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Table of Contents LIST OF FIGURES…………………………………………. LIST OF TABLES…………………………………………… LIST OF ABBREVIATIONS……………………………….. DEDICATIONS……………………………………………... ACKNOWLEDGMENTS…………………………………... AIM AND OBJECTIVES…………………………………… ABSTRACT……………………………………………………. 1. GEOGRAPHY AND METEROLOGY OF STUDY AREA…………………………………………………………… 2. SATELLITE INSTRUMENTATION, DATA & METHDOLOGY ………………………………………………. 2.1 AIRS monthly level 3 products…………. 3. REMOTE SENSING OF THE ATMOSPHERE…………. 3.1 Advantages of atmospheric remote sensing…………………………………………………………... 3.2 Limitations of atmospheric remote sensing…………………………………………………………... 4. RADIOWAVE PROPAGATION AND ATMOSPHERIC EFFECTS……………………………………………………….. 4.1 Anomalous propagation………………….. 4.1.1 Sub refraction………………… 4.1.2 Super refraction……………….. 4.1.3 Ducting………………………. 5. ATMOSPHERIC DUCTS……………………………….. 5.1 Mathematical form of radio refractive index 5.1.1 Conditions for the formula of radio refractivity………………………………………………… 5.2 Modified Refractivity…………………..… 5.3 Types of Modified Refractivity ………….. 5.4 Duct Strength And Duct Thicknes……. 6. STABLE AND UNSTABLE ATMOSPHERIC CONDITIONS………………………………………………….. 6.1 Adiabatic process…………………………. 6.2 Dry Adiabatic Rate……………………….. ϭ

3 5 6 7 8 9 10 11 13 14 15 15 15 17 18 18 19 19 21 24 25 26 26 28 29 29 29

6.3 Moist Adiabatic Rate……………………… 6.4 Environmental Lapse Rate………………… 6.5 Absolute Stable conditions………………... 6.6 Unstable Atmospheric Conditions………… 6.7 Conditional Unstable Environmental……... 7. FACTORS AFFECTING THE RADIO REFRACTIVITY 7.1 Geopotential Height ……………..………... 7.1.1 Definition………………….. 7.1.2 Mathematical Formula…….. 7.1.3 Geopotential Height vs Geometric Height………………………………………………. 7.1.4 Conversion of Geometric Height from Geopotential Height………………………………. 7.1.5 Formula for the acceleration due to gravity at given latitude…………………………………. 7.1.6 Formula for the effective Earth radius at given latitude……………………………………. 7.2 Humidity………………………………….. 7.2.1 Absolute Humidity…………. 7.2.2 Specific humidity & mixing ratio……………………………………………………………… 7.2.3 Vapor Pressure………….… 7.2.4 Saturation vapor pressure…... 7.2.5 Relative Humidity…………. 7.2.6 Temperature & relative humidity…………………………………………………………. 7.3 TEMPERATURE…………………….…….. 7.3.1 Standard Temperauter variations with altitude………………………………………….. 8. RESULTS AND DISCUSSION………………………….. 8.1 Duct Seasons………………………………. 8.1.1 Winter Season………………. 8.1.2 Spring Season……………….. 8.1.3 Summer Season……………... 8.1.4 Autumn Season……………… 9. CONCLUSIONS AND RECOMMENDATIONS ……. REFERENCES…………………………………….……... Ϯ

29 29 29 29 29 30 30 30 30 30 31 31 31 31 32 32 32 32 33 33 34 34 37 37 37 38 39 40 46 47

LIST OF FIGURES

Figure 1.

Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12.

Figure 13.

Figure 14.

Geographical map of Pakistan showing its neighboring countries of Afghanistan, Turkmenistan, Uzbekistan, Tajikistan, India, Iran, and People’s Republic of China……………………………….... Remote sensing of the atmosphere………………. Various forms of atmospheric refraction…………… Basic types of atmospheric ducts (Surface and Elevated Ducts)……………………………………. Concept of radio refraction with types of ducts… Anomalous propagation: ducting…………………… Refractive gradient with different form of refractions.. Different types of modified refractivity profiles with geometric height…………………………… Relationship between daily relative humidity and temperature of the air………………………………. Temperature variation with altitude( in meters). Vertical temperature profile for a windy and a calm summer afternoon………………………………….. Daily variation in the incomming solar radiations,earth out going radiations and air temperature 4-year spatial and temporal mean monthly Geopotential Height (meters) distribution at 700 hPa using AIRS onboard Aqua satellite sensed retrievals in ascending mode over Pakistan during January 2009 to December 2012. White areas in spatial window show no data which was omitted during quality and clouds screening processes……………. 4-year spatial and temporal mean monthly distribution of relativity humidity (%) at 700 hPa using AIRS on board Aqua satellite sensed retrievals in ascending mode over Pakistan during January 2009 to December 2012. White areas in spatial window show no data which was omitted during quality and  clouds screening processes…….. ϯ

11

15 20 21 22 23 26 27 33 35 36 36

41

42

Figure 15.

Figure 16.

4-year spatial and temporal mean monthly distribution of temperature (Kelvin) at 700 hPa using AIRS on board Aqua satellite sensed retrievals in 43 ascending mode over Pakistan during January 2009 to December 2012. White areas in spatial window show no data which was omitted during quality, and clouds screening processes…… Maps showing the spatial and temporal distribution of atmospheric ducts and their averaged strengths (0 to 400 meters and above) for each month over the study 44 region. (Top left for January and Bottom right for December) during January 2009-December 2012…….

ϰ

LIST OF TABLES

Table 1. AIRS instrument properties and specifications. Table 2. Level 3 Standard Product Characteristics Table 3. Conditions and Modified refractivity gradient with resulting phenomena. Table 4. Mean annul global reference atmospheric temperature & pressure Table 5. Summary of ducts for each month during the study period 2009-2012

ϱ

13 14 28 34 39

 

LIST OF ABBREVIATIONS

A ae e es g go g (φ , z )

G H hPa k M dM dz

N

dN dz N dn dh

Ndry Nwet φ ϕ

P T t Re Rmax Rmin z zg

True earth’s radius (average earth’s radius) Effective earth’s radius Water vapor pressure (hPa) Saturated vapor pressure(hPa) Acceleration due to gravity at given latitude Standard gravity at mean sea level Geopotential height Gravity ratio Relative Humidity (% ) Hecto Pascal K factor Modified refractivity (dimensionless) Modified refractivity gradient with height Refractivity Gradient of N with z Index of refraction Rate of change of refraction index with height Dry component of refractivity Wet component of refractivity Latitude Geopotential Height Pressure level(hpa) Temperature (K) Average surface ambient temperature t (oC) for the period of one month or longer Radius of the earth corresponding to given latitude Equatorial radius (6378.137 km) Polar radius (6356.752 km) Geometric Height (m) Geopotential Height (m)

ϲ 

Dedicated to My beloved father Muhammad Saleem & People of Jerusalem

ϳ

ACKNOWLEDGEMENTS

“Praise be to Allah, the cherisher and sustainer of the worlds” (Al-Quran-02:01). Heartiest thanks to Almighty Allah, for bestowing upon me the necessary abilities, motivations and aptitude to conduct this research work. I would then like to show gratitude to my teachers who enabled me to utilize these blessings. I would like to express my sincere gratitude to the research supervisor Mr. Zia-ul-Haq, who guided me in the field of research and his guidance in all aspects of this research made it happen the way it should have been. During this work I have collaborated with many friends for whom I have great regards and I wish to extend my warmest thanks to all of these. My credits go to Bushra Amen M.Phil-Space Science (2013-2014) student of the Department of Space Science for her great contributions in my research. My parents, and all my seniors , take a lot of credit , for sparing me during whole of this work ; they were always there to encourage me and praying for me in my way to success.

Muhammad Usman Saleem

ϴ

AIM AND OBJECTIVES

Aim To investigate tropospheric ducts over Pakistan, India and Afghanistan using satellite derived data.

Objectives

a) To get quality controlled satellite data regarding to geopotential height, temperature and relative humidity over Pakistan, India, Afghanistan & related countries at different pressure levels (100,150,250,300,400,500,600,700,850,900,1000hpa). b) To check the formation of atmospheric ducts at different heights using satellite data. c) To map spatial and temporal distribution of atmospheric ducts. d) To discuss RF propagation through the atmospheric ducts.

ϵ

ABSTRACT

Atmospheric ducts are of great importance to study. These ducts tend to bend radio signals. The applications based on radio signal propagation through atmosphere are subjected to errors and inaccuracies. These applications may include satellite pointing, RADAR detection, location identification, etc. In this study formation of tropospheric ducts and propagation of RF signals through these ducts have been investigated over Pakistan, India, Afghanistan & related countries using satellitesensed data during January 2009 to December 2012. Existence of ducts over large areas in Pakistan is found in different months. We have discussed ducts seasons (spring, summer, autumn, winter) in the study. Large ducts have been found in the month of November followed by March and April. The month of October is found with minimum ducts. Most ducts occur over south eastern parts of Pakistan. This study has also dealt with types of ducts with respect to wave propagation. Mostly super refractive ducts exist in all months over study period. Normal and sub refractive ducts are seen only in the month of October. This study deal also with the permanent ducts exited over study area.

ϭϬ

1.

GEOGRA APHY AND METEOROLOGY Y OF THE STUDY AREA A

Pakistan (22.5-388.5oN, 60.5-78.5oE) is bordered by Affghanistan and Iran in the west, India in the east and the China in the noortheast (figure 1), Arabian Sea is locatted at the south of Pakistan. The countrry has a population of 170.6 million as per 2010 estimates with geographicaal area of 796,095 km2.

Figure1. Geograpphical map of Pakistan showing its neighboring countries of Afghanistan, T Turkmenistan, Uzbekistan, Tajikistan, India, Iran, and People’s Republic of China. Pakistan is divideed into three major geographic areas: thhe northern highlands; the Induss River plain; and the Baluchistan Plateeau. The climate of Pakistan varies from m tropical to temperate with arid conditiions existing in the coastal south region,, in monsoon receives high rainfalls. Thhe forests range ϭϭ

from coniferous alpine and subalpine with trees such as spruce, pine, and deodar cedar in the northern mountains to deciduous trees such as the mulberry-type Shisham in the Sulaiman range in the south region (Ramesha et al, 2011). The major problem is that changing climate of Pakistan also affects the atmosphere, seasons, temperature. Pakistan exited in temperate zone. Climate of Pakistan found from Arctic like conditions on snow clad mountains to Arid and hot in deserts regions. Coastal area is mostly humid. On the whole, the climate is generally dry. The annual average rainfall is about 10 inches. But there are wide variations from year to year and between different regions. For example, the southwestern desert area gets fewer than five inches of rain annually, while eastern Punjab gets more than twenty inches annually and the southern valleys of the Himalayas receive about 70 inches of rain annually in mostly Pakistan. Average temperatures vary from one part of the country to another. The mountain regions in the north and northwest have the coolest weather, with an average temperature of 23.88 0C in the summer and often below in the winter. On the Baluchistan Plateau, temperatures are hot during the summer and cool during the winter. The average temperature is about 26.66 0C in the summer and less than 4.44 0C in the winter. On the Indus Plain, temperatures range from a high of 32.220 to 48.88 0C in the summer to a low of 12.77 0C in the winter. In the deserts, temperatures in the hottest months of May and June can reach 500 C and the coolest temperature averages is 5 0C in January. Dust storms are common in the summer and frost in the winter. The southern coastal region has mild, humid weather most of the year, ranging from 18.88 to 30 0C in the winter. There are four seasons in Pakistan lasting for following durations. A cool, dry winter from November through February; a hot summer season from March through June; and a rainy monsoon season from July through September. The month of October marks the "retreating" monsoon period when the monsoons are over and temperatures gradually begin to cool. The onset and duration of these seasons vary somewhat according to location and from year to year (Mohiuddin, 2007).

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2. SATELLITE INSTRUMENTATION, DATA AND METHOLOGY Atmospheric Infrared Sounder (AIRS) is one of the six instruments onboard the Aqua satellite (launched on May 4, 2002) which has a sun-synchronous orbit. AIRS has a high spectral resolution of 2378 bands in the thermal infrared (3.7 – 15.4 μm ) and 4 bands in the visible (0.4-1.0 μm ).The accuracy of the atmospheric temperature and humidity are 10 C in layer 1 km thick, and 20% in layer 2 km thick in the troposphere. Aqua crosses the equator from South to North at 1:30 PM local time (daytime) in an ascending orbit, and from North to South at 1:30 AM (nighttime) in a descending orbit. Therefore twice daily temperature, humidity profiles are obtained by AIRS. AIRS Level 3 (Version 5) standard daily product (AIRS+AMSU) is available on NASA Goddard Earth Sciences Data and Information Services Center (GES DISC). We have used mean monthly Geopotential Height, Relative Humidity, Surface Temperature, and Temperature at different levels over the study area to investigate the atmospheric ducting phenomena. Pressure levels 100, 150, 200, 300, 400, 500, 600, 700, 850, 925, 1000 hpa has respectively used for the geopotential height, relative humidity, temperature. But for shake we have discussed only ducts at 700hpa level here. See table1 for AIRS specifications. Table No 1: AIRS instrument properties and specifications. (Disc.sci.gsfc.nasa.gov, 2014)

Swath Width Duty Cycle Spatial resolutions

Mass Power Thermal Control

1650Km 1.27Mbps IR:1.35km, VIS/NIR:2.3km Horizontal at Nadir,1km vertical 177 Kg 200W IR detectors: active at 60K passive radiator at 150K & electronics at ambient ϭϯ

Field of view Field of view Temporal resolutions(repeat cycle) No of orbits/day

± 49.5 degree cross track 1. degree circular 1 16days

14.5

2.1 AIRS monthly level 3 products: These products address the interests of those involved in climate trend analysis. That’s why we used this product. Temporal resolution of the AIRS Level 3 Standard product is 8 day (half of the 16 days Aqua orbital’s repeat period) and monthly (calendar) based on their specific needs. We are typically interested in monthly means over long timescales and prefer products with the lowest possible systematic errors (accuracy in temperature 10 C in layers 1 km thick and for humidity 20% in layers 2 km thick in troposphere). AIRS level 3 products are arithmetic means of the daily captured data. There are some gores (cells with no data) exited in the AIRS product due to no coverage of the satellite for that day especially with cloud prominences. See table 2 for the specifications of AIRS level 3 product specifications. Table 2: Level 3 Standard Product Characteristics (Source: Atmospheric Infrared Sounder (AIRS) Instrument Guide — GES DISC) Daily Product “Complex” data , leaves in gores between satellite track(missing)

Area(-900 to 900 N/S) “Simple” data , no “Moderate” data , no gores, complete gores , and some data coverage dropout 8-day Product

10 by 10 spatial 10 by 10 spatial 10 by 10 spatial resolution resolution resolution Monthly ( Calendar) 1 day temporal 8 day temporal resolution resolution based on Aqua 16-day repeat cycle ϭϰ

3. REMOTE SEN NSING OF THE ATMOSPHER RE Remote sensing can be defined as the science of obbservations from a distance (not physicaally in contact with object) see figure 2. 2

Fiigure2. Remote sensing of the atmosphhere 3.1 Advantages of atmospheric remote sensing g: The remote sensiing of atmosphere has advantage of covering c large area. Mostly sensor of rem mote sensing are passive (rely on the natural n illumination source).Thanks to Remote Sensing now we have dayy and night time atmospheric data. Prrediction of weathering phenomena beecome very quickly through remote sensing. Access to everywhere in the gllobe makes it very important for plannning, exploring, modeling atmosphericc parameters. Now we have remote senssing plate forms which are gathering atmospheric a data on visible, infrared and thermal range of spectrum. 3.2 Limitations off atmospheric remote sensing: Remote sensingg science has limitations. Remote sensing has not capability that will provide p all the information’s needed too conduct physical, biological or social science s research. It simply provides som me spatial, spectral and temporal inform mation of value in the manner that we hope h is efficient and economical. Powerful active remote r sensing instruments may becom me un-calibrated remote sensing sensoor data. Therefore we have to take critiical corrections. ϭϱ

Finally, remote sensor data may be expensive to collect and analyze. Interestingly, the greatest expense in a typical remote sensing investigation is for well- trained image analysts, not the remote sensor data (Jenson, 2007).

ϭϲ

4. RADIOWAVE PROPAGATION AND ATMOSPHERIC EFFECTS In free space radio waves travel straight lines but due to present of atmosphere they bend, refracted or reflected. Radio waves bends in atmosphere due to change in refractive index with altitude. Index of refraction is defined as the ratio of the propagation velocity in the free space to that in the medium of interest. The atmosphere is divided among various layers. Normally the index of refraction decreases with altitude, its meaning that the velocity of the propagation increases with altitude, which causing the radio wave to bend downward. In this case, radio horizon (the farthest point where the radio waves travel directly) is extended beyond the optical horizon (horizon visible to our eyes). The index of refraction varies from a value of 1.0 for free space to approximately 1.0003 at the surface of the earth. Since this refractive index varies over a small range it is more convenient to use a scaled unit, N, which is refractivity and defined as N = (n-1) × 106 (1) The advantage of this scale unit (N) is that it always express in millionth. For example, if the n =1.0005, then N has the value of 500. Due to rapid decrease in pressure and humidity with altitude and slow decrease of the temperature with altitude, N normally decrease with altitude and tends to zero. During the atmospheric refraction path clearance calculations, it is convenient to replace the true earth radius, a, with the effective radius, ae and to replace the actual atmosphere with a uniform atmosphere in which radio waves travel in straight lines. The ratio of the effective to true earth radius is known as the k factor.

a k= e a

(2)

With the application of Snell’s law in spherical geometry, it may be shown that as long as the change in the refraction index is linear with altitude, the k factor is given by k=

1 1 + a(

dn ) dh

ϭϳ

(3)

;

dn is the rate of refraction index change with height. dh

It is usually more convenient to consider the gradient of N instead of gradient dn/dh. Making the substitution of

dN dn for and also entering the value of dh dh

6370km for ‘a’ into (3) yields the following k=

157 157 + a (

Where

(4)

dN ) dh

dN is the N gradient per kilometer, under most atmospheric dh

conditions, the gradient of N is negative constant and has a value of approximately dN = -40units dh

Substituting (5) into (4) giving the value of k =

(5) 4 this is generally used in 3

propagation analysis. An index of refraction that uniformly decrease with altitude resulting k =

4 is referred to as Standard Refraction. 3

4.1 Anomalous Propagation: Refractive index varies with height which is significantly different from the average value due to weathering conditions. Atmospheric refractive index and k factor may be negative, zero, and positive. These various conditions are shown in the figure 3.Standard refraction is the average conditions show in the figure 3. Including sub refraction, super refraction and ducting are observed in a small percentage of time and collectively referred to as Anomalous propagation.

4.1.1 Sub refraction (k 2) This phenomenon causes radio waves to refract downward with a curvature greater than normal. The result is an increased flattening of the effective earth. For that case the effective earth radius is infinity, it means that the earth reduces to a plane. From equation (4) it can be seen that an N gradient of -157 units per kilometer gives a k equal to infinity. Under these conditions radio waves are propagated at a fixed height above the earth's surface, creating unusually long propagation distances and the potential for overreach interference with other signals occupying the same frequency allocation. This refractive condition arise when the index of refraction decreases more rapidly than normal with increasing altitude, which is produced by a rise in temperature with altitude, or a decrease in humidity, or both. An increase in temperature with altitude, called a temperature inversion, occurs when the temperature of the earth's surface is significantly less than that of the air, which is most commonly caused by cooling of the earth's surface through radiation on clear nights or by movement of warm dry air over a cooler body of water.

4.1.3 Ducting (k