Research Team: Abolghasem Akbari. Under supervision of: Dr. Faridah Othman.
Prof, Dato Dr. Azizan Abu Samah. Department of Civil Engineering,. University ...
Research Team: Abolghasem Akbari Under supervision of: Dr. Faridah Othman Prof, Dato Dr. Azizan Abu Samah Department of Civil Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia Email:
[email protected]
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Study area .
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
What is DEM? Digital elevation model (DEM): One. of two techniques based on the geographic information system (GIS) used in hydrologic modeling (as an alternative to maps and field surveys) to provide a digital representation of watershed topographical characteristics. ADRIEN, N. G. (2004) Computational Hydraulics and Hydrology: An Illustrated Dictionary. An Illustrated Dictionary. Florida, CRC PRESS
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Related terms and definitions WATERSHED:
A geographic area in which water, sediment or other materials . will drain to a common outlet such as a river, stream, lake or swamp. PFAFFLIN, J. R., ZIEGLER, E. N. & LYNCH, J. M. (2008) The Dictionary of Environmental Science and Engineering. The Dictionary of Environmental Science and Engineering. Second edition ed. New York, Routledge
CATCHMENT:
A drainage basin, or the area drained by a particular river system. Adjacent drainage basins are separated by watersheds. In North America, the term watershed refers to the entire drainage basin, and the height of land between basins referred to as a divide.
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Why it is important
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Why watershed is important
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Where and how we get the DEM Data? Sources: •USGS DEM, NED, DTEMD,ETOPO30, SRTM, ASTER •Interpolated from points and lines •Generated photogrammetrically •LiDAR, ifSAR DEM construction issues •Resolution and extent •Projection (for hydrology equal area) •Source elevation data •Interpolation techniques (IDW, Spline, via TIN) Problem with the contour input
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Ø Digital topo maps According to the index map of the study area (figure-2), nine digital topo sheets at the scale of 1:25,000 (series L8028) and twenty-four digital topo sheets at the scale of 1:10,000 (series L808) were obtained from the Malaysian department of surveying and mapping known as JUPEM. The relief is shown as contour lines with 20 and 5 meters interval respectively and spot heights for some selected points such as hill tops and ridges. The Digital topo sheet is the cartographic production based on aerial photographs. Projection used is the Rectified Skew Orthomorphic (RSO) and Rectified Skew Orthomorphic Grid (meter) (JUPEM, 2009). the reason for the selecting two scales was due to discontinuity of some contour lines at the scale of 1:25000.
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Common approach in development of watershed modeling is the use of digital or analogue topography maps
Paper topo sheet 1:2,5000
Digital Topo sheet 1:25,000
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Source of Digital topo data
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Problem with the digital topo maps q Cost q Unavailable coverage for all countries q covering small area which arise the matching
edge problems q Not updating q Many error and need editing q licensing q Time consuming q Purchasing process q Editing and pre-processing
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
The main objective of this research is to centroid elevation.
Project area: 1275 km2 LiDAR sensor: ALTM 3100EA Average point spacing: 0.7m Vertical Data accuracy: 0.2m RMSE
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
High cost of LiDAR (Light Detection and Ranging)
www.aamhatch.com.au
[email protected] ©AAMHATCH Pty Limited Source: the horizon Issue 38,Quarter 3, 2006
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Digital topo map: several sheet is needed
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Filling the urban area with topo at scale 1:10,000
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Typical errors and problems of digital topo maps. Undefined contour lines Edge matching
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Code consistency Disconnecting contour lines especially in urban area
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
How problems effects the DEM
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Free Nearly Global Hydrological Dataset
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Free Nearly Global Hydrological Data
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
HydroSHEDS (Hydrological data and maps based on SHuttle Elevation Derivatives at multiple Scales)
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
SRTM digital elevation data
ØThe
Shuttle Radar Topography Mission (SRTM) (Zyl, 2001) is a joint project of NASA and the U.S. National Imagery and Mapping Agency (NIMA). SRTM collected data during a shuttle flight in February 11, 2000.
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
q The technical process of acquisition and derivation is described
by Rodriguez et al. (2005). q The NASA released the SRTM dataset for some regions, with 3arc-second resolution for the globe, and 1-arc-second for the United States in 2003. q SRTM elevation data is provided in geographic projection (latitude/longitude) referenced to the WGS84 horizontal datum, and EGM96 (Earth Gravitational Model 1996) vertical datum (Lehner et al., 2008). Resolution Identifier
In sec/min
In degree
In meters/km
1s (USA only)
1 arc-second
0.0002777
~ 30 m at the equator
3s
3 arc-second
0.0008333
~ 90 m at the equator
15s
15 arc-second
0.0041667
~ 500 m at the equator
30s
30 arc-second
0.0083333
~1 km at the equator
5m
5 minute
0.0833333
~10 km at the equator
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
The data cover the entire globe (latitudes 60N – 56S), with downgraded resolution of 3 arc-seconds. The 1-second original data have been made available to the public only for North America.
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
http://srtm.csi.cgiar.org ftp://e0mss21u.ecs.nasa.gov/srtm/ http://gisdata.usgs.net/website/HydroSHEDS/viewer.php Whilst the data coverage is global, some regions are missing data because of a lack of contrast in the radar image, presence of water, or excessive atmospheric interference. These data holes are especially concentrated along rivers, in lakes, and in steep regions (often on hillsides with a similar aspect due to shadowing, particularly in the Himalayas and the Andes, for example). This non-random distribution of holes, ranging from 1 pixel to regions of 500 km2, impedes the potential use of SRTM data, and has been the subject of a number of innovative algorithms for “filling-in” the holes through various spatial analysis techniques ( Reuter et al., 2007). International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
The main objective of this research is to
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Error existing in original SRTM data:
In its original release, SRTM data contains regions of no-data (voids), specifically over large water bodies, such as lakes and rivers, and in areas where radar-specific problems prevented the production of reliable elevation data. These areas include mountainous regions where the radar shadow effect is pronounced, such as the Himalayas and Andes, as well as certain land surfaces, such as bare sand or rock conditions as found in the Sahara Desert. The existence of no-data in the DEM causes significant problems for deriving hydrological products, which require continuous flow surfaces (Lehner et al., 2006)
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
Perhaps the most important message is that SRTM-derived DEMs provide greater accuracy than TOPO DEMs, but do not necessarily contain more detail. Cartography at scales of 1:25,000 and below (i.e., 1:10,000) contains topographic features not captured with the 3-arc second SRTM DEMs. However, if only cartography with scales above 1:25,000 (i.e., 1:50,000 and 1:100,000) is available, it is better to use the SRTM DEMs. This statement holds for use of SRTM DEMs for terrain derivatives (slope, aspect, landscape classifications, etc.) as well as pure elevation. For hydrological modeling, SRTM 3-arc second DEMs perform well, but are on the margin of usability. If good quality cartography of scale 1:25,000 and below is available, better results may be expected through digitizing and interpolating the cartographic data.(Jarvis et al., 2004)
International Workshop on Hydrology Data Management and Modeling in South East Asia 20-24 July 2009
SRTM data are provide in lat/long coordinate system based on the WGS84 datum. In this case data convert to the RSO coordinate system. outSRTM=iff(inSRTM
