-17-1989 04-22-1992 04-25-1992 06-29-1992 01-17-1994 10-16-1999 12-22-2003 10-28-2004
Earthquake dislocation models incorporated into HTDP Earthquake Source of Model (magnitude)
Parkfield (M=6.0) El Centro (M=6.9) San Jacinto (M=6.6) Kern County (M=7.5) San Jacinto (M=6.4) Parkfield (M=5.6) Borrego Mtn. (M=6.5) San Fernando (M=6.6) Homestead Valley (M=5.6) Coyote Lake (M=5.9) Imperial Valley (M=6.4) Coalinga (M=6.4) Morgan Hill (M=6.2) Kettleman Hill (M=6.1) N. Palm Springs (M=5.6) Chalfant Valley (M=6.2) Whittier Narrow (M=5.9) Superstition Hill (M=6.6,6.2) Loma Prieta (M=7.1) Joshua Tree (M=6.1) Cape Mendocino (M=7.1) Landers/Big Bear(M=7.5,6.6) Northridge (M=6.7) Hector Mine (M=7.1) San Simeon (M=6.5) Parkfield (M=6.0)
CALIFORNIA Segall and Du, 1993 Snay and Herbrectsmeier, 1994 Snay and Herbrectsmeier, 1994 Snay and Herbrectsmeier, 1994 Snay and Herbrectsmeier, 1994 Segall and Du, 1993 Snay and Herbrectsmeier, 1994 Snay and Herbrectsmeier, 1994 Stein and Lisowski, 1983 Snay and Herbrectsmeier, 1994 Snay and Herbrectsmeier,1994 Stein and Ekstrom, 1992 Snay and Herbrectsmeier, 1994 Ekstrom et al., 1992 Savage et al., 1993 Savage and Gross, 1995 Lin and Stein, 1989 Larsen et al., 1992 Lisowski et al., 1990 Bennett et al., 1995 Oppenheimer et al., 1993 Hudnut et al., 1994 Hudnut et al., 1996 Peltzer, Crampe, & Rosen, 2001 Johanson, 2006 Johanson et al., 2006 ALASKA
03-28-1964
Prince William Sound (M=9.2)
Holdahl and Sauber, 1994
11-03-2002
Denali (M=7.9)
Elliott et al., 2007 MEXICO
04-04-2010
El Mayor – Cucapah (M=7.2)
HTDP implements the following equation
37
Fialko, personalcommunication,2010
t ti Di , j , , Ai , j , 1 exp Qi
(0.4)
Di , j , , t 0
(0.5)
To model the progressive post seismic motion Di,j(φ,λ,t) from initial time t i to final time t, which is related with earthquake i and dimension j (j = north, east, or up) and which happened at the position with longitude λ and latitude φ . Here Ai,j(φ,λ) represents the amplitude (in meters) related with earthquake i and dimension j at the position with longitude λ and latitude φ , t i represents the time of happening of earthquake i, and Q represents the relaxation constant related with earthquake i. The present version of HTDP includes a post seismic motion model for only the M7.9 Denali earthquake that happened in central Alaska on November 3, 2002. This model was developed by Dr. Jeffery Freymueller of the University of Alaska, Fairbanks. This model offers amplitudes Ai,j(φ,λ) at the nodes of a two dimensional rectangular grid(LAT, LONG). HTDP utilizes bilinear interpolation to approximate relevant amplitudes at other geographic positions within the grid‘s width. For other earthquakes, their post seismic motion has been deserted or included into relevant models for co seismic motion. While using HTDP to calculate displacements at a set of positions, a user may co-actively offer positional coordinates for the positions one at a time or he may enter an ASCII file that gives positional coordinates for all of the positions in the compilation. HTDP allows two file formats, each of which is explained during the implementation of the HTDP service. Also, a person can identify a two dimensional grid (LAT, LONG) and request HTDP to calculate displacements at all of the two dimensional grid nodes. Also, a person may identify a line and enquires HTDP to calculate displacements at evenly gaped positions along this geodesic line. A HTDP user should identify the reference frame in which he is offering the positional coordinates to HTDP. The calculated displacements will also be mentioned to this reference frame[22]. 3.4
Updating Positional Coordinates When using HTDP software, positional coordinates for a position are supposed to
change with the passage of time. Thus when identifying positional coordinates, it is also essential to identify the time to which they mention. This time is known as reference epoch or reference date. 38
When updating (or backdating) positional coordinates with HTDP, a person must identify:
The reference frame,
The starting positional coordinates and their reference epoch t1 , and
The reference epoch t2 for the updated coordinates.
Then HTDP calculates the displacement vector for time interval ∆t this vector to the initial positional coordinates to get the position at time t2 . When revising a set of positional coordinates, the coordinates may be submitted interactively one at a time or the positional coordinates may be submitted all together in an ASCII file. HTDP allows two unlike file formats, each of which is explained during the implementation of the HTDP service. 3.5
Transforming Positional Coordinates While transforming positional coordinates from one reference frame to another, a
person must identify:
The initial reference frame and the initial positional coordinates,
The reference epoch t1 of the initial coordinates,
The reference frame for the transformed coordinates, and
The reference epoch t2 of the transformed coordinates.
This positional coordinates transformation is a two-step process:
Update the positional coordinates from initial time to end time in the starting
reference frame.
Transform the updated positional coordinates at time t2 from the initial reference
frame to the required reference frame. Let x(t)A ,y(t)A, and z(t)A indicate the positional coordinates of a position at time t referred to reference frame A in a three dimensional Earth-cantered, Earth-Fixed (ECEF) Cartesian coordinate system. These positional coordinates are represented as a function of time to reflect the reality of earth crustal movement. In the same way, let x(t)B, y(t)B, and z(t)B represent the positional coordinates of this same position at time t referred to reference frame B also in a three dimensional
ECEF Cartesian coordinate system. Within HTDP
software, the positional coordinates in frame A are approximately connected to those in frame B through the following given equations of a 14-parameter transformation: 39
x t B Tx t 1 s t ·x t A Rz t ·y t A – Ry t ·z t A
(0.6)
y t B Ty t – Rz t ·x t A 1 s t ·y t A Rx t ·z t A
(0.7)
z t B Tz t Ry t ·x t A – Rx t ·y t A 1 s t ·z t A .
(0.8)
In
these equations
Tx(t),
Ty(t) and Tz(t) are
translations
along
the x-, y-
and z-
axis, respectively; Rx(t), Ry(t) and Rz(t) are counter clockwise rotations about these same three axes; and s(t) is the differential scale between reference frame A and reference frame B. These estimated equations are sufficient because the three rotations along Cartesian coordinates have comparatively little magnitudes. It is important that all the seven quantities are characterized as a function of time as modern geodetic technology has allowed scientists to notice their time-related changes with some precision. In HTDP software, these timerelated changes are supposed to be linear, so that all seven quantities may be represented by an equation of the form:
P t P P· t –
(0.9)
Where τ represents a specific time of reference and the quantities, P(τ) and Ṗ, are constants. Thus, all the seven quantities provide rise to 14 parameters, but it is important to note that the values of seven of these parameters depend on the value selected for τ. For descriptive reasons, suppose a transformation from NAD 83(CORS96) coordinates to ITRF96 coordinates. A point‘s velocity in NAD 83(CORS96) is represented as if the ―stable‖ core of the North American tectonic plate does not shift on average. On the other hand, its ITRF96 velocity is represented as if the main tectonic plates displace according to the no-netrotation NUVEL-1A model of DeMets et al. (1994). According to this model, ―the North American plate is rotating counter clockwise at a constant rate about an axis that passes through both the Earth‘s centre of mass (i.e., the geocenter) and a point on the Earth‘s surface slightly west of Ecuador‖ [23]. The ITRF96 reference frame has rotation comparative to the
40
NAD 83(CORS96) frame and vice versa. This relative movement may be measured by identifying suitable standards for the three rotation rates Ṙx, Ṙy and Ṙz. The remaining four rates are not necessary to measure this movement. While changing coordinates from ITRF96 to NAD 83(CORS96), the present version of HTDP software utilizes the equations accepted by the U.S. National Geodetic Survey and Canada‘s Geodetic Survey Division:
Tx t 0.9910 0.0 t 1997.00
(0.10)
Ty t 1.9072 0.0 t 1997.00
(0.11)
Tz t 0.5129 0.0 t 1997.00
(0.12)
Rx t 125.033 0.258 t 1997.00 10 9
(0.13)
Ry t 46.785 3.599 t 1997.00 10 9
(0.14)
Rz t 56.529 0.153 t 1997.00 10 9
(0.15)
S t 0.0 0.0 t 1997.00
(0.16)
In the following given equations, τ = 1997.00 which corresponds to January 1, 1997.Currently, HTDP requires to compatible with more than a dozen ITRF realizations. Rather than store the 14 parameters for every probable combination of two reference frames, HTDP software utilizes two mathematical estimations to decrease its storage requirement. Specifically, as all rotation angles are comparatively small, all the 14 parameters for the transformation from Frame A to Frame C nearly equal to the addition of its equivalent parameter from Frame A to Frame B and its equivalent parameter from Frame B to Frame C (if all three conversions utilize the similar τ value). This association may be expressed by the representative equation
A C A B B C
(0.17)
Where A C indicates the conversion from Frame A to Frame C. It is also the condition that
A B B A
(0.18)
41
That is, all the 14 parameters for the transformation from Frame B to Frame A equals its equivalent parameter for the conversion from Frame A to Frame B multiplied by -1.0. As a result of above two equations, HTDP software hoards only the 14-parameter essential for converting from ITRF94 reference frame to each other reference frame. Therefore, for converting coordinates from reference Frame A to reference Frame B, HTDP uses the symbolic connection
A B ITRF A ITRF B 3.6
(0.19)
Transforming Observations When changing an observation, such as a calculated distance between two positions,
the user has to identify:
The type of observation
The observed value
The date on which the examination was calculated
The positional coordinates of the related positions,
The reference frame and the reference epoch of the given coordinates, and
The date to which the transformed observation is to correspond.
To alter a collection of observations, the user must give the first four types of information (observation type, observed value, observation date, and the positional coordinates of the related positions) using a BlueBook file (Federal Geodetic Control Subcommittee 2000). HTDP software will then produce a new BlueBook file in which the observational accounts from the input BlueBook file have been restored with equivalent accounts that hold modernized values for the observed quantities. These positional coordinates must all be referred to the same reference frame (indicated F0 ) and the similar reference epoch (indicated t0 ), both of which the user will be enquired to provide during the implementation of HTDP software. HTDP software can modernize different types of observational records included in a BlueBook file, containing those for distances, azimuths, horizontal dimensions, horizontal angles, and three dimensional interstation vectors (imitative from GPS data). The BlueBook file should include positional coordinates for each site related with the observations to be altered. The user may or may not require to identify the initial and final reference frames, 42
since a number of observations (like chord distances) are constant in comparison with the reference-frame option while other observations (such as three dimensional interstation vectors imitative from GPS data files composed concurrently at pairs of positions) do depend on positional coordinates reference-frame option[24]. Let C t1 symbolize an observed chord distance between two positions A and B at time t1 . To approximate the equivalent distance C t2 that would have been calculated at time t2 , the HTDP software will initially repossess positional coordinates for A and B from the positional accounts of the BlueBook file. These positional coordinates are mentioned to reference frame F0 at time t0 . HTDP software will modernize them to equivalent positional coordinates for A and B in reference frame F0 at time t1 and then use these modernized positional coordinates to calculate the untested distance C t1 between points A and B at given time t1 Likewise, HTDP software will modernize the initial positional coordinates for points A and B to equivalent positional coordinates in reference frame F0 at time t2 and calculate the untested distance C t2 at time t2 . The untested distance C*(t1) can be different from the observed distance C t1 for numerous causes. First, C t1 includes some quantity of observational errors that is not measured in measuring C t1 . Second, the positional coordinates for point A and B given in the BlueBook file might be different from the real positional coordinates of points A and B at time t0. And third, any imprecision in the encoded crustal movement models will influence the value of C t1 . For these similar causes, C t2 will be different from C t2 , but the dissimilarity C t2 C t2 must estimated the dissimilarity C t1 C t1 in value since both dissimilarities engage basically the similar errors. As a result, the expression: C t1 C
t2 C t1
Calculates C t2 . Therefore, HTDP software places C t2 for the assessment of this formula. The service modernizes other types of observations, that are reference-frame constant, in a same way.
43
Now let Dx t1 F1 ,
Dy t1 F1 , Dz t1 F1 indicate a three dimensional difference vector
between positions A and B at given time t1 as mentioned to reference frame F1 . To change this vector to its related vector at time t2 and alluded to reference frame F2 , HTDP software will utilize a three-step process:
Convert the initial three dimensional difference vector from reference frame F1 to reference frame F0 at time t1 .
Modernize the resultant vector from time t1 to time t2 in reference frame F0 , and
Convert the resultant vector from reference frame F0 to reference frame F2 at time t2 .
For the very first step, HTDP software employs the equations: Dx t1 F0 i s t1 Dx t1 F1 Rz t1 Dy t1 F1 Ry t1 Dz t1 F1
(0.20)
Dy t1 F0 Rz t1 Dx t1 F1 1 s t1 Dy t1 F1 Rx t1 Dz t1 F1
(0.21)
Dz t1 F0 Ry t1 Dx t1 F1 Rx t1 Dy t1 F1 1 s t1 Dz t1 F1
(0.22)
Here Rx t1 , Ry t1 , and Rz t1 are the three rotations from reference frame F1 to reference frame F0 at time t1 and s t1 is the differential scale change from reference frame F1 to reference frame F0 at time t1 . In second step, HTDP software recovers the positional coordinates for positions A and B from the Blue Book file. HTDP software then modernizes these positional coordinates in reference frame F0 from time t0 to relevant positional coordinates at time t1 and also to relevant positional coordinates at time t2 . HTDP software then employs the given equation: Dx t2 F0 Dx t1 F0 Dx t1 F0 X B t2 x A t2 x B t1 x A t1
(0.23)
To calculate the x-component of the three dimensional difference vector at time t2 as mentioned to F0 . Here xi(tj) mentions to the x-component of the three dimensional earth
44
centred earth fixed ECEF Cartesian positional coordinates of position i at time t j as mentioned to F0 [25]. 3.7
Transforming Velocity Vectors While transforming a velocity vector at position C from reference frame A to
reference frame B, the users have to identify:
The velocity vector in reference frame A, and
The positional coordinates of position C in reference frame A.
HTDP software then converts the input velocity Vx A , Vy A , Vz A in reference frame A to equivalent velocities in reference frame B using the given equations:
Vx B Vx A Tx s x Rz y Ry z
(0.24)
V B V A T
(0.25)
y
y
y
Rz x s y Rx z
Vz B Vz A Tz Rx y s z
(0.26)
Here (x, y, z) indicates the three dimensional earth centred earth fixed ECEF Cartesian positional coordinates of position C mentioned to reference frame A; ( Tx , Ty , Tz ) indicates the three translation rates of reference frame B comparative to reference frame A; Rx , Ry Rz indicates the three rotation rates of reference frame B comparative to reference frame A; and ṡ indicates the rate of differential scale change of reference frame B comparative to reference frame A. While using HTDP software to change a set of velocity vectors from one reference frame to other reference frame, the person may interactively give the necessary data one position at a time or he may enter an ASCII file that includes the necessary data for all positions. The format of this ASCII file is explained during the implementation of the HTDP software service.
45
Figure.3.1 The velocity model of North American tectonic plate.
Figure 3.2 represents the velocity model of East and West CONUS 3.8
Reference Frames Recognized By HTDP When a user enters positional coordinates into HTDP software, he will require to give
the reference epoch (or date) to which these positional coordinates correspond. If the user is not sure as to the right reference epoch, then he may submit either (1) the date on which the observations utilized for calculating the positional coordinates were carried out or (2) the default reference epoch related with the reference frame to which the coordinates are mentioned. The key in the below table is the number that the HTDP software employs to classify a specific reference frame. It is important to note that some reference frame realisations have 46
the same key number. This key number is only significant to persons who build up HTDP software and its applications that will directly appeal to the HTDP software. The given table has information about the reference frame realisation incorporated with Horizontal Time Dependent Positioning (HTDP) software, different domains with their by default reference epoch with important links and information. The Horizontal Time Dependent Positioning (HTDP) software computed values are dependent on reference frame realisations as each grid node has different position Coordinates in each reference realisation.
Table.3.4 Reference frame realisations accepted by HTDP software
47
Reference Frame
Domain
Default Reference epoch
Responsible Agency
Key
NAD 83(2011)
CONUS,Alaska, Puerto Rico, U.S. Virgin Is.
2010
NGS
1
NAD 83(PA11)
U.S. islands on Pacific plate
2010
NGS
2
NAD 83(MA11)
U.S. islands on Mariana plate
2010
NGS
3
NAD 83(NSRS2007) or NAD 83(2007)
CONUS,Alaska, Puerto Rico, U.S. Virgin Islands
2007.00 in California, Oregon, Washington, Nevada, and Arizona;2002.00 otherwise
NGS
`1
Pursell and Potterfield, 2008
NAD 83(CORS96)
CONUS,Alaska, Puerto Rico, U.S. Virgin Is.
2003.00 in Alaska,2002.00 otherwise
NGS
1
Soler and Snay, 2004
NAD 83(PACP00)
U.S. islands on the Pacific plate
1993.62
NGS
2
Snay, 2003a
NAD 83(MARP00)
U.S. islands on the Mariana plate
1993.62
NGS
3
Snay, 2003a
Global
Date of observation
DoD
5
True, 2004
Global
1994
DoD
6
True, 2004
Global
1997
DoD
7
True, 2004
Global
2001
DoD
8
True, 2004
Global
2005
DoD
9
Global
2005
DoD
10
Global
1988
WGS 84(TRANSIT) WGS 84(G730) WGS 84(G873) WGS 84(G1150) WGS 84(G1674) WGS 84(G1762) PNEOS 90 & NEOS 90 SIO/MIT 92 ITRF88 ITRF89 ITRF90 ITRF91 ITRF92 ITRF93 ITRF94 ITRF96
Global Global Global Global Global Global Global Global Global
1992.57 1988 1988 1988 1988 1994 1995 48 1996 1997
More Information
www.geodesy.noaa.gov /CORS/coords.shtml
14 IERS IERS IERS IERS IERS IERS IERS IERS
11 12 13 14 15 16 17 18 19
IERS Ann. Rep. for 1988 IERS Tech. Note No. 6 IERS Tech. Note No. 9 IERS Tech. Note No. 12 IERS Tech. Note No. 15 IERS Tech. Note No. 18 IERS Tech. Note No. 20 IERS Tech. Note No. 24
ITRF97 ITRF2000 ITRF2005 ITRF2008 IGS97 IGS00 or IGb00 IGS05 IGS08 or IGb08
3.9
Global Global Global Global Global
1997 1997 2000 2005 1997
IERS IERS IERS IERS IGS
20 21 22 23 20
IERS Tech. Note No. 27 IERS Tech. Note No. 31 Altamimi et al., 2007 Altamimi et al., 2011 Kouba, 2009
Global
1998
IGS
21
Kouba, 2009
Global
2000
IGS
22
Kouba, 2009
Global
2005
IGS
23
Rebischung et al., 2011
Software Characteristics Users can execute the most recent version of HTDP software interactively on the
World Wide Web at http://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.shtml. A user will need gathering and connecting this HTDP software source code to generate executable code that is well-matched with the operating system on his computer. This source code is in FORTRAN90 format. The horizontal time dependent positioning software is menu-driven and mainly data is submitted interactively. Users may also submit particular data in batch files if users desire to practice data for multiple positions, e.g. to convert positional coordinates for various positions across time and/or between different reference frames. HTDP software admits batch files in three different formats. One is known as ―BlueBook" format for horizontal control data e.g. if asked for, the software will calculate approximately displacements and displacement rates for all positions containing an 80 record in an active BlueBook file. The second format for batch ingress engages a data file with numerous files where (for changing positional coordinates) every file has the format: LAT, LON, EHT, TEXT Here, LAT = latitude in degrees (positive north) LON = longitude in degrees (positive west) EHT = ellipsoid height in meters TEXT = descriptive text (maximum of 24 characters) The individual fields in each record may be separated by commas or blanks. The format is slightly different for estimating displacements between two dates, and again the format is slightly different for transforming velocities between reference frames. 49
The third format for batch entry engages a file with several records where (for changing positional coordinates) each record has the format: X, Y, Z, TEXT Here, X, Y, and Z are Earth-centered, Earth-fixed (ECEF) Cartesian positional coordinates represented in meters and TEXT = descriptive text (maximum of 24 characters.
50
04 4.1
Research on Geodetic Datum
Introduction Surveyors, GIS/GNSS professional and others who work in North America face
challenge of dealing with three different three dimensional terrestrial reference systems. For numerous authorized activities, these professionals present positional coordinates in North American Datum of 1983 (NAD 83) reference frame. On the other hand, sometimes they support using the World Geodetic System of 1984 (WGS 84) for a variety of on field coordinates positioning work connecting the Global Positioning System (GPS), or often they find the International Terrestrial Reference System (ITRS) more appropriate for attaining better positional correctness. As these three reference systems are different from one another conceptually they differ slightly, but they have significant difference in case of there realisation, as the realization of a specific reference system is known as ―reference frame‖. A specific reference frame is typically recognized by assigning positions and displacement rates for numerous accessible points. Currently there are many realizations of each of these three reference systems, as research institutions have scientifically updated positions and velocities with the passage of time to maintain speed with how developing technology has enhanced positioning precision. Now, we examine the development of these reference frames, and also explain conversion of positions between different reference frames. At last, we deal with some experimental considerations for précised positioning and describe strategies for a new North American datum 1983 (NAD 83) realization [26]. 4.2
Explaining a Reference System The current way to describing a three dimensional terrestrial reference system may be
separated into four parts. The first step associates the coordinate axes of a three dimensional Cartesian coordinate system to an arrangement of actually assessable positions on earth surface or within the earth. As a consequence, the position and direction of the three Cartesian coordinate axes are expressed. The second step associates the idea of distance to actually quantifiable quantities whereby a unit of length is described. The third step indicates an auxiliary geometric surface that approximates the dimension and shape of the earth. Finally, the fourth step indicates about the question of how Earth‘s gravity field adds to the concept of position, and particularly that of height. We are mainly concerned with only the first three steps, therefore focusing on the geometric features concerned in describing a reference system[27].
51
For the first step, majority of scientists worried in describing recent reference systems have the same opinion that the source of the three dimensional Cartesian coordinate system must be positioned at Earth‘s centre of mass (geocenter); also that the Cartesian coordinate system‘s z-axis must pass through the standard definition of the North Pole, or more accurately, the International Reference Pole (IRP) as described by the International Earth Rotation Service (IERS), a global association recognized in 1988 and its headquarter is in Paris, France. The x-axis has to go through the point of zero longitude situated on the plane of the standard equator, which is also described by the IERS. The meridian passing through this point is situated very near to the meridian of Greenwich while the two are not concurrent. The y coordinate axis makes a right-handed coordinate frame with the x-axis and z-axis. Indeed, all these three positional coordinate reference systems NAD 83, WGS 84, and ITRS have been described in concept. They have differences, though, in case of their realizations; that is, in how the position and direction of their relevant Cartesian axes have been actually expressed and also their relevant impressions of distance. Unfortunately, what at first appears to be a simple geometric procedure is complicated by Earth‘s dynamic behaviour. E.g. Earth‘s centre of mass has relative motion with Earth‘s surface. Earth‘s rotation and motions of Earth‘s rotation axis both have variations with respect to space (precession and notation) and to Earth‘s surface (polar motion). Also, coordinates points on the earth‘s crust are in motion with respect to each other due to seismic activities like tectonics plat movement, earthquakes, volcanic/magmatic eruption, ocean loading, postglacial recover, solid Earth tides, people‘s extraction of underground fluids and numerous other geo-physical phenomena. Current terrestrial reference systems, therefore, require to compatible for these motions. One option is to relate the Cartesian coordinate axes to the positions of certain points calculated at certain Instant of time (epoch). This option is usually utilized when concerning with the movement of the earth‘s rotational axis and with the movement related tectonic plate. Some other types of motion (for instance, subsidence) are considered for by adjusting the Cartesian coordinate axes to some temporal standard of the positions for particular points[28]. As there is a basic dissimilarity among the numerous reference frames engages how they encounter the motion related with tectonic plates.
In second step, scientists worried with describing advanced terrestrial reference systems have the same opinion that the unit of length, the meter or ―metre‖, is defined as ―the length of path travelled by light in a vacuum during a time interval of exactly 1/299,792,458 seconds‖. This explains the difficulty of describing the idea of distance to a actually quantifiable 52
quantity in theory, but not in realization. All the different reference frames connected with NAD 83, WGS 84, and ITRS relies on a separate set of readings that were executed using one or more of numerous extensively diverse types of tools and methods, among the most representative: Satellite laser ranging (SLR), GPS, electro-optical distance measuring instrumentation, very long base-line interferometry (VLBI) and Doppler satellite positioning. As every measurement type had been adjusted to agree with the definition of a meter, the measurements, however, include errors. As a result, the ―scale‖ of any specific reference frame is not precise. Particularly, when old traditional terrestrial reference frames are evaluated with recent ―space-age‖ reference frames, scale uncertainties at the part-per-million (ppm) level may often be detected. Due to current technical advancements in the calculation of time and, as a result, distance, scale dissimilarities between modern frames is now close to the part-per-billion (ppb) level [29]. In third step, the earth‘s surface is calculated in dimensions and shape with the geometric surface that is produced by rotating an ellipse about its smaller axis. The created surface is known as ―ellipsoid of revolution‖ or just ellipsoid.
Figure.4.1 shows the earth geodetic ellipsoid parameters The ellipsoid‘s geo-metric centre must be situated at the origin of the three dimensional Cartesian system, and its coordinate axis of radial symmetry (semi-minor axis) must intersect with the Cartesian z-axis of the certain terrestrial reference frame. The dimension and shape of the rotated ellipse is totally described by means of two parameters: the length of its semi53
major axis usually denoted a, ―which calculates the distance from the geocenter to a point on the equator (approximately 6,378 km). The length of the semi-minor axis, Denoted by b, ―this calculates the distance from the geocenter to the North Pole‖. Here the value of a is about 0.3% greater than b. The reason that b is shorter than a is a result of the force applied by Earth‘s rotation causing our earth to bulge in outward direction around its equator. Instead of using b, scientists often use the ellipsoid‘s flattening, f
a b
(0.27)
a
Different reference systems accept different ellipsoids. NAD 83 reference system and the Geodetic Reference System of 1980 utilize the similar ellipsoid as which was accepted by the International Association of Geodesy[30]. WGS 84 reference system utilizes an ellipsoid accepted by the National Imagery and Mapping Agency (NIMA, for-merely the Defence Mapping Agency), and international terrestrial reference system (ITRS) utilizes an ellipsoid accepted by the IERS. Corresponding values of semi-major axis a and flattening f are given in the table below. For the given readings of a and b (or f), a person can change three dimensional Cartesian positional coordinates x, y, z into the geodetic positional coordinates latitude, longitude, and ellipsoidal height and vice versa. These geodetic positional coordinates exemplify a particular instinctive method in identifying positions on and close to the earth‘s surface, as these coordinates connect to our native understanding of the horizontal and vertical directions[31].
Table.4.1 A comparison between different realisations
4.3
Reference System
Semi-major axis (m)
Flattening
NAD 83
6,378,137.0
1/298.257222101
WGS 84
6,378,137.0
1/298.257223563
ITRS
6,378,136.49
1/298.25645
The Evolution of NAD 83 In 1986 a group of organizations representative of many North American countries
introduced the first realization of North American Datum (NAD 83) to improve the earlier reference system (the North American Datum of 1927 or NAD 27). Particularly, the National
54
Geodetic Survey (NGS) of the United States formally refers to the very first NAD 83 realization as NAD 83 (1986). In this reference system realization, the group of organization depended a lot on Doppler satellite observations gathered at hundreds of sites to approximate the position of the Earth‘s centre of mass and the direction of the three dimensional Cartesian coordinate axes. They also depended on these similar Doppler observations to give range for NAD 83 (1986). The group of organizations relied on three dimensional locations derived by Doppler that had been transformed by: • A scale change of -0.6 ppm • A translation of 4.5 m along the z-axis • A clockwise rotation of 0.814 arc seconds about the z-axis
Positions derived by Doppler were so changed to build them steadier with the satellite laser ranging (SLR), very long baseline interferometry (VLBI) and terrestrial azimuth readings that were accessible in the early 1980s. As NAD 83 (1986) is three dimensional in scope, NGS accepted only horizontal positional coordinates (latitude and longitude) for more than 99% of about 250,000 United States control points that were concerned for the description of this coordinate reference frame. Unluckily, this first realization of NAD 83 happened a few years before GPS technology, which made the vertical measurement economically reachable [32]. 4.4
GPS Revolution At the same time that national geodetic survey accepted NAD 83 (1986), the
organization had started using GPS technology, rather than triangulation or trilateration, for horizontal axis positioning. The reality that GPS technology also offered précised ellipsoidal heights was fairly ignored in the 1980s it is because surveyors and other professionals of vertical axis locations needed orthometric heights in comparison to average sea level, which is attained with Spirit levelling, tide gauges and there was no requirement of geometric heights in comparison of an theoretical
supposed surface (the ellipsoid), as attained with
GPS technology. The approach in case of using GPS technology to calculate geodetic heights step by step developed, however, as national geodetic survey and some other organization established modernized geoidal models for measuring the height difference between average sea level and the ellipsoid. These developments allowed persons to change
55
ellipsoidal heights into orthometric heights with more precision. Furthermore, users can calculate heights much more efficiently with GPS technology as compared to spirit levelling [33]. As GPS technology established, the other geodetic technologies; particularly, SLR and VLBI also developed within a few years after 1986. GPS and SLR calculations had permitted geodesists to find Earth‘s centre of mass with an accuracy of a few centimetres. Both GPS and SLR technologies exposed that the centre of mass of earth that was assumed for NAD 83 (1986) is deviated by approximately 2 meter from the real geo-centre. Also, GPS, SLR, and VLBI discovered that the direction of the NAD 83 (1986) Cartesian coordinate axes is also deviated by more than 0.03 arc seconds in comparison with their real directions, and that the north American datum 1983 (NAD 83) scale varies by approximately 0.0871 ppm from the standard definition of a meter. These inconsistencies are due to major concern because the practice of most précised GPS calculations reproduced. Particularly, preliminary with Tennessee in 1989, every state in teamwork with national geodetic survey and many other organizations utilized GPS technology to develop local reference frame systems that were to be steady with NAD 83 reference frame[34]. The equivalent coordinate networks of GPS technology control points were initially called High Precision Geodetic Networks (HPGN). At present, they are known as High Accuracy Reference Networks (HARN). The recent name indicates the reason that comparative accuracies between HARN control points are more accurate than 1 ppm, while comparative accuracies between already existing control points were almost only 10 ppm. For description of these local reference frames, national geodetic survey reserved the position of the geocenter and the direction of the three dimensional Cartesian coordinate axes which already had been defined in 1986 from the converted Doppler measurements. This organization, though, selected to develop a new scale that would be compatible with the scale of the ITRS realization which is known as the International Terrestrial Reference Frame of 1989 (ITRF89). As the ITRF89 scale was depended on a set of GPS, SLR, VLBI and lunar-laser-ranging (LLR) readings. The final scale difference, equal to -0.0871 ppm, changed active NAD 83 latitudes and longitudes trivially, but it methodically reduced all ellipsoidal heights by approximately 0.6 m. Yet, this variation to a more précised scale serves the inclination toward using satellite based navigation technology for obtaining précised heights. So this second realization is also known as NAD 83 (HPGN) or NAD 83 (HARN); but this thing is important note that, this realization is basically a combination of local realizations that were developed more than a time period of many years (1989-1997) with every latest local realization being ―adjusted‖ so it become compatible with those 56
realizations that headed it.
4.5
NAD 83 3rd Realisation Included CORS In 1994, national geodetic survey developed a third realization of NAD 83 when the
organization prepared a network of continuously operating reference stations (CORS). Each CORS site contains a GPS receiver whose data files, national geodetic survey gathers, processes, and distributes for community use. Surveyors and GPS professionals can enter CORS data files to position points at which other GPS data files have been gathered with precision that is close to a few centimetres, both along horizontal and vertical axes. The CORS system initiated with nearly a dozen sites in December 1994, and it has established at a rate of about three CORS sites per month[35]. Figure indicates the current standing of the National CORS network.. The first computation of CORS sites positional coordinates is carried out in the ITRS realization known as ITRF93. NAD 83 coordinates were then calculated by using a Helmert transformation; these transformation equations are given below x
NAD83 TX 1 S X ITRF RZ Y ITRF R Y Z ITRF
(0.28)
y
NAD83 TY R Z X ITRF 1 S Y ITRF R X Z ITRF
(0.29)
z
NAD83 TZ RY X ITRF RX Y ITRF 1 S Z ITRF
(0.30)
Here TX , TY , and TZ indicate three translation along the x-axis, y-axis, and z-axis Cartesian coordinate axes, which will carry the origin of the two coordinate reference frames into intersection. R X , RY , and RZ express three rotations about the x-axis, y-axis, and z-axis, Cartesian coordinate axes respectively. It will carry the three coordinate axes of a single reference frame in to equivalent adjustment with their relevant coordinate axes in the other coordinate reference frame. At last, s indicates the variation in scale between the two coordinate reference frames. The values of these translations and rotations had been calculated so that the ITRF93 positional coordinates of nine VLBI sites in the USA would transform with more precision to their assigned NAD 83 (HARN) positional coordinates. The scale variation, s, was put equal to zero. These VLBI sites were utilized due to their more précised positions up to cm-level in both NAD 83 (HARN) and ITRF93. Now we use the label NAD 83 (CORS93) to recognize the reference frame achieved by doing this transformation to change CORS coordinate positions from ITFR93 to NAD 83. In early 1996, national geodetic survey calculated positional coordinates for all already established CORS sites so another ITRS realization, known as ITRF94 formulated. 57
Also, the organization formulated a Helmert transformation from ITRF94 to NAD 83 by means of eight of the similar VLBI sites (a VLBI site in California was not used for this purpose due to its seismic motion issue). In this case the scale variation again set equal to zero. National geodetic survey applied this latest transformation to change ITRF94 positional coordinates for the CORS sites to a fourth NAD 83 realization which is known as NAD 83 (CORS94).In the fall of 1998, national geodetic survey calculated positional coordinates for all already established CORS sites in the ITRS realization called as ITRF96 [36]. National geodetic survey worked together with Canada‘s Geodetic Survey Division to develop a Helmert transformation based on eight VLBI sites in the USA and four VLBI sites in Canadian territory. In this case the scale difference again adjusted equal to zero. Other assigned parameters for this transformation are expressed below. National geodetic survey applied the final transformation to change ITRF96 positional coordinates for the CORS sites to a fifth NAD 83 realization which is known as NAD 83 (CORS96). However national geodetic survey carries on to use NAD 83 (CORS94) positioning coordinates for all CORS sites, except those whose NAD 83 (CORS96) positioning coordinates deviated by more than 2 cm horizontally or 4 cm vertically from their assigned positional coordinates of NAD 83 (CORS94). There are five realizations of NAD 83 in the United States. A same development happened in Canada, but both countries agree on their initial and final realizations. The five realizations of United States are reliable in their selection of source and direction; they are different in their selection of scale. As the scale variation between NAD 83 (1986) and NAD 83 (HARN) is equal to -0.0871 ppm, the scale variation between NAD 83 (HARN) and any NAD 83 (CORSxx) realization is less than 0.005 ppm in magnitude. It must be noted that the NAD 83 (HARN) geodetic coordinates of a given control point may be different by more than one meter from its assigned NAD 83 (1986) positioning coordinate. Luckily, the horizontal inconsistency between the NAD 83 (CORS93) and NAD 83 (HARN) realizations locations for a control point is approximately for all time less than 10 cm, and the horizontal inconsistency between any two NAD 83 (CORSxx) coordinate positions for a control point is approximately every time less than 2 cm. Also, as NAD 83 has developed from mainly a horizontal reference system to a complete three dimensional reference system, the figure of control points with calculated ellipsoidal heights has developed dramatically [37]. The Department of Defence (DoD) established the WGS 84 reference system to prop up global activities relating mapping, charting, positioning, and navigation. Particularly, department of defence initiated WGS 84 to represent satellite orbits; that is, satellite positions as a function of time. Therefore, WGS 84 is generally used for ―absolute‖ 58
positioning activities so people suppose that satellite orbits are adequately precise to offer as the only source of control for positioning points of concern. Particularly, accurate positioning does not depend on using positional coordinates for already present terrestrial points for control, except not directly in that satellite orbits are obtained from assigned positions for a small collection of tracking stations. A common user, however, certainly not requires knowing the locations of these tracking stations. Department of defence offers both ―predicted‖ and ―post fit‖ satellite orbits in the WGS 84 reference system. As implicit by the name, predicted orbits are estimated in front of time by applying physical principles to conclude recently approximated satellite locations. On the other hand, post fit satellite orbits are estimated from earlier noticed satellite locations. Post fit satellite orbits are better in accuracy as compare to predict orbits as they are not depended to predicting the future and also they are generally obtained by means of a larger figure of tracking stations. GPS satellite predicted orbits and satellite clock parameters are produced by the USA Air Force at the GPS Operational Control Segment, situated at Schriever AFB, Colorado. The Air Force then transfers these predicted values to the GPS satellites so that this data might be included in the radio signal broadcasted by these GPS satellites. These predicted satellite orbits help all real-time precise positioning and navigation services relating GPS. Post fit GPS orbits and satellite clock parameters are produced by the National Imagery and Mapping Agency (NIMA), who currently creates this data obtainable on its internet sites [30]. Many other associations also produce post fit GPS satellite orbits which they commonly present in a certain International Terrestrial Reference System (ITRS) realization. The real WGS 84 realization basically is in agreement with NAD 83 (1986). Following WGS 84 realizations, however, approximate certain ITRS realizations. As GPS satellites transmit the predicted WGS 84 satellite orbits, persons who utilize this transmit data for positioning points attain positional coordinates that are compatible with WGS 84. Therefore, the fame of utilizing GNSS for real-time positioning has encouraged better utilization of WGS 84. In spite of its fame, persons usually do not utilize WGS 84 for better precision positioning tasks; as such tasks need the use of most précised positions on already present geodetic points for control. E.g. many differential GPS methods use estimated positions for one or more than one already present geodetic points to eliminate particular systematic uncertainties in calculating most accurate positions for new points. As a result, earlier than WGS 84 can assist better accuracy in positioning tasks, a quite widespread network of précised positioned WGS 84 terrestrial control points would have to be developed.
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Department of defence developed the real WGS 84 reference frame in 1987 by means of Doppler measurements from the Navy Navigation Satellite System (NNSS) or TRANSIT. The WGS 84 reference frames have developed considerably since the mid-1980s. In 1994, Department of defence launched a reference frame realization of WGS 84 that is depended totally on GNSS measurements, not on Doppler observations. This new reference frame realization is officially called as WGS 84 (G730) where the letter G represents ―GPS‖ and ―730‖ indicates the GPS week number (Starting at 0h UTC, 2 January 1994) when national imagery and mapping agency (NIMA) began representing their obtained GPS satellite orbits in this reference frame. The recent WGS 84 realization, known as WGS 84 (G873), is also depended totally on GPS measurements. Here also the letter G indicates GPS, and ―873‖ presents to the GPS week number initiating at 0h UTC, 29 September 1996. While national imagery and mapping agency began calculating GNSS or-bits in this reference frame on this date, the GPS Operational Control Segment did not accept WGS 84 (G873) until 29 January 1997. The foundation, direction, and scale of WGS 84 (G873) are estimated comparative to assigned positional coordinates for fifteen GPS tracking stations: 05 of them are sustained by the United State Air Force and other 10 stations are maintained by NIMA (see Fig.). National imagery and mapping agency select their stations to balance the equatorial sharing of the United States Air Force stations and to rearrange different sites view from each GPS satellite. Persons may expect further advancements of WGS 84 reference system in upcoming years, because latest GPS tracking stations may be added or already present GPS antennas may be transferred or repositioned. National imagery and mapping agency is devoted to obtain suitable observations to assure the best potential level of excellence and to continue the precision of WGS 84 reference frame. As stated previously, most of the areas be deficient in a network of available reference points that might offer as control points from which most précised WGS 84 positioning coordinates may be propagated by means of a suitable static differential GPS method relating carrier phase observables. Another minor disadvantage disturbing précised GPS activity is the absence to the GPS user of the crustal movements at the WGS 84 tracking sites. Further data about WGS 84 may be acquired by means of the Internet accessing: http:// 164.214.2.59/GandG/tr8350_2.html.
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Figure 4.2 Combined GPS Monitoring Stations 4.6
The Development of ITRS In the late 1980s, the International Earth Rotation Service (IERS) introduced
International Terrestrial Reference System (ITRS) to help those research tasks that need most précised positional coordinates; for, e.g. observing crustal movement and the motion of Earth‘s rotational axis. The first ITRS realization known as the International Terrestrial Reference Frame of 1988 (ITRF88). So international earth rotation service expressed locations and displacement rates for a global system of several hundred sites. The international earth rotation service, with the assistance of numerous helping organizations, obtained these locations and displacement rates by a variety of most accurate geodetic methods containing GPS, LLR, SLR, VLBI and DORIS (Doppler orbitography and radio positioning integrated by satellite). Each year after the introduction of ITRF88, the IERS has developed a new ITRS reference system realization as follows ITRF89, ITRF90... ITRF97 they published updated positional coordinates and displacement rates for already present stations, and also new positioning coordinates and displacement rates for those stations that had been developed since after very first reference frame realizations had been established [38]. Every latest realization is integrated with a current year of data, and also the latest comprehension of Earth‘s dynamic behaviour. The ITRF96 frame is defined by the locations and displacement rates of more than five hundred sites spread between nearly three hundred worldwide distributed stations. A specific station may engage one or more co-positioned tools utilizing many space related methods (e.g., GPS, VLBI, SLR, LLR, and DORIS). The precision and strictness of ITRS has confirmed compatibility, and its reputation is 61
progressively increasing between those who work in positioning tasks. ITRS is the first main international reference system to directly deal with tectonic plate and other types of crustal movements by revising displacement rates and positioning coordinates for its control points. To realize the requirement for velocities, suppose the concept of plate tectonics. According to this theory, Earth‘s outer surface consists of nearly 20 tectonic plates that are fundamentally rigid, and the movement of these plates are relative to one another like several large sheets of ice on a body of water. The comparative movements between points on different tectonic plates are, in some cases, are more than 15 cm/yr, which is easily measurable by using GPS and other current day positioning technologies. According to this fact that tectonic plates are moving with respect to each other, user may enquire how crustal displacement rates may be presented in ―absolute‖ conditions. The persons accountable for international terrestrial Reference frame recently deal with this problem by supposing that the Earth‘s crust, as a complete, does not displace ―on average‖ comparative to Earth‘s centre. Supposed in a different way, the worldwide developers suppose that the whole angular momentum of Earth‘s outer surface is zero. Therefore, the angular momentum related with the movement of any tectonic plate is neutralized by the collective angular momentum related with the movements of the other tectonic plates [39]. As a result, coordinate points on the North American tectonic plate usually deviate horizontally at quantifiable rates according to the international terrestrial reference system definition of absolute motion. Particularly, horizontal ITRF96 displacement rates have magnitudes between 1 and 2 cm/yr in the coterminous 48 states of America. Furthermore, horizontal ITRF96 displacement rates have even greater deviation magnitudes in Alaska and Hawaii.
Figure 4.3 Sites defining ITRF96
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On the other hand, the NAD 83 coordinate reference system deals with tectonic plate movement under the supposition that the North American plate, as a whole, does not deviate ―on average‖ comparative to Earth‘s interior. Therefore, coordinate points on the North American tectonic plate usually have no horizontal deviation comparative to NAD 83 reference frame unless they are situated close to the plate‘s border (California, Oregon, Washington, and Alaska) or they are deviated by some other seismic deformational process like volcanic/magmatic eruption activity, postglacial rebound, etc. The NAD 83 coordinate reference system, although, does make particular adjustments for specific American areas that are situated entirely on another tectonic plate. In Hawaii region, for e.g. NAD 83 positional coordinates are described as if the Pacific tectonic plate is not deviating. This concept is suitable for persons who are engaged with navigation tasks only in Hawaii. This concept, although, indicates a sheet of difficulty for users who are engaged in coordinate positioning points in Hawaii comparative to coordinate points in North America. In the case of earth crustal motion, it is unsuitable to identify positional coordinates without identifying the ―epoch date‖ for these positional coordinates; that is, the reference date to which these positional coordinates related [40]. So, ITRF96 coordinates positions are generally identified for the epoch date of 1 January 1997 (generally represented in Units of years as 1997.0). To attain coordinate positions for another time, t, users require to apply the formula
X t X 1997.0 Vx t 1997.0
(0.31)
And same formulas are used for y(t) and z(t). Here, x(t) indicates the point‘s x- coordinate at time t, x(1997.0) presents the point‘s x-coordinate on date 1 January 1997, and vx presents the x-component of the point‘s velocity. National geodetic survey provides simple availability to the ITRF96 coordinate reference frame however a collection of more than 170 sites of the National continuously operating reference station (CORS) network. Coordinate positions, displacement rates, and other relevant data for these sites are accessible through the Internet by accessing: ftp://www.ngs.noaa. gov/cors/coord/coord_96. 4.7
Transforming Between Reference Frames In 1998, United States and Canadian officials both approved a Helmert transformation
to transform positional coordinates between ITRF96 and NAD 83 (CORS96). The IERS has also approved suitable Helmert transformations for transformation between ITRF96 and other ITRS reference frame realizations. NGS has programmed all these conversions into a software package, called HTDP (Hori-zontal Time-Dependent Positioning), which is 63
accessible through the Internet free of cost accessing NGS website. HTDP software allows persons to convert individual coordinate positions submitted interactively or a set of coordinate positions submitted as a formatted data file. In addition, if users willing to convert only a few coordinate positions, then they can run HTDP software interactively from this web page. As Helmert transformations, as programmed into HTDP software, are suitable for transforming coordinate positions between any two ITRS reference frame realizations or between any ITRS realization and NAD 83 (CORS96), more complex transformations are necessary. For transformations that include NAD 27, NAD 83 (1986), or NAD 83 (HARN). These difficulties occur because these reference frames include large regional and local deformations that cannot be measured by an easy Helmert transformation. For example, NAD 27 includes deformations at the 10 meter scale. That is, if any person used the finest likely Helmert transformation from NAD 27 to NAD 83 (CORS96), then the transformed NAD 27 coordinate positions may still be in uncertainty by as much as 10 m. In a similar manner, NAD 83 (1986) includes deformations at the 1 meter scale, and NAD 83 (HARN) includes deformations at the 0.1 m scale [41]. NGS has formed a software facility, known as NADCON, that exemplifies quite complex conversions to transform positional coordinates between any pair of the following coordinate reference frames: NAD 27, NAD 83 (1986), and NAD 83 (HARN). Mentioning to a reference frame pair of two dimensional grids that span the U.S.A, NADCON includes suitable measures for every grid node to convert its positional coordinates from one reference frame to another. Also, NADCON inserts these gridded measures to convert coordinate points situated within the grid‘s span. It must be noted that NADCON may be utilized only to change horizontal positional coordinates (latitude and longitude), because of ellipsoidal height comparative to NAD 27 or NAD 83 (1986) have never been accepted for most control points. As HTDP software may be utilized with pairs of particular reference frames (NAD 83 (CORS96), ITRF88, ITRF89…, and ITRF97) and NADCON software with pairs of other coordinate reference frames (NAD 27, NAD 83 (1986), and NAD 83 (HARN)), no national geodetic survey authorized software exists for transforming positional coordinates from any associate of one set to any affiliate of the other. In addition, no national geodetic survey authorized software present for converting NAD 83 (CORS93) or NAD 83 (CORS94) coordinate positions to other coordinate reference frames [42]. In case of WGS 84 coordinate reference system, it is usually supposed that WGS 84 coordinate system (original) is similar to NAD 83 (1986), and WGS 84 (G730) is similar to ITRF92, and that WGS 84 (G873) is 64
similar to ITRF96. Other conversions between reference frame pairs of the WGS 84 realizations, though, have also published in the literature [43].
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05 5.1
RESULT ANALYSIS OF SEISMIC DEVIATIONS
Introduction: A major earthquake of magnitude 7.9 on Monday June 23, 2014 at 20:53:09 UTC
occurred in a remote area of the volcanic Aleutian Islands. The epicentre (51.80°N 178.76°W) was located 19km (11miles) ESE of Little Sitkin Island, AlaskaThe June 23 earthquake resulted from oblique normal faulting at a depth of approximately 108 km. This is likely within the sub ducting Pacific Plate. At the location of this earthquake, the Pacific Plate sub ducts obliquely towards the northwest beneath the North American Plate at the rate of about 75mm/yr. Based on the geometry of the slab, and the relative movement of the tectonic plates, the slip vector is likely to have been oblique down-dip towards the ESE. The fault plane appears to be oblique, striking NW-SE and cutting steeply into the sub ducting slab. . It was the largest earthquake to occur in Alaska since the November 3, 2002 Denali Fault earthquake. The Alaska Earthquake Centre recorded over 2,500 aftershocks through end of the year. About 60 aftershocks had magnitudes of 4.0 or greater. The largest aftershock, magnitude 6.4 (smaller red star on the map), occurred about six hours after the main shock at 7:15 pm (June 24, 3:15 UTC). This aftershock was located at a much shallower depth (19 km or 12 miles) and outside of the main rupture zone of the 7.9 earthquake. This is the largest event to occur in the region since the magnitude 7.7 earthquakes on November 17, 2003, which occurred on the convergent boundary between the sub ducting Pacific and overriding North American crustal plates. Another major earthquake, M7.9, occurred farther east in 1996. This region, where the two plates are being forced directly into one another, is one of the world's most active seismic zones. Two great earthquakes occurred in this region, M8.7 Rat Islands earthquake in 1965 and M8.6 Andreanof Islands earthquake in 1957. These two earthquakes combined ruptured over half of the Aleutian mega thrust length. The magnitude 7.9 earthquake on June 23 is different from these mentioned ruptures on the Aleutian mega thrust. This earthquake was located at 118 km (73 miles) depth and was contained within the sub ducting Pacific plate (see cross-section below). This is the largest intra-slab earthquake ever recorded in Alaska. The next largest intra-slab earthquake, magnitude 7.3, was recorded on June 24, 2011 in Fox Islands at a depth of 74 km (46 miles). The AB21 CORS site is located in Adak city near Sitka, Alaska and it is installed in year 2006. The station ID for this CORS site is AB21. The monument type for this station is Shallow Drilled Braced Monument (SDBM) and the foundation for this monument is made up of steel rods, concrete block etc. The sample rate of Adak AB21 site is 15 seconds. Its IERS DOMES Number is A9 65
and CDP Number is A4. This CORS site is situated on North American tectonics plate. This CORS site use to precisely monitor tectonic movements and seismic phenomenon, since the time of its installation (2006). NGS used Trimble NETRS GNSS receiver for this CORS station. This GNSS receiver is compatible with GPS, GLONASS, GALILIEO, BDS, QZSS and satellite based augmentation systems. TRM29659.00 antenna type is used for this AB21 CORS site and antenna radome type is SCIT. Its antenna reference point (ARP) is BPA. The current NAD83 CORS position coordinates were found by reprocessing all NGS CORS data recorded from January 1994 to April 2011 in the NGS initial Multi-year CORS Solution (MYCS1) project. The assigned CORS position coordinates were published by National Geodetic Survey in September, 2011, and represent a new realisation known as NAD83 (2011), Epoch 2010.00. NGS revised position of this CORS site last time in December 2012 by using 57 days of data. The revised positional coordinates of AB21 CORS site in NAD_83 (EPOCH 2010) are
X 3940202.663 m latitude 51 51 50.95286 N Y 229769.094 m longitude 176 39 45.47428 W Z 4993529.401 m ellipsoid height 58.420 m The tectonic plate movement and seismic activities create significant deviation of CORS station from their assigned values. The North American tectonic plate is moving to the westsouthwest at about 2.3 cm (~1 inch) per year. The Adak AB21 CORS site is also displaced from its assigned positioning coordinates due North American tectonic plate movement and 23rd June 2014 Aleutian Islands earthquake. These deviations cause significant error especially in case of precise positioning. In the first part of this section we have a performance analysis of NGS AB21 CORS site and IU ADK ANSS seismic station (FBA ES-T EpiSensor Accelerometer), both sites recorded precise measurements of an earthquake occurred on 23rd of June 2014. The 24hr GPS observation data of Aleutian Islands earthquake recorded by AB21 CORS site is post processed by RTKLIB software by configuring RTKPOST for precise calculation of displacements due to seismic activities. This requires AB21 CORS site data with reliable position coordinates, precise satellite orbits, satellite clock corrections and antenna information. The AB21 CORS site data is available on NGS https://www.ngs.noaa.gov/CORS
and UNAVCO
https://www.unavco.org websites while other files like satellite ephemeris file, satellite clock correction file are available on TRKGET. The IU ADK ANSS seismic station data is 66
available on website of National Geodetic Survey and Centre for engineering Strong Motion Data (CESMD) http://strongmotioncenter.org/ . The Advanced National Seismic System (ANSS) is the United States national seismic network. When earthquakes hit, ANSS gives real-time data, offering latest information for emergency-response staff. In areas with plenty of seismic stations that data contains within small instances a Shake Map presenting the division of significantly damaging ground motion data utilized to focus after disaster response efforts. When completely applied, ANSS will offer such high seismic station coverage for all earthquake prone urban areas. Data from ANSS is solution inputs to the USGS National Seismic Hazard Maps, which assist people in earthquake-affected areas, construct secure building practices. The Centre for Engineering Strong Motion Data (CESMD) is a supportive centre established by the US Geological Survey (USGS) and the California Geological Survey (CGS) to incorporate earthquake strong-motion data from the CGS California Strong Motion Instrumentation Program, the USGS National Strong Motion plan, and the Advanced National Seismic System (ANSS). The CESMD offers raw and processed strong-motion data for earthquake engineering applications. The data recorded by IU ADK accelerometer includes displacement and velocity along three dimensions 90 degree component, 360 degree component and up component. The IU ADK recorded data is given for a certain time period. In this time period the earthquake achieved its maximum peak. For more precise computation of positional coordinates, the 60 days GPS data of the same CORS site is used. The GPS observation and navigation data files are in Receiver Independent Exchange Format (RINEX), and have 24hr static observation information. These GPS data files are post processed by Online Position User Service. OPUS allows users to submit their GPS data to NGS via website and post processed by using NGS computers and software (PAGES). This online post processing user facility provided by National Geodetic Survey enables us to achieve cm level accuracy. OPUS requires dual frequency GPS (L1/L2) fullwavelength carrier observables and static data of GNSS receiver. The second part of this section includes precise measurements of AB21 CORS site deviation due to North American tectonic plate movement by using GPS data files since the year 2006 (when this site was installed) to the ending dates of 2016. These GPS data files are also post processed by OPUS. The computations and simulations of these results calculate the North American plate precise movement along three axes. NGS did not revise positional coordinates of AB21 CORS after 2012 so the assigned positional coordinates currently available for all CORS sites did not include deviations due to tectonics movements and seismic activities. A performance analysis of Horizontal Time Depended Positioning software is also given, by comparing HTDP values 67
with AB21 CORS GPS data files during the year 2014. The comparison between HTDP measurements and AB21 CORS site observations during the year 2014 is used to estimate the differences with more precision between the measurements of these two platforms. The most recent modification of Horizontal Time Dependent Positioning software version 3.2.5 has been done on August, 30 2015. It only modifies corrections for minor rounding error inconsistencies. The last earthquake dislocation model incorporated into Horizontal Time Dependent Positioning software was 3rd November 2002 Denali earthquake. The present version of HTDP software includes a post seismic motion model only for Denali earthquake of 7.9 magnitudes that hit Central Alaska on 3rd of November 2002. The recent HTDP 3.2.5 software version model does not include position coordinates variation due to 23rd June 2014 Aleutian Islands earthquake. In this chapter the given precise measurements of AB 21 CORS site are helpful to revise its assigned positional coordinates which include all deviations due to interseismic, co seismic and post seismic activities. The GPS observations of AB21 position coordinates are also helpful to update HTDP measurements. To achieve this revision a precise assessment is done from the year 2012 to 2016 which includes all deviations due to tectonic movements and seismic activities. These assessments are also simulated for updated positional coordinates along three axes. In this assessment the difference between AB21 site observations from HTDP measurements due to 23rd June earthquake, inter-seismic, post-seismic and co-seismic activities are used to update HTDP estimations. 5.2 Performance Analysis of AB21 CORS Site and IU ADK Station for Precise Earthquake Measurement 5.2.1 Earthquake data recorded by AB21 CORS site The GPS observation data of 24 hr recorded AB21 CORS site on 23rd of June 2014 is used to investigate the variations in position coordinates of the same CORS site during this time period. This data is post processed with RTKLIB software by configuring RTKPOST. The GPS observation data file is in RINEX format. To achieve precise measurement of this earthquake, satellite navigation data file (n), precise satellite orbits (.sp3) file and for satellite clock correction information (.clk) files are used. The satellite navigation message file has information about satellite ephemeris i.e. information about satellite position and its orbit
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orientation. The SP3 format has been designed such that satellites other than GPS could be described as well. Antenna Exchange format (ANTEX) .atx file is used for antenna calibrations that provides models to correct for the antenna phase carrier variations. The position (.pos) file is used to plot variations in position coordinates of AB21 CORS site during the earthquake along three dimensions. The earthquake data recoded by AB21 CORS site is plotted with RTKPLOT, which clearly shows the deviation of the site during the earthquake from their assigned position coordinates. These plots present the deviation of AB21 CORS site along east-west, north-south and up-down axes. 5.2.2 Variations in AB21 CORS Site Position The plotted earthquake data by RTKPLOT presents the deviations of AB21 CORS site from its assigned position coordinates. The given below graph depicts the deviations of the site along three axes during 24hrs. The below graphical result clearly presents substantial deviations of the site during the earthquake along three dimensions. This graph also presents some other pre and post seismic activities recorded by AB21 site associated with the earthquake.
Time UTC (00:00 TO 24:00)hrs Figure 5.1 The Deviations (m) of AB21 CORS site from its assigned position coordinates
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5.2.3 Variations In AB21 CORS Site Velocity In the given graph the Adak AB21 CORS site shows zero velocity before the earthquake, however it presents variations in velocity during the earthquake. These variations also include some post seismic activities recorded by AB21 CORS site.
Time UTC (00:00 TO 24:00)hrs Figure 5.2 the velocity (m/s) variations of Adak AB21 CORS site RTKLIB software created a position (.pos) file from navigation(.n) and 24hr observation data file, to plot variations in position coordinates due to 23rd June 2014 earthquake. These variations are plotted by using RTKPLOT. This position file is converted into KML file with the help of RTKLIB. This KML file is used to display 24hr geographic data (23rd June 2014) recorded by AB21 CORS site, in an Earth browser such as Google Earth. The given below figures a,b,c specify the AB21 CORS site position while figure d, presents the deviations of AB21 CORS site during 24hrs on 23rd June 2014. These deviations are due to Aleutian Islands earthquake and some pre and post seismic activities. The given figures a,b,c indicate the position of AB21 CORS site by a red dot. In figure d there are many red dots that depict the deviations of AB21 site associated with 23rd June 2014 earthquake.
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Fig.5.3.a
Fig.5.3.b
Fig.5.3.c Fig.5.3 a,b,c The satellite images of Adak AB21 CORS site by using kml file
Figure 5.3.d The AB21 CORS site deviations during 24hr of 23rd June 2014 71
5.2.4 Earthquake data recorded by IU ADK Accelerometer The IU ADK ANSS seismic station recorded the data of 23rd June 2014 earthquake occurred in Aleutian Islands. The sensor is designed with wide bandwidths and linear high dynamic range for precise seismic measurements. This triaxial accelerometer has ability to record three components linear data motion however uniaxial accelerometer with high gain and short period is also helpful for fault line monitoring. The standardizing on Internet protocol (IP) is suggested for recorded data communication. The recorded strong motion data have continuous access to telemetry. The complete earthquake data can be obtained by substantial on site buffering or backup storage for the station. A consistent communication is achieved by error correction and packet retransmission which involves bidirectional communication. The maintenance and reliability issues involve two way communication and at least once a day State-Of-health messaging from instrument. This station has short packets and reasonably fast communication speed with negligible buffering delays i.e. less than 1 second transit time. The recorded data delivered from this station is consistent and appropriate for variety of communication technologies. The bandwidths for this station are 0.02 – 50 Hz. The low frequency requirement is based on scientific research works and the high frequency requirement is restricted by the effects over the distances. This accelerometer has adequate dynamic range and resolution. The site has capability to transmit old data meanwhile the current data is recorded without any interruption.
The IU ADK rd
Accelerometer recorded strong ground motion acceleration during the 23 June earthquake. This recorded acceleration is computer processed by CESMD and integrated to obtain the velocity and displacement records. As the earthquake forces vary so quickly during an earthquake that they have to be calculated many times as many as 200 in each second. IU ADK Accelerometer recorded the Aleutian Islands earthquake data during the time span of 89 seconds. In this time period earthquake represent maximum variations in earthquake magnitude. During this time period IU Accelerometer recorded 200 measurements in each second. The computer processed data consist of displacements and velocities along three dimensions. 5.2.5 Earthquake Displacement Variations Recorded By ADK IU Accelerometer In the given graphs the positive readings represent east, south and up directions while negative readings indicate west, north and down directions.
72
5.2.5 a
Displacement variations in East – West axis
Figure 5.4 Aleutian Islands earthquake displacement variations in east-west direction
5.2.5. b
Displacement variations in South-North axis
Figure 5.5. Aleutian Islands earthquake displacement variations in south-north direction
73
5.2.5. c Displacement variations in Up – Down axis
Figure 5.6 Aleutian Islands earthquake displacement variations in up-down direction
5.2.6 Earthquake Velocity Variations Recorded By ADK IU Accelerometer 5.2.6. a
Velocity variations in East – West axis
Figure 5.7 Aleutian Islands earthquake velocity variations in east-west direction
74
5.2.6. b
Velocity variations in South – North axis
Figure 5.8 Aleutian Islands earthquake velocity variations in south-north direction 5.2.6. c Velocity variations in Up – Down axis
Figure 5.9 Aleutian Islands earthquake velocity variations in up-down direction
75
The IU ADK Accelerometer has ability to monitor both small and infrequent events with high precision. The data recorded by it is useful for national and regional seismological research. This triaxial accelerometer recorded the variations of 23rd June 2014 earthquake data with high precision up to mm level accuracy. It has high resolution in the band 0.02 – 35 Hz with on scale recording. The IU ADK Accelerometer has sampling 200 sps to provide oversampling for better time resolution and to allow for transition bands of analog anti-alias filters. The IU ADK has short data latencies i.e. Less than 10s which is supportive for shake map generation and early warning applications. The resolutions are less than ambient noise in the 0.04 – 10 Hz. The IU ADK has features of on scale recording with high fidelity and also provides complete and continuous seismic data without any interruption. The above simulations depict that it recorded strong ground motion (Displacements and Velocities) with high precision. For the estimation of strong ground motion component the sensitivity in the band is 0.02 – 50 Hz. It has minimum clip level of 3.5 g, low hysteresis and constant absolute sensitivity. The Aleutian Islands earthquake is recorded by IU ADK Accelerometer with 200 sps. The AB21 CORS site also recorded this earthquake; however the sample rate of this CORS site is 15 second. As the seismic forces changes so rapidly and they should be calculated at least 200 samples per second and AB21 CORS does not measure changes that rapid. The CORS site is best to find the final location after the earthquake. 5.3 Precise Measurement of AB21 CORS Site Deviation From Assigned Coordinates Due To Aleutian Islands Earthquake 5.3.1 60 Days post seismic data recorded by AB21 CORS Site NGS reviewed the published (Official) NAD_83 position and velocities for a particular CORS site if one or more of the following situations occur, the antenna at CORS has been replaced, the position of CORS changed due to nearby earthquake or due to an error discovered during the computation of CORS position/velocity. NGS revised NAD 83 position coordinates for reference epoch 2010 in December 2012. The NGS used 57 days of GPS data for position coordinate revision of AB21 CORS site. The revised positional coordinates for AB21 CORS site in NAD_83 (EPOCH 2010) are:
X 3940202.663 m latitude 51 51 50.95286 N Y 229769.094 m longitude 176 39 45.47428 W Z 4993529.401 m ellipsoid height 58.420 m
76
Due to North American Tectonic plate movement and earth crustal displacement associated with 23rd June 2014 Aleutian Islands earthquake, the AB21 CORS site substantially deviated from their assigned position coordinates. To update these position coordinates, a precise estimation of CORS site deviation associated with seismic activities is required. For this purpose a 60 days post seismic data is used for the precise estimation of AB21 CORS site deviation due to Aleutian Islands earthquake(23rd of June 2014). These GPS observation data files are available on National Geodetic Survey (www.ngs.noaa.gov/UFCORS) and UNAVO www.unavco.org websites. These GPS data files are in RINEX format. This RINEX observation data file is post processed by Online Position User Service (OPUS) to achieve cm level accuracy. A three dimensional displacement is determined associated with this earthquake (23rd of June 2014) at AB21 CORS site located in Alaska. The post earthquake positional coordinates are computed by using GPS data monitored for 60 days that begins 07 day (1st of July 2014) following the earthquake. Hence the computed displacements for AB21 CORS site may include some post seismic motions. A 24 hours GPS observation data for each day is used for precise monitoring. 5.3.2 Monitoring of AB21 CORS Site Deviation Along x-axis The variations in AB21 CORS NAD_83 (2010) x-axis position coordinate with respect to the published value in ECEF Cartesian coordinate system spanning a time period of 60 days are recorded and plotted. These results determined the differences of -4.0cm to 4.3cm in AB21 x-axis NAD_83 position coordinate from its adopted value. The given data includes permanent deviation of AB21 CORS site with some variable post seismic motions. Table.5.1 60 days post seismic data of AB21 CORS site of x-axis coordinate
182
AB21 CORS measurements x-axis Coordinate (m) -3940202.622
183
-3940202.623
-4.00
184
-3940202.622
-4.1
185
-3940202.622
-4.1
186
-3940202.621
-4.2
Year 2014 (Days)
77
AB21 CORS Displacement x (cm) -4.1
187
-3940202.621
-4.2
188
-3940202.622
-4.1
189
-3940202.621
-4.2
190
-3940202.623
-4.00
191
-3940202.622
-4.1
192
-3940202.623
-4.00
193
-3940202.622
-4.1
194
-3940202.621
-4.2
195
-3940202.621
-4.2
196
-3940202.622
-4.1
197
-3940202.623
-4.00
198
-3940202.622
-4.1
199
-3940202.621
-4.2
200
-3940202.620
-4.3
201
-3940202.622
-4.1
202
-3940202.620
-4.3
203
-3940202.622
-4.1
204
-3940202.621
-4.2
205
-3940202.622
-4.1
206
-3940202.621
-4.2
207
-3940202.620
-4.3
208
-3940202.621
-4.2
209
-3940202.622
-4.1
210
-3940202.621
-4.2
211
-3940202.622
-4.1
212
-3940202.620
-4.3
213
-3940202.622
-4.1
214
-3940202.620
-4.3
215
-3940202.620
-4.3
216
-3940202.621
-4.2
217
-3940202.620
-4.3
218
-3940202.621
-4.2
78
219
-3940202.622
-4.1
220
-3940202.622
-4.1
221
-3940202.622
-4.1
222
-3940202.620
-4.3
223
-3940202.622
-4.1
224
-3940202.622
-4.1
225
-3940202.621
-4.2
226
-3940202.622
-4.1
227
-3940202.622
-4.1
228
-3940202.621
-4.2
229
-3940202.621
-4.2
230
-3940202.622
-4.1
231
-3940202.622
-4.1
232
-3940202.621
-4.2
233
-3940202.623
-4.00
234
-3940202.622
-4.1
235
-3940202.622
-4.1
236
-3940202.622
-4.1
237
-3940202.620
-4.3
238
-3940202.620
-4.3
239
-3940202.622
-4.1
240
-3940202.622
-4.1
241
-3940202.621
-4.2
The figure.5.10 depicts the difference between the published and computed positional coordinates during the 60 days, preceding day 241 of 2014 for CORS station Adak AB21. It represents the maximum displacement of -4.3cm and minimum measurement of -4.0cm along x-axis during the 60 days time span.
79
AB21 CORS site deviation along x-axis (cm) -3.95
Displacement (cm)
-4
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
-4.05 -4.1 -4.15 -4.2 -4.25 -4.3 -4.35
Days 2014 after Earthquake
Figure 5.10 AB21 CORS site post seismic measurements along x-axis 5.3.3 Monitoring of AB21 CORS Site Deviation Along y-axis The recorded y-axis NAD_83 position coordinate measurements are used to estimate the deviation of AB21 site from its assigned y-axis NAD_83 (2010) positional coordinate. The results show the deviation of -3.0 to -3.3cm. The given 60 days GPS data begins 182 day of 2014 for Adak AB21 CORS. The given GPS data determined the lasting deviation with some seismic motions after the earthquake. Table.5.2 60 days post seismic data of AB21 CORS site of y-axis coordinate
182
AB21 CORS measurements y-axis Coordinate(m) -229769.062
183
-229769.062
-3.2
184
-229769.063
-3.1
185
-229769.062
-3.2
186
-229769.063
-3.1
187
-229769.062
-3.2
188
-229769.062
-3.2
189
-229769.063
-3.1
190
-229769.062
-3.2
Year 2014 (Days)
80
AB21 CORS Displacement y (cm) -3.2
191
-229769.062
-3.2
192
-229769.061
-3.3
193
-229769.062
-3.2
194
-229769.061
-3.3
195
-229769.061
-3.3
196
-229769.063
-3.1
197
-229769.061
-3.3
198
-229769.061
-3.3
199
-229769.062
-3.2
200
-229769.061
-3.3
201
-229769.062
-3.2
202
-229769.062
-3.2
203
-229769.061
-3.3
204
-229769.063
-3.1
205
-229769.063
-3.1
206
-229769.062
-3.2
207
-229769.061
-3.1
208
-229769.063
-3.1
209
-229769.063
-3.1
210
-229769.062
-3.2
211
-229769.062
-3.2
212
-229769.062
-3.2
213
-229769.062
-3.2
214
-229769.062
-3.2
215
-229769.062
-3.2
216
-229769.062
-3.2
217
-229769.062
-3.2
218
-229769.062
-3.2
219
-229769.063
-3.1
220
-229769.062
-3.2
221
-229769.063
-3.1
222
-229769.063
-3.1
81
223
-229769.064
-3.00
224
-229769.064
-3.00
225
-229769.063
-3.1
226
-229769.062
-3.2
227
-229769.062
-3.2
228
-229769.062
-3.2
229
-229769.062
-3.2
230
-229769.062
-3.2
231
-229769.062
-3.2
232
-229769.062
-3.2
233
-229769.062
-3.2
234
-229769.062
-3.2
235
-229769.062
-3.2
236
-229769.064
-3.00
237
-229769.063
-3.1
238
-229769.063
-3.1
239
-229769.064
-3.00
240
-229769.064
-3.00
241
-229769.063
-3.1
The Figure.5.11 represents the deviation of this CORS site from adopted y-axis NAD_83 (2010) coordinate due to 23rd of June 2014 Aleutian Islands earthquake. The graphical presentation shows that the maximum displacement along y-axis is -3.3cm while the minimum deviation is -3.0cm. These variations in measurements are due to post seismic motions.
82
AB21 CORS site deviation along y-axis (cm) -2.95
Displacement (cm)
-3
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
-3.05 -3.1 -3.15 -3.2 -3.25 -3.3 -3.35
Days 2014 after Earthquake
Figure 5.11 AB21 CORS site post seismic measurements along y-axis 5.3.4 Monitoring of AB21 CORS Site Deviation Along z-axis The given below data represents the AB21 NAD_83 z-axis position coordinates displacement from published NAD_83 (2010) value. These variations include both permanent deviation due to earthquake and other post seismic motions. These variations due to post seismic motion are from 1.7cm to 1.9cm. Table.5.3 60 days post seismic data of AB21 CORS site of z-axis coordinate
182
AB21 CORS measurements z-axis Coordinate (m) 4993529.420
183
4993529.420
1.9
184
4993529.419
1.8
185
4993529.420
1.9
186
4993529.420
1.9
187
4993529.418
1.7
188
4993529.420
1.9
189
4993529.419
1.8
190
4993529.419
1.8
191
4993529.420
1.9
Year 2014 (Days)
83
AB21 CORS Displacement z (cm) 1.9
192
4993529.419
1.8
193
4993529.419
1.8
194
4993529.419
1.8
195
4993529.420
1.9
196
4993529.420
1.9
197
4993529.419
1.8
198
4993529.420
1.9
199
4993529.420
1.9
200
4993529.419
1.8
201
4993529.419
1.8
202
4993529.419
1.8
203
4993529.418
1.7
204
4993529.419
1.8
205
4993529.419
1.8
206
4993529.418
1.7
207
4993529.420
1.9
208
4993529.420
1.9
209
4993529.420
1.9
210
4993529.418
1.7
211
4993529.420
1.9
212
4993529.419
1.8
213
4993529.419
1.8
214
4993529.419
1.8
215
4993529.419
1.8
216
4993529.419
1.8
217
4993529.419
1.8
218
4993529.420
1.9
219
4993529.419
1.8
220
4993529.419
1.8
221
4993529.419
1.8
222
4993529.420
1.9
223
4993529.420
1.9
84
224
4993529.418
1.7
225
4993529.420
1.9
226
4993529.419
1.8
227
4993529.419
1.8
228
4993529.419
1.8
229
4993529.419
1.8
230
4993529.419
1.8
231
4993529.419
1.8
232
4993529.419
1.8
233
4993529.419
1.8
234
4993529.419
1.8
235
4993529.419
1.8
236
4993529.419
1.8
237
4993529.420
1.9
238
4993529.420
1.9
239
4993529.420
1.9
240
4993529.420
1.9
241
4993529.419
1.8
The Figure.5.12 predicts the maximum deviation of 1.9cm and minimum displacement of 1.7cm of AB21 CORS z-axis NAD_83 (2010) position coordinates from assigned value.
85
AB21 CORS site deviation along z-axis (cm) 1.95
Displacement (cm)
1.9 1.85 1.8 1.75 1.7 1.65 0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
Days 2014 after Earthquake
Figure 5.12 AB21 CORS site post seismic measurements along z-axis It is important to note that during this 60 days time period the archives at Adak AB21 showed that antenna was not replaced or moved by the AB21 CORS site operators. In case of any replacement or change by the CORS site operators without notifying NGS, there appears to be a negative bias of 1cm along vertical component that originally could be attributed to this particular reason. 5.4
AB21 CORS Site Deviation Due to Tectonic Motion (2006-2016) GNSS is the most advanced tool to track tectonic plate movement with high accuracy.
GNSS is very useful to determine both displacement and velocity of tectonic plate. AB21 CORS site is located on highly active seismic zone. This CORS site is situated on North American tectonic plate, near to convergent boundaries of North American plate and Pacific plate. Adak AB21 CORS site was installed on year 2006. To monitor Adak AB21 CORS site deviation from its assigned NAD_83 positional coordinates at the time of CORS site installation, GPS observations for the months of January, March, June and September of each year since 2006 are recorded. These recorded GPS data observation files of AB21 CORS site are in rinex format and post processed by using OPUS. 5.4.1 Monitoring of AB21 CORS site deviation along x-axis The given GPS observations in the below table represent that the AB21 CORS site is displacing from adopted NAD_83 x-axis position coordinate with the rate of -0.1 to 0.2cm/year. These GPS measurements represent the deviation of AB21 CORS site with the same rate since 2006 to the beginning of 2014. In June 2014 there is a significant deviation of 86
nearly -4.0 cm along x-axis. This is due to the 23rd June 2014 Aleutian Islands earthquake. The last reading of January 2017 shows that AB21 CORS site is displaced by -5.2cm from its assigned value of NAD_83 x-axis position coordinates 2006. Table.5.4 AB21 CORS site deviation along x-axis since 2006
2006.1
AB21 CORS x-axis Coordinate measurement (m) -3940202.671
AB21 CORS site Deviation along x-axis (cm) 0
2006.3
-3940202.671
0
2006.6
-3940202.670
-0.1
2006.9
-3940202.670
-0.1
2007.1
-3940202.669
-0.2
2007.3
-3940202.669
-0.2
2007.6
-3940202.668
-0.3
2007.9
-3940202.668
-0.3
2008.1
-3940202.668
-0.3
2008.3
-3940202.668
-0.3
2008.6
-3940202.667
-0.4
2008.9
-3940202.667
-0.4
2009.1
-3940202.667
-0.4
2009.3
-3940202.667
-0.4
2009.6
-3940202.666
-0.5
2009.9
-3940202.666
-0.5
2010.1
-3940202.666
-0.5
2010.3
-3940202.666
-0.5
2010.6
-3940202.665
-0.6
2010.9
-3940202.665
-0.6
2011.1
-3940202.665
-0.6
2011.3
-3940202.664
-0.7
2011.6
-3940202.664
-0.7
2011.9
-3940202.664
-0.7
Years
87
2012.1
-3940202.664
-0.7
2012.3
-3940202.664
-0.7
2012.6
-3940202.663
-0.8
2012.9
-3940202.663
-0.8
2013.1
-3940202.663
-0.8
2013.3
-3940202.662
-0.9
2013.6
-3940202.662
-0.9
2013.9
-3940202.662
-0.9
2014.1
-3940202.662
-0.9
2014.3
-3940202.662
-0.9
2014.6
-3940202.661
-4.7
2014.9
-3940202.623
-4.8
2015.1
-3940202.622
-4.9
2015.3
-3940202.622
-4.9
2015.6
-3940202.621
-5.00
2015.9
-3940202.621
-5.00
2016.1
-3940202.620
-5.1
2016.3
-3940202.620
-5.1
2016.6
-3940202.619
-5.2
2016.9
-3940202.619
-5.2
2017.1
-3940202.619
-5.2
The Figure.5.13 depicts the deviation of the AB21 CORS site along x-axis from assigned positional coordinates due to North American tectonic plate movement and Aleutian Islands earthquake.
88
AB21 CORS site Deviation along x-axis (cm)
Displacement (cm)
1 0 2004 -1
2006
2008
2010
2012
2014
2016
2018
-2 -3
-4 -5 -6
Years
Figure. 5.13 AB21 CORS site deviation due to tectonic plate movement along x-axis 5.4.2 Monitoring of AB21 CORS Site Deviation Along y-axis The given below are the GPS observations for NAD_83 y-axis position coordinate of AB21 CORS site. These measurements represent that this CORS site is deviating with the rate of 3.0 to 4.0mm/year along y-axis. The measurement of June 2014 represents the sudden displacement of approximately 3.0 cm towards negative y-axis. The last observation of January 2017 of AB21 CORS site shows the deviation of 7mm from it assigned NAD_83 yaxis position coordinates at the time of its installation 2006. Table.5.5 AB21 CORS site deviation along y-axis since 2006 AB21 CORS y-axis
AB21 CORS Deviation
Coordinate measurement (m)
along y-axis (cm)
2006.1
-229769.067
0
2006.3
-229769.067
0
2006.6
-229769.070
0.3
2006.9
-229769.072
0.5
2007.1
-229769.073
0.7
2007.3
-229769.074
0.7
2007.6
-229769.075
0.8
2007.9
-229769.076
0.9
Years
89
2008.1
-229769.077
1.00
2008.3
-229769.078
1.1
2008.6
-229769.079
1.2
2008.9
-229769.079
1.2
2009.1
-229769.080
1.3
2009.3
-229769.081
1.4
2009.6
-229769.082
1.5
2009.9
-229769.083
1.6
2010.1
-229769.084
1.7
2010.3
-229769.085
1.8
2010.6
-229769.085
1.8
2010.9
-229769.086
1.9
2011.1
-229769.087
2.00
2011.3
-229769.087
2.00
2011.6
-229769.088
2.1
2011.9
-229769.089
2.2
2012.1
-229769.090
2.3
2012.3
-229769.091
2.4
2012.6
-229769.092
2.5
2012.9
-229769.093
2.6
2013.1
-229769.094
2.7
2013.3
-229769.095
2.8
2013.6
-229769.096
2.9
2013.9
-229769.097
3.00
2014.1
-229769.098
3.1
2014.3
-229769.098
3.1
2014.6
-229769.099
0.1
2014.9
-229769.069
0.2
2015.1
-229769.071
0.4
2015.3
-229769.071
0.4
2015.6
-229769.072
0.5
2015.9
-229769.072
0.5
90
2016.1
-229769.073
0.6
2016.3
-229769.073
0.6
2016.6
-229769.074
0.7
2016.9
-229769.074
0.7
2017.1
-229769.074
0.7
The figure.5.14 shows the variation of AB21 CORS y-axis position coordinate measurements due to North American plate movement and displacement of site due to Aleutian Islands earthquake.
AB21 CORS site Deviation along y-axis (cm) 3.5
Displacement (cm)
3 2.5 2 1.5
1 0.5 0 2004 -0.5
2006
2008
2010
2012
2014
2016
2018
Years
Figure 5.14 AB21 CORS site deviation due to tectonic plate movement along y-axis 5.4.3 Monitoring of AB21 CORS Site Along z-axis The GPS observations for NAD_83 z-axis position coordinate of AB21 CORS site are given in the table. These GPS measurements represent that the AB21 CORS site is deviating at the rate of -0.1 to -0.2cm/year along z-axis. The negative values show that the site is moving in opposite direction with this rate. The measurement of June 2014 represents the displacement of approximately 1.8cm along z-axis from assigned values. The final reading of January 2017 of AB21 CORS site shows the deviation of -4mm from its assigned NAD_83 zaxis position coordinates since 2006.
91
Table.5.6 AB21 CORS site deviation along z-axis since 2006 AB21 CORS z-axis
AB21 CORS site Deviation
Coordinate measurement (m)
along z-axis (cm)
2006.1
4993529.420
0
2006.3
4993529.419
0
2006.6
4993529.418
-0.2
2006.9
4993529.417
-0.3
2007.1
4993529.416
-0.4
2007.3
4993529.416
-0.4
2007.6
4993529.415
-0.5
2007.9
4993529.413
-0.6
2008.1
4993529.413
-0.6
2008.3
4993529.412
-0.7
2008.6
4993529.412
-0.7
2008.9
4993529.411
-0.8
2009.1
4993529.411
-0.8
2009.3
4993529.410
-0.9
2009.6
4993529.410
-0.9
2009.9
4993529.409
-1.00
2010.1
4993529.409
-1.00
2010.3
4993529.408
-1.1
2010.6
4993529.408
-1.1
2010.9
4993529.407
-1.2
2011.1
4993529.407
-1.2
2011.3
4993529.407
-1.2
2011.6
4993529.406
-1.3
2011.9
4993529.406
-1.3
2012.1
4993529.406
-1.3
2012.3
4993529.405
-1.4
2012.6
4993529.404
-1.5
2012.9
4993529.404
-1.5
Years
92
2013.1
4993529.403
-1.6
2013.3
4993529.402
-1.7
2013.6
4993529.402
-1.7
2013.9
4993529.401
-1.8
2014.1
4993529.401
-1.8
2014.3
4993529.400
-1.9
2014.6
4993529.399
-0.1
2014.9
4993529.418
-0.2
2015.1
4993529.419
-0.1
2015.3
4993529.418
-0.2
2015.6
4993529.418
-0.2
2015.9
4993529.417
-0.3
2016.1
4993529.417
-0.3
2016.3
4993529.417
-0.3
2016.6
4993529.416
-0.4
2016.9
4993529.416
-0.4
2017.1
4993529.416
-0.4
The Figure.5.15 describes the deviation of AB21 CORS site due to north American tectonic plate movement and displacement due to 23rd June 2014 earthquake.
AB21 CORS site Deviation along z-axis (cm) Displacement (cm)
0.5 0 2004
2006
2008
2010
2012
2014
2016
2018
-0.5 -1 -1.5 -2 -2.5
Years
Figure 5.15 AB21 CORS site deviation due to tectonic plate movement along z-axis 93
5.5
Performance Analysis of HTDP Software with AB21 CORS Data of Year 2014 This section describes the deviations of AB21 CORS site from its assigned position
coordinates along three axes during the year of 2014 due to seismic activities. These recorded GPS measurements compared with the computed position coordinates readings of the Horizontal Time Dependent Positioning software. The present model of HTDP software only includes post seismic deviations due to 2003 Denali earthquake. This model offers amplitudes Ai,j(φ,λ) at the nodes of a two dimensional rectangular grid(LAT, LONG). The present version of HTDP software 3.2.5 doesn‘t include any seismic, co seismic and post seismic activities associated with 23rd June 2014 earthquake. The difference between assigned and observed position coordinates of AB21 CORS increased significantly after the 23rd June 2014 Aleutian Islands earthquake. Similarly the difference between HTDP 3.2.5 software computations and AB21 CORS site GPS measurements get larger due to earthquake. The updated position coordinates in latest HTDP 3.2.5 model of Adak AB21 CORS site position differ with observed GPS measurements in three dimensions. The given data of year 2014 consist of AB21 CORS position coordinate measurements and HTDP coordinates measurements with their variations from assigned NAD_83 (epoch 2010) position coordinates 2012. The recorded GPS observation files are in RINEX format. These observation files are post processed by Online Position User Service (OPUS). These measurements are used to precisely estimate the difference of HTDP software computed values with GPS observations. This comparison is useful to update recent model of HTDP software by including all precisely estimated positioning coordinates‘ differences due to Aleutian Island earthquake. The specified reference frames to compute HTDP software measurements is NAD_83 (2011/CORS96/2007) North American plate fixed. The HTDP software output values are dependent on specified reference frame. These computed values vary with the change of input specifications. 5.5.1 HTDP software and AB21 CORS site measurements along x-axis In case of Horizontal Time Dependent Positioning software, the position coordinate‘s measurements represent -2 mm/yr deviation of North American Tectonic plate. Due to this tectonic plate deviation AB21 CORS site is deviating from its assigned coordinates. The given below data has variations along x-axis positioning coordinate throughout the year of 94
2014. It is clearly observed that the HTDP software does not include earth crustal displacement due to the seismic activities associated with 23rd June 2014 in Aleutians islands Alaska. The observations computed by both HTDP software and AB21 CORS site are in good agreement till 23rd June, however there is a difference of 4.1cm between these measurements. AB21 CORS site recorded the earth crustal displacement due to the Aleutian Islands earthquake but HTDP software grid position coordinates for this region are not updated after this seismic event. Table.5.7 HTDP software and AB21 CORS site data of x-coordinate during year 2014 Year 2014 (Days)
HTDP x-axis Coordinate measurements (m)
CORS x-axis Coordinate measurements (m)
-3940202.659
HTDP Computed Deviation (x) cm -0.2
-3940202.659
CORS site recorded Deviation (x)cm -0.2
1 15
-3940202.659
-0.2
-3940202.660
-0.1
30
-3940202.659
-0.2
-3940202.660
-0.1
45
-3940202.659
-0.2
-3940202.659
-0.2
60
-3940202.659
-0.2
-3940202.659
-0.2
75
-3940202.659
-0.2
-3940202.660
-0.1
90
-3940202.659
-0.2
-3940202.659
-0.2
105
-3940202.659
-0.2
-3940202.659
-0.2
120
-3940202.659
-0.2
-3940202.659
-0.2
135
-3940202.659
-0.2
-3940202.659
-0.2
150
-3940202.659
-0.2
-3940202.659
-0.2
165
-3940202.659
-0.2
-3940202.659
-0.2
180
-3940202.659
-0.2
-3940202.618
-4.3
195
-3940202.659
-0.2
-3940202.619
-4.3
210
-3940202.659
-0.2
-3940202.619
-4.2
225
-3940202.659
-0.2
-3940202.619
-4.2
240
-3940202.659
-0.2
-3940202.622
-3.9
255
-3940202.659
-0.2
-3940202.620
-4.1
270
-3940202.659
-0.2
-3940202.620
-4.1
285
-3940202.658
-0.3
-3940202.620
-4.1
300
-3940202.658
-0.3
-3940202.620
-4.1
95
315
-3940202.658
-0.3
-3940202.620
-4.1
330
-3940202.658
-0.3
-3940202.620
-4.1
345
-3940202.658
-0.3
-3940202.620
-4.1
360
-3940202.658
-0.3
-3940202.620
-4.1
The figure.5.16 depicts the variations along x-axis position coordinate of AB21 CORS site during 360 days of year 2014. The graph shows the sharp variation in measurements due Aleutian Islands seismic activity. This earthquake produced a displacement of 4.1cm from adopted position coordinates.
AB21 CORS site deviation along x-axis
Displacement (cm)
1 0 0
25
50
75
100 125 150 175 200 225 250 275 300 325 350 375 400
-1 -2 -3 -4 -5
Year 2014 Figure 5.16 AB21 CORS site deviation along x-axis during year 2014
Fig.5.17 shows the deviation computed by HTDP software along x-axis position coordinates measurements i.e. only -1mm due to North American tectonic plate movement during 2014.
96
HTDP computed Deviation along x-axis
0
Displacement (cm)
-0.05
0
25
50
75
100 125 150 175 200 225 250 275 300 325 350 375 400
-0.1
-0.15 -0.2 -0.25 -0.3 -0.35
Year 2014
Figure 5.17 HTDP software measurements along x-axis during year 2014 The Fig.5.18 represents the comparison between HTDP software and AB21 CORS site measurements. This graphical presentation clearly shows the difference of 4.1cm between HTDP software readings and CORS measurements. 1
Comparison of measurements along x-axis 0
Displacement (cm)
0
25
50
75
100 125 150 175 200 225 250 275 300 325 350 375 400
-1 CORS Deviation (X)cm
-2 HTDP Computed Deviation (X) cm
-3 -4 -5
Year 2014
Figure 5.18 the comparison between AB21 CORS site and HTDP deviation along x-axis during year 2014 5.5.2 HTDP software and AB21 CORS Site measurements along y-axis The Horizontal Time Dependent Positioning software computed the deviation of 3mm/yr for North American Tectonic plate along y- axis. This tectonic plate deviation also caused the displacement of AB21 CORS site from its assigned y- position coordinates. The given below data has displacement variations along y-axis positioning coordinate throughout 97
the year of 2014. It is clearly noted that the HTDP software does not include earth crustal displacement along y-axis associated with earthquake of 23rd June 2014 in Aleutians Islands Alaska. The deviation measurements estimated by both HTDP software and AB21 CORS site are similar before the earthquake; however after this seismic activity the HTDP software shows the displacement of 0.8cm and the deviation of AB21 CORS site is -3.2cm. The difference in these observations is because of AB21 CORS site recorded both the earth crustal displacement and North American tectonic plate motion while the HTDP 3.2.5 software position coordinates for this grid of North American tectonic plate are not updated after this seismic event. Table.5.8 HTDP software and AB21 CORS site data of y-coordinate during year 2014 HTDP y-axis
HTDP
CORS y-axis
CORS site
Coordinate
Computed
Coordinate
recorded Deviation
measurements (m)
Deviation (y) cm
measurements (m)
(y)cm
1
-229769.102
0.7
-229769.102
0.7
15
-229769.102
0.7
-229769.101
0.6
30
-229769.102
0.7
-229769.102
0.7
45
-229769.102
0.7
-229769.102
0.7
60
-229769.102
0.7
-229769.102
0.7
75
-229769.102
0.7
-229769.102
0.7
90
-229769.102
0.7
-229769.102
0.7
105
-229769.103
0.8
-229769.102
0.7
120
-229769.103
0.8
-229769.103
0.8
135
-229769.103
0.8
-229769.103
0.8
150
-229769.103
0.8
-229769.103
0.8
165
-229769.103
0.8
-229769.103
0.8
180
-229769.103
0.8
-229769.063
-3.2
195
-229769.103
0.8
-229769.064
-3.1
210
-229769.103
0.8
-229769.063
-3.2
225
-229769.103
0.8
-229769.064
-3.1
Year 2014 (Days)
98
240
-229769.103
0.8
-229769.064
-3.1
255
-229769.103
0.8
-229769.065
-3
270
-229769.103
0.8
-229769.065
-3
285
-229769.104
0.9
-229769.065
-3
300
-229769.104
0.9
-229769.067
-2.8
315
-229769.104
0.9
-229769.067
-2.8
330
-229769.104
0.9
-229769.067
-2.8
345
-229769.104
0.9
-229769.068
-2.7
360
-229769.104
0.9
-229769.068
-2.7
Fig.5.19 represents a substantial deviation of AB21 CORS site towards negative y axis. This figure also depicts the North American tectonic plate motion during the year 2014. The CORS site AB21 is deviated approximately 4cm from assigned positioning coordinates along y-axis.
AB21 CORS site Deviation along y-axis Displacement (cm)
2 1 0 0
25
50
75
100 125 150 175 200 225 250 275 300 325 350 375 400
-1 -2 -3 -4
Year 2014 Figure 5.19 AB21 CORS site deviation along Y-axis during year 2014
Fig.5.20 shows that the HTDP software is not updated according to seismic activities after 23rd June 2014 earthquake.These measurements contain only deviation due to tectonic plate movement.
99
Displacement (cm)
HTDP Computed Deviation along y-axis 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0
25
50
75
100 125 150 175 200 225 250 275 300 325 350 375 400
Year 2014 Figure 5.20 HTDP software measurements along y-axis during year 2014 In Fig.5.21 it can be observe that the HTDP software are not compatible with the post processed measurements of AB21 CORS site. 2
Comparison of measurements along y-axis
Displacement (cm)
1
0 0
25
50
75
100 125 150 175 200 225 250 275 300 325 350 375 400
-1
CORS Deviation (Y)cm
-2
HTDP Computed Deviation (Y) cm
-3
-4
Year 2014
Figure 5.21 Comparison between AB21 CORS site and HTDP deviation along y-axis during year 2014 5.5.3 HTDP software and AB21 CORS Site measurements along z-axis The Horizontal Time Dependent Positioning software computed the deviation of 2mm/yr for North American Tectonic plate along z-axis. This tectonic plate deviation also caused the displacement of AB21 CORS site from its assigned z-axis positioning coordinates. The given below data has displacement variations along z-axis positioning coordinate during 100
360 days of year 2014. It is clearly observed from the measurements that the HTDP software does not include earth crustal displacement along z-axis axis associated Aleutian Islands earthquake of 23rd June 2014. The displacement measurements calculated by both HTDP software and AB21 CORS site are close before the Aleutian Islands earthquake; however after this seismic activity the HTDP software has the displacement of -0.6cm and the deviation of AB21 CORS site is 1.9cm from their assigned values. The difference in these measurements is because of AB21 CORS site recording both the earth crustal displacement and North American tectonic plate motion, while the HTDP software z-axis position coordinates for this particular grid of North American tectonic plate are not updated after this seismic event. Table.5.9 HTDP software and AB21 CORS site data of z-coordinate during year 2014 Year 2014 (Days)
HTDP Z-axis Coordinate measurements (m)
CORS Z-axis Coordinate measurements (m)
4993529.394
HTDP Computed Deviation (z)cm -0.4
4993529.393
CORS site recorded Deviation (z)cm -0.5
1 15
4993529.394
-0.4
4993529.393
-0.5
30
4993529.394
-0.4
4993529.393
-0.5
45
4993529.394
-0.4
4993529.393
-0.5
60
4993529.393
-0.5
4993529.393
-0.5
75
4993529.393
-0.5
4993529.393
-0.5
90
4993529.393
-0.5
4993529.393
-0.5
105
4993529.393
-0.5
4993529.393
-0.5
120
4993529.393
-0.5
4993529.393
-0.5
135
4993529.393
-0.5
4993529.395
-0.3
150
4993529.393
-0.5
4993529.394
-0.4
165
4993529.393
-0.5
4993529.394
-0.4
180
4993529.392
-0.6
4993529.42
1.9
195
4993529.392
-0.6
4993529.419
1.8
210
4993529.392
-0.6
4993529.420
1.9
225
4993529.392
-0.6
4993529.420
1.9
240
4993529.392
-0.6
4993529.420
1.9
255
4993529.392
-0.6
4993529.420
1.9
101
270
4993529.392
-0.6
4993529.419
1.8
285
4993529.392
-0.6
4993529.419
1.8
300
4993529.391
-0.7
4993529.419
1.8
315
4993529.391
-0.7
4993529.418
1.7
330
4993529.391
-0.7
4993529.418
1.7
345
4993529.391
-0.7
4993529.418
1.7
360
4993529.391
-0.7
4993529.418
1.7
The Fig.5.22 depicts a significant change in position coordinates of AB21 CORS site along zaxis. This substantial deviation of approximately 2.3cm is due major seismic activity of Aleutian Islands.
AB21 CORS site Deviation along z-axis Displacement (cm)
2.5 2 1.5 1 0.5 0 0
25
50
75
100 125 150 175 200 225 250 275 300 325 350 375 400
-0.5 -1
Year 2014 Figure 5.22 AB21 CORS site deviation along z-axis during year 2014
Fig.5.23 represents the North American tectonic plate movement along z-axis. These measurements show that this tectonic plate is deviating with rate of -2mm/yr. The given below graph also represents that the earthquake deviations are not included in HTDP software measurements.
102
HTDP Computed Deviation along z-axis 0
Displacement (cm)
-0.1
0
25
50
75
100 125 150 175 200 225 250 275 300 325 350 375 400
-0.2 -0.3 -0.4
-0.5 -0.6
-0.7 -0.8
Year 2014 Figure 5.23 HTDP software measurements along z-axis during year 2014
Fig.5.24 represents that HTDP software computations are out of agreement with AB21 CORS site GPS measurements after the earthquake. 2.5
Comparison of measurements along z-axis
Displacement (cm)
2 1.5
CORS Deviation (z)cm
1
HTDP Computed Deviation (z)cm
0.5 0 0
25
50
75
100 125 150 175 200 225 250 275 300 325 350 375 400
-0.5 -1
Year 2014
Figure 5.24 comparison between AB21 CORS site and HTDP deviations along z-axis during year 2014 5.6 Revised Position Coordinates of HTDP Software and AB 21 CORS Site (20122016) In this chapter, the given inter-seismic, co-seismic and post-seismic data is used computed by both AB21 CORS site and HTDP software to precisely estimate the crustal
103
displacement associated with 23rd June 2014 Aleutian Islands earthquake. The deviation of AB21 CORS site from its adopted positional coordinates due to North American tectonic plate movement since the time of its installation are also precisely calculated. Now in this section all accurately measured deviations are used to update or revised positional coordinates of AB21 CORS site and HTDP software. As NGS did its last position coordinates revision in 2012, and the Alaskan model of HTDP 3.2.5 version is presented in 2013. However in this paper the revised position coordinates contain all deviations due to co seismic, post seismic activities associated with Aleutian Islands earthquake, and the displacement of the CORS site due tectonic plate movement since 2012 to end dates of 2016. The HTDP software measurements are updated with the help of AB21 CORS site GPS observation data which is post processed by OPUS for higher accuracy. The given below data consist of updated values of HTDP software and its difference with respect to assigned values. Similarly the differences in GPS post processed measurements of AB21 CORS site from adopted NAD_83 position coordinates are due to seismic activities, precisely recorded by the site. The AB21 CORS data is used to update HTDP software position coordinates for the rigid tectonic plate grid model of Aleutian Islands Alaska. 5.6.1 Updated x-axis position coordinates The given below data consist of updated x-axis position coordinate measurements of HTDP software and AB21 CORS site with their differences from assigned values. These xaxis position coordinate measurements contain all deviations due to seismic activities occurred from start of the year 2012 to end of 2016. The measurement differences between updated and assigned position coordinates are also given for both AB21 CORS site and HTDP software. Table.5.10 Updated HTDP software measurements and AB21 CORS site data of x-axis position coordinate
Year (Days)
HTDP Updated x-axis Coordinate (m)
CORS recorded xaxis Coordinate (m)
-3940202.661
HTDP measurement Difference (x) cm 0
-3940202.662
CORS measurement Difference (x)cm 0.1
2012 15
-3940202.661
0
-3940202.661
0
30
-3940202.661
0
-3940202.662
0.1
104
45
-3940202.661
0
-3940202.662
0.1
60
-3940202.661
0
-3940202.661
0
75
-3940202.661
0
-3940202.660
-0.1
90
-3940202.661
0
-3940202.661
0
105
-3940202.661
0
-3940202.661
0
120
-3940202.661
0
-3940202.661
0
135
-3940202.661
0
-3940202.661
0
150
-3940202.661
0
-3940202.661
0
165
-3940202.661
0
-3940202.661
0
180
-3940202.661
0
-3940202.661
0
195
-3940202.661
0
-3940202.661
0
210
-3940202.660
-0.1
-3940202.659
-0.2
225
-3940202.660
-0.1
-3940202.659
-0.2
240
-3940202.660
-0.1
-3940202.661
0
255
-3940202.660
-0.1
-3940202.659
-0.2
270
-3940202.660
-0.1
-3940202.658
-0.3
285
-3940202.660
-0.1
-3940202.659
-0.2
300
-3940202.660
-0.1
-3940202.660
-0.1
315
-3940202.660
-0.1
-3940202.660
-0.1
330
-3940202.660
-0.1
-3940202.660
-0.1
345
-3940202.660
-0.1
-3940202.659
-0.2
360
-3940202.660
-0.1
-3940202.659
-0.2
2013
-3940202.660
-0.1
-3940202.661
0
15
-3940202.660
-0.1
-3940202.661
0
30
-3940202.660
-0.1
-3940202.661
0
45
-3940202.660
-0.1
-3940202.661
0
60
-3940202.660
-0.1
-3940202.659
-0.2
75
-3940202.660
-0.1
-3940202.660
-0.1
90
-3940202.660
-0.1
-3940202.658
-0.3
105
-3940202.660
-0.1
-3940202.660
-0.1
120
-3940202.660
-0.1
-3940202.660
-0.1
135
-3940202.660
-0.1
-3940202.661
0
105
150
-3940202.660
-0.1
-3940202.661
0
165
-3940202.660
-0.1
-3940202.660
-0.1
180
-3940202.659
-0.2
-3940202.659
-0.2
195
-3940202.659
-0.2
-3940202.660
-0.1
210
-3940202.659
-0.2
-3940202.659
-0.2
225
-3940202.659
-0.2
-3940202.659
-0.2
240
-3940202.659
-0.2
-3940202.661
0
255
-3940202.659
-0.2
-3940202.659
-0.2
270
-3940202.659
-0.2
-3940202.660
-0.1
285
-3940202.659
-0.2
-3940202.659
-0.2
300
-3940202.659
-0.2
-3940202.659
-0.2
315
-3940202.659
-0.2
-3940202.659
-0.2
330
-3940202.659
-0.2
-3940202.659
-0.2
345
-3940202.659
-0.2
-3940202.659
-0.2
360
-3940202.659
-0.2
-3940202.659
-0.2
2014
-3940202.659
-0.2
-3940202.659
-0.2
15
-3940202.659
-0.2
-3940202.660
-0.1
30
-3940202.659
-0.2
-3940202.660
-0.1
45
-3940202.659
-0.2
-3940202.659
-0.2
60
-3940202.659
-0.2
-3940202.659
-0.2
75
-3940202.659
-0.2
-3940202.660
-0.1
90
-3940202.659
-0.2
-3940202.659
-0.2
105
-3940202.659
-0.2
-3940202.659
-0.2
120
-3940202.659
-0.2
-3940202.659
-0.2
135
-3940202.659
-0.2
-3940202.659
-0.2
150
-3940202.659
-0.2
-3940202.659
-0.2
165
-3940202.659
-0.2
-3940202.659
-0.2
180
-3940202.619
-4.2
-3940202.618
-4.3
195
-3940202.619
-4.2
-3940202.619
-4.3
210
-3940202.619
-4.2
-3940202.619
-4.2
225
-3940202.619
-4.2
-3940202.619
-4.2
240
-3940202.619
-4.2
-3940202.622
-3.9
106
255
-3940202.619
-4.2
-3940202.620
-4.1
270
-3940202.619
-4.2
-3940202.620
-4.1
285
-3940202.618
-4.3
-3940202.620
-4.1
300
-3940202.618
-4.3
-3940202.620
-4.1
315
-3940202.618
-4.3
-3940202.620
-4.1
330
-3940202.618
-4.3
-3940202.620
-4.1
345
-3940202.618
-4.3
-3940202.620
-4.1
360
-3940202.618
-4.3
-3940202.620
-4.1
2015
-3940202.617
-4.4
-3940202.618
-4.3
15
-3940202.617
-4.4
-3940202.618
-4.3
30
-3940202.617
-4.4
-3940202.618
-4.3
45
-3940202.617
-4.4
-3940202.618
-4.3
60
-3940202.617
-4.4
-3940202.618
-4.3
75
-3940202.617
-4.4
-3940202.618
-4.3
90
-3940202.617
-4.4
-3940202.618
-4.3
105
-3940202.617
-4.4
-3940202.618
-4.3
120
-3940202.617
-4.4
-3940202.617
-4.4
135
-3940202.617
-4.4
-3940202.617
-4.4
150
-3940202.617
-4.4
-3940202.617
-4.4
165
-3940202.617
-4.4
-3940202.617
-4.4
180
-3940202.617
-4.4
-3940202.617
-4.4
195
-3940202.617
-4.4
-3940202.617
-4.4
210
-3940202.617
-4.4
-3940202.616
-4.5
225
-3940202.617
-4.4
-3940202.616
-4.5
240
-3940202.617
-4.4
-3940202.616
-4.5
255
-3940202.616
-4.5
-3940202.616
-4.5
270
-3940202.616
-4.5
-3940202.616
-4.5
285
-3940202.616
-4.5
-3940202.616
-4.5
300
-3940202.616
-4.5
-3940202.616
-4.5
315
-3940202.616
-4.5
-3940202.616
-4.5
330
-3940202.616
-4.5
-3940202.616
-4.5
345
-3940202.616
-4.5
-3940202.616
-4.5
107
360
-3940202.616
-4.5
-3940202.615
-4.6
2016
-3940202.616
-4.5
-3940202.616
-4.5
15
-3940202.616
-4.5
-3940202.617
-4.4
30
-3940202.616
-4.5
-3940202.617
-4.4
45
-3940202.616
-4.5
-3940202.616
-4.5
60
-3940202.616
-4.5
-3940202.616
-4.5
75
-3940202.616
-4.5
-3940202.616
-4.5
90
-3940202.616
-4.5
-3940202.616
-4.5
105
-3940202.616
-4.5
-3940202.616
-4.5
120
-3940202.616
-4.5
-3940202.616
-4.5
135
-3940202.616
-4.5
-3940202.616
-4.5
150
-3940202.616
-4.5
-3940202.616
-4.5
165
-3940202.616
-4.5
-3940202.616
-4.5
180
-3940202.616
-4.5
-3940202.616
-4.5
195
-3940202.616
-4.5
-3940202.616
-4.5
210
-3940202.616
-4.5
-3940202.626
-3.5
225
-3940202.616
-4.5
-3940202.616
-4.5
240
-3940202.616
-4.5
-3940202.616
-4.5
255
-3940202.615
-4.6
-3940202.616
-4.5
270
-3940202.615
-4.6
-3940202.615
-4.6
285
-3940202.615
-4.6
-3940202.615
-4.6
300
-3940202.615
-4.6
-3940202.614
-4.7
315
-3940202.615
-4.6
-3940202.614
-4.7
330
-3940202.615
-4.6
-3940202.614
-4.7
345
-3940202.615
-4.6
-3940202.615
-4.6
360
-3940202.615
-4.6
-3940202.614
-4.7
The figure. 5.25 show the differences between updated HTDP software measurements with respect to the computations of recent HTDP 3.2.5 version along x-axis.
108
HTDP updated Deviation along x-axis
0 -1
2012 60 120 180 240 300 360 45 105 165 225 285 345 30 90 150 210 270 330 15 75 135 195 255 315 2016 60 120 180 240 300 360
Displacement (cm)
1
-2 -3 -4 -5
Years 2012 - 2016 Figure 5.25 updated deviations of HTDP along x-axis (2012-2016) The Figure.5.26 shows the deviation of AB21 CORS site from their assigned NAD_83 (EPOCH 2010) position coordinates along x-axis.
AB21 CORS site Deviation along x-axis
0 -1
2012 60 120 180 240 300 360 45 105 165 225 285 345 30 90 150 210 270 330 15 75 135 195 255 315 2016 60 120 180 240 300 360
Displacement (cm)
1
-2 -3 -4 -5
Years 2012 - 2016 Figure .5.26 AB21 CORS site deviations along x-axis (2012-2016)
The Figure.5.27 depicts that the updated HTDP software x-axis position coordinates are in good agreement with post processed GPS data recorded by Adak AB21 CORS site. The plot represents that there are still some differences between the measurements. It is due to some recorded seismic activities by the CORS site. It is clear from the graphical presentation that a possible data glitch happened on day 210 of year 2016. This single anomaly is not affecting the overall behaviour of the data and can be neglected. 109
1
Comparison of measurements along x-axis 2012 60 120 180 240 300 360 45 105 165 225 285 345 30 90 150 210 270 330 15 75 135 195 255 315 2016 60 120 180 240 300 360
Displacements (cm)
0 -1 -2 -3 -4
Years 2012 - 2016
-5
Figure.5.27 updated HTDP software measurements with AB21 CORS site deviations along x-axis 5.6.2 Updated y-axis position coordinate The updated measurements of HTDP software along y-axis with their differences from recent 3.2.5 version are given in the below table. These HTDP software measurements are revised with the help of AB21 CORS site GPS observations, which are post processed by Online Position User Service. The differences between assigned and post processed measurements are due to seismic activities precisely recorded by the CORS site. Table.5.11 Updated HTDP software measurements and AB21 CORS site data of y-axis position coordinate
Year (Days)
HTDP Updated yaxis Coordinate (m)
CORS recoded yaxis Coordinate (m)
-229769.095
HTDP measurement Difference (y) cm 0
-229769.094
CORS measurement Difference (y)cm -0.1
2012 15
-229769.095
0
-229769.094
-0.1
30
-229769.095
0
-229769.095
0
45
-229769.095
0
-229769.095
0
60
-229769.095
0
-229769.095
0
75
-229769.095
0
-229769.095
0
90
-229769.095
0
-229769.095
0
110
105
-229769.095
0
-229769.095
0
120
-229769.095
0
-229769.095
0
135
-229769.095
0
-229769.095
0
150
-229769.095
0
-229769.096
0.1
165
-229769.095
0
-229769.096
0.1
180
-229769.095
0
-229769.096
0.1
195
-229769.095
0
-229769.094
-0.1
210
-229769.096
0.1
-229769.094
-0.1
225
-229769.096
0.1
-229769.095
0
240
-229769.097
0.2
-229769.095
0
255
-229769.097
0.2
-229769.097
0.2
270
-229769.097
0.2
-229769.097
0.2
285
-229769.097
0.2
-229769.097
0.2
300
-229769.097
0.2
-229769.097
0.2
315
-229769.097
0.2
-229769.097
0.2
330
-229769.097
0.2
-229769.096
0.1
345
-229769.098
0.3
-229769.096
0.1
360
-229769.098
0.3
-229769.096
0.1
2013
-229769.098
0.3
-229769.098
0.3
15
-229769.098
0.3
-229769.098
0.3
30
-229769.098
0.3
-229769.098
0.3
45
-229769.098
0.3
-229769.098
0.3
60
-229769.098
0.3
-229769.098
0.3
75
-229769.098
0.3
-229769.098
0.3
90
-229769.098
0.3
-229769.097
0.2
105
-229769.098
0.3
-229769.097
0.2
120
-229769.098
0.3
-229769.098
0.3
135
-229769.098
0.3
-229769.098
0.3
150
-229769.099
0.4
-229769.098
0.3
165
-229769.099
0.4
-229769.099
0.4
180
-229769.099
0.4
-229769.099
0.4
195
-229769.099
0.4
-229769.099
0.4
111
210
-229769.100
0.5
-229769.099
0.4
225
-229769.100
0.5
-229769.100
0.5
240
-229769.100
0.5
-229769.101
0.5
255
-229769.100
0.5
-229769.102
0.5
270
-229769.100
0.5
-229769.103
0.5
285
-229769.100
0.5
-229769.104
0.5
300
-229769.101
0.6
-229769.105
0.5
315
-229769.101
0.6
-229769.101
0.6
330
-229769.101
0.6
-229769.102
0.7
345
-229769.101
0.6
-229769.102
0.7
360
-229769.102
0.7
-229769.102
0.7
2014
-229769.102
0.7
-229769.102
0.7
15
-229769.102
0.7
-229769.101
0.6
30
-229769.102
0.7
-229769.102
0.7
45
-229769.102
0.7
-229769.102
0.7
60
-229769.102
0.7
-229769.102
0.7
75
-229769.102
0.7
-229769.102
0.7
90
-229769.102
0.7
-229769.102
0.7
105
-229769.103
0.8
-229769.102
0.7
120
-229769.103
0.8
-229769.103
0.8
135
-229769.103
0.8
-229769.103
0.8
150
-229769.103
0.8
-229769.103
0.8
165
-229769.103
0.8
-229769.103
0.8
180
-229769.066
-2.9
-229769.063
-3.2
195
-229769.066
-2.9
-229769.064
-3.1
210
-229769.066
-2.9
-229769.063
-3.2
225
-229769.066
-2.9
-229769.064
-3.1
240
-229769.066
-2.9
-229769.064
-3.1
255
-229769.066
-2.9
-229769.065
-3
270
-229769.066
-2.9
-229769.065
-3
285
-229769.067
-2.8
-229769.065
-3
300
-229769.067
-2.8
-229769.067
-2.8
112
315
-229769.067
-2.8
-229769.067
-2.8
330
-229769.067
-2.8
-229769.067
-2.8
345
-229769.067
-2.8
-229769.068
-2.7
360
-229769.067
-2.8
-229769.068
-2.7
2015
-229769.068
-2.7
-229769.068
-2.7
15
-229769.068
-2.7
-229769.068
-2.7
30
-229769.068
-2.7
-229769.068
-2.7
45
-229769.068
-2.7
-229769.068
-2.7
60
-229769.068
-2.7
-229769.068
-2.7
75
-229769.068
-2.7
-229769.068
-2.7
90
-229769.069
-2.6
-229769.068
-2.7
105
-229769.069
-2.6
-229769.068
-2.7
120
-229769.069
-2.6
-229769.069
-2.6
135
-229769.069
-2.6
-229769.070
-2.5
150
-229769.069
-2.6
-229769.070
-2.5
165
-229769.069
-2.6
-229769.070
-2.5
180
-229769.069
-2.6
-229769.070
-2.5
195
-229769.069
-2.6
-229769.070
-2.5
210
-229769.069
-2.6
-229769.070
-2.5
225
-229769.070
-2.5
-229769.072
-2.3
240
-229769.070
-2.5
-229769.072
-2.3
255
-229769.070
-2.5
-229769.072
-2.3
270
-229769.070
-2.5
-229769.072
-2.3
285
-229769.070
-2.5
-229769.072
-2.3
300
-229769.071
-2.4
-229769.072
-2.3
315
-229769.071
-2.4
-229769.072
-2.3
330
-229769.071
-2.4
-229769.072
-2.3
345
-229769.071
-2.4
-229769.071
-2.4
360
-229769.072
-2.3
-229769.071
-2.4
2016
-229769.072
-2.3
-229769.071
-2.4
15
-229769.072
-2.3
-229769.072
-2.3
30
-229769.072
-2.3
-229769.072
-2.3
113
45
-229769.072
-2.3
-229769.072
-2.3
60
-229769.072
-2.3
-229769.072
-2.3
75
-229769.072
-2.3
-229769.073
-2.2
90
-229769.072
-2.3
-229769.073
-2.2
105
-229769.072
-2.3
-229769.073
-2.2
120
-229769.072
-2.3
-229769.073
-2.2
135
-229769.073
-2.2
-229769.073
-2.2
150
-229769.073
-2.2
-229769.074
-2.1
165
-229769.073
-2.2
-229769.074
-2.1
180
-229769.073
-2.2
-229769.074
-2.1
195
-229769.073
-2.2
-229769.074
-2.1
210
-229769.073
-2.2
-229769.081
-1.4
225
-229769.073
-2.2
-229769.075
-2
240
-229769.073
-2.2
-229769.075
-2
255
-229769.073
-2.2
-229769.075
-2
270
-229769.074
-2.1
-229769.075
-2
285
-229769.074
-2.1
-229769.075
-2
300
-229769.074
-2.1
-229769.075
-2
315
-229769.074
-2.1
-229769.074
-2.1
330
-229769.074
-2.1
-229769.074
-2.1
345
-229769.075
-2
-229769.074
-2.1
360
-229769.075
-2
-229769.074
-2.1
The Figure.5.28 represents the differences of updated values of HTDP software from computed measurements of the latest HTDP software 3.2.5 version along y-axis. These revised measurements contain displacement due to 23rd June 2014 earthquake and the deviations due post seismic activities and tectonic plate movement.
114
HTDP updated Deviations along y-axis 1.5
0.5 0 -0.5
2012 75 150 225 300 2013 75 150 225 300 2014 75 150 225 300 2015 75 150 225 300 2016 75 150 225 300
Displacement (cm)
1
-1 -1.5 -2 -2.5 -3 -3.5
Years 2012 - 2016 Figure 5.28 updated deviations of HTDP along y-axis (2012-2016)
The Figure.5.29 clearly plots all deviations of AB21 CORS site associated with 23rd June 2014 earthquake and displacement due to North American tectonic plate movement since the year of 2012.
AB21 CORS site deviation along y-axis
1
300
225
150
75
2016
300
225
75
150
2015
300
225
150
75
2014
300
225
150
75
300
225
150
2013
-1
75
0 2012
Displacement (cm)
2
-2 -3 -4
Years 2012 - 2016 Figure 5.29 AB21 CORS site deviations along y-axis (2012-2016)
The Figure.5.30 shows that the updated HTDP software y-axis position coordinates agree well with post processed GPS data recorded by Adak AB21 CORS site. The plot represents that there are some dissimilarities between the measurements of HTDP and CORS site. It is 115
due to the precisely recorded seismic activities by the AB21 CORS site. The graphical presentation depicts a probable data variation occurred on day 210 of year 2016. This single deviation does not affect the overall behaviour of the data and can be neglected.
2
Comparison of measurements along y-axis 0 -1
2012 60 120 180 240 300 360 45 105 165 225 285 345 30 90 150 210 270 330 15 75 135 195 255 315 2016 60 120 180 240 300 360
Displacement (cm)
1
-2 -3 -4
Years 2012 - 2016
Figure.5.30 updated HTDP software measurements with AB21 CORS site deviations along y-axis 5.6.3 Updated z-axis position coordinates The below table has data of HTDP software measurements modified by using AB21 CORS GPS observation data. These updated measurements along z-axis include all deviations due to seismic activities during the time span of 2012 to 2016. Table.5.12 Updated HTDP software measurements and AB21 CORS site data of z-axis position coordinate HTDP Updated z-
HTDP
CORS recorded z-
CORS
axis Coordinate
measurement
axis Coordinate
measurement
(m)
Difference (z)cm
(m)
Difference (Z)cm
2012
4993529.398
0
4993529.397
-0.1
15
4993529.398
0
4993529.396
-0.2
30
4993529.398
0
4993529.398
0
45
4993529.398
0
4993529.398
0
Year (Days)
116
60
4993529.398
0
4993529.398
0
75
4993529.398
0
4993529.399
0.1
90
4993529.398
0
4993529.399
0.1
105
4993529.398
0
4993529.398
0
120
4993529.398
0
4993529.398
0
135
4993529.398
0
4993529.398
0
150
4993529.397
-0.1
4993529.398
0
165
4993529.397
-0.1
4993529.397
-0.1
180
4993529.397
-0.1
4993529.397
-0.1
195
4993529.397
-0.1
4993529.396
-0.2
210
4993529.397
-0.1
4993529.396
-0.2
225
4993529.397
-0.1
4993529.396
-0.2
240
4993529.397
-0.1
4993529.397
-0.1
255
4993529.397
-0.1
4993529.397
-0.1
270
4993529.397
-0.1
4993529.397
-0.1
285
4993529.397
-0.1
4993529.397
-0.1
300
4993529.397
-0.1
4993529.396
-0.2
315
4993529.397
-0.1
4993529.396
-0.2
330
4993529.396
-0.2
4993529.396
-0.2
345
4993529.396
-0.2
4993529.396
-0.2
360
4993529.396
-0.2
4993529.395
-0.3
2013
4993529.396
-0.2
4993529.395
-0.3
15
4993529.396
-0.2
4993529.395
-0.3
30
4993529.396
-0.2
4993529.395
-0.3
45
4993529.396
-0.2
4993529.396
-0.2
60
4993529.396
-0.2
4993529.396
-0.2
75
4993529.396
-0.2
4993529.396
-0.2
90
4993529.396
-0.2
4993529.396
-0.2
105
4993529.396
-0.2
4993529.396
-0.2
120
4993529.395
-0.3
4993529.395
-0.3
135
4993529.395
-0.3
4993529.395
-0.3
150
4993529.395
-0.3
4993529.395
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Figure.5.31 plots the differences of updated HTDP software measurements with respect to latest model computations along z-axis. These updated values include all deviations due to seismic activities.
HTDP updated Deviations along z-axis
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Figure.5.32 depicts the differences of post processed GPS observations of AB21 CORS site with respect to assigned values.
AB21 CORS site Deviation along z-axis
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Figure.5.33 shows that HTDP software updated measurements and AB21 CORS site observations are in good agreement with each other. 2.5
Comparison of measurements along z-axis 1.5 1 0.5 0 -0.5 -1
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Figure 5.33 updated HTDP software measurements with AB21 CORS site deviations along zaxis
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06 6.1
CONCLUSION AND RECOMMENDATIONS FOR FUTURE WORK Conclusions
Based on the assessments explained on the previous chapter, the following sections summarises the conclusions that can be drawn. 6.1.1 Precise assessment of Aleutian Islands earthquake
The 23rd June 2014 Aleutian Islands earthquake is recorded by AB21 CORS site. The 24hr observation data is post processed and plotted with the help of RTKLIB by configuring RTKPOST. The satellite navigation file, satellite ephemeris file and satellite clock correction file are used for precise measurement. The position file is used to plot variations in AB21 CORS site position coordinates during the earthquake. The plots clearly depict the position deviations and velocities of AB21 CORS site during as well as before and after the earthquake.
This earthquake is also precisely measured by ANSS IU ADK seismic station. The IU ADK Accelerometer recorded the Aleutian Islands earthquake data during the time span of 89 seconds. In this time period the earthquake achieved its maximum magnitude. During this time period it recorded 200 measurements in each second. The computer processed data consist of displacements and velocities along 360 degree component, 90 degree component and up component.
As the earthquake forces changes so rapidly during an earthquake, they must be measured many times each second (as many as 200). These assessments concluded that the IU ADK accelerometer recorded the earthquake data with 200 sps, however the sample rate of AB21 CORS site is 15sec. The CORS site doesn‘t measure changes that rapid, but is ideal to get final locations once the earthquake is over.
6.1.2 Rigorous measurement of AB21 CORS site deviation after the earthquake
60 days post seismic data recorded by AB21 CORS site is used to compute the deviation of the site from its assigned position coordinates.
This data is post processed by Online Position User Service (OPUS) to achieve centimetre level accuracy.
The post processed data is plotted and it clearly shows a substantial deviation of AB21 CORS site from its assigned coordinates along three axes.
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6.1.3 Deviation of Adak AB21 site due to North American Plate movement
The Adak AB21 CORS site is also deviated from its published position coordinates along three axes due to North American tectonic plate movement.
This displacement is monitored by using AB21 site GPS observation data from 2006 to till December 2016. This data is post processed by OPUS for precise measurements.
6.1.4 Performance analysis of Horizontal Time Positioning (HTDP) Software
A performance analysis is made for Horizontal Time Dependent Positioning (HTDP) software by comparing its measurements with post processed observations of AB21 CORS site during the year 2014.
The difference between HTDP software measurements and AB21 CORS site observations in three dimensions are used to update Horizontal Time Dependent Positioning software computations
6.1.5 Revision of AB21 CORS site Position Coordinates
The Adak AB21 CORS site data since 2012 to till December 2016 is used to update position coordinates along three axes.
This data is post processed by OPUS and it includes all deviations associated with inter seismic, co seismic, post seismic activities and North American tectonic plate movement.
All accurately measured deviations that are incorporated in the revision of AB21 CORS site position coordinates and HTDP software measurements are plotted. The graphs depict that revised position coordinates of AB21 CORS site and HTDP software measurements since 2012 to till December 2016 are in good agreement with each other.
6.2
Recommendations For Future Work
The following are the recommendations for further research into this area
The current NAD83 CORS position coordinates were found by reprocessing all NGS CORS data recorded from January 1994 to April 2011 in the NGS initial Multi-year CORS Solution (MYCS1) project. The assigned CORS position coordinates were published by National Geodetic Survey in September, 2011, and represent a new realisation known as NAD83 (2011), Epoch 2010.00. There is need to revise all NGS 123
CORS sites position coordinates, and to develop a new project of Multi-year CORS Solution since 2012 to till 2017 which comprises a new realisation of NAD 83. This new realisation should include all CORS site deviation due to co seismic, post seismic and interseismic activities associated with 23rd June 2014 Aleutian Islands earthquake in Alaska and especially the CORS sites situated on tectonically active areas such as western United States, significantly deviated from their assigned NAD83 (2011) position coordinates due to substantial tectonic plate displacement per year. In this paper the only AB21 CORS site deviation due to Aleutian Islands earthquake is included, however this earthquake also deviated many other CORS sites like AC66, AC60 and AB01 from their assigned position coordinates. The position coordinates of these mentioned CORS sites should also revise.
The most recent modification of Horizontal Time Dependent Positioning software version 3.2.5 has been done on August, 30 2015. It only modifies corrections for minor rounding error inconsistencies. The last earthquake dislocation model incorporated into Horizontal Time Dependent Positioning software was 3rd November 2002 Denali earthquake. This model was developed in 2013 by Dr. Jeffery of the University of Alaska. There should be a dislocation model for 23rd June 2014 Aleutian Islands earthquake as this earthquake displaced many CORS sites from their assigned coordinates and caused significant crustal deformation in the regions of Aleutian Islands Alaska.
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