onaolapo olayinka

8/14/2019 Onaolapo Olayinka

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STUDY OF THE EFFECT OF ATMOSPHERIC PRESSURE ON RADIO

REFRACTIVITY VARIATION IN TROPICAL REGION USING NIGERIA

AS A CASE STUDY.

BY

ONAOLAPO, OLAYINKA S.

(011911)

BEING A PROJECT REPORT SUBMITTED

TO

THE DEPARTMENT OF ELECTRONIC/ELECTRICAL ENGINEERING

FACULTY OF ENGINEERING AND TECHNOLOGY

LADOKE AKINTOLA UNIVERSITY OF TECHNOLOGY,

OGBOMOSO, OYO STATE, NIGERIA.

IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR

THE AWARD OF BACHELOR OF TECHNOLOGY (B.TECH.HONS) IN

ELECTRONIC/ELECTRICAL ENGINEEERING.

NOVEMBER, 2007.


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CERTIFICATION

I certify that this work was carried out by Onaolapo, Olayinka S. of the

department of Electronic and Electrical Engineering, Faculty of Engineering and

Technology, Ladoke Akintola University of Technology, Ogbomosho.

_______________________ ___________

Mrs O. AGUNLEJIKA Date

(supervisor)

_______________________ ___________

Engr. G.O AJENIKOKO Date

(Head of Department)


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ACKNOWLEDGEMENT

My immense appreciation goes to the almighty God, for sparing my life through

ups and downs and for the successful completion of my project work. I acknowledge his

presence in my life and forever thankful for his guidance towards my success in life.

My profound gratitude goes to my supervisor Mrs. Agunlejika O., for her

encouragement and useful suggestions. I am grateful to all those that have assisted me in

the execution of my project; Shola, Yomi, Femi, Deji, Bukola, Mr Godswill, Mr

Adewale, Aunty Amoke and to my fellow course mate.My deep appreciation goes to my rare gem of inestimable value; Mr and Mrs

Onaolapo- my parents for their support, morally and financially. My love goes to all

members of the family for their immense contribution and I pray that we will always be

bonded in unity.

Onaolapo, Olayinka S.

November, 2007.


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TABLE OF CONTENTS

CONTENT PAGE

Title page i

Certification ii

Dedication iii

Acknowledgement iv

Table of content v-vii

List of Tables viii

List of Figures ix

Abstract x

CHAPTER ONE

Introduction 1

1.1 Preamble 1

1.2 Aims and Objectives 4

1.3 Significance of study 4

1.4 Scope of the project 5

1.5 Methodology 6

CHAPTER TWO

Literature Review 8

2.0 Introduction 8

2.1 Refraction 9

2.1.1 Ducting 11


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2.1.2 Factors responsible for ducting 14

2.1.2.1 Evaporation Ducts 14

2.1.2.2 Temperature Inversion 14

2.1.2.3 Subsidence 15

2.2 Atmospheric Boundary Layer 15

2.3 Measurement of Radio Refractivity 16

2.4 Multipath Propagation 17

2.5 Review of work done on Radio refractivity 19

CHAPTER THREE

METHODOLOGY 21

3.1 Data Collection 21

3.2 Method of Analysis 22

3.3 Sample of Analysed Parameters 23

CHAPTER FOUR

RESULTS AND DISCUSSION 26

4.1 Introduction 26

4.2 Estimating the value of Atmospheric Parameter 26

4.3 Effect of Pressure on Surface Refractivity 30

4.4 Seasonal Variation of Surface Refractivity 30

4.5 Regional Variation of Surface Refractivity 32

CHAPTER FIVE

CONCLUSION AND RECOMMENDATIONS 33

5.1 Suggestion for Future Work 34


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REFERENCE 36

APPENDIX A 37-42

APPENDIX B 43-58

APPENDIX C 59-66

GLOSSARY 67


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LIST OF TABLES

PAGE

TABLE4.1 Table of Refractivity, keeping Temperature, Relative Humidity

constant and varying pressure. 27

TABLE4.2 Table of Refractivity, keeping Temperature, Pressure constant

and varying Relative Humidity.

28

TABLE4.3 Table of Refractivity, keeping Relative Humidity, Pressure constant

and varying Temperature.

29


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LIST OF FIGURES

PAGE

FIGURE 2.1 Four basic category of Refraction. 12


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ABSTRACT

This project work investigated the effect(s) of atmospheric variables on radio

refractivity and its input on radio and radar performance. Atmospheric variables of

pressure, temperature and humidity were obtained from radiosonde stations in three

regions i.e Ikeja, Minna, and Kano.

By using Microsoft Excel software, the statistical analysis of values obtained for

pressure, temperature and relative humidity is carried out. The monthly mean values of

radiosonde data- pressure, temperature and relative humidity- collected from threemeteorological stations in Nigeria were estimated. The surface refractivity was calculated

by using an equation that relates temperature, pressure and water vapour pressure. The

seasonal and regional variation of refractivity and the effect of pressure on these

variations were determined.

It was observed that refractivity is directly proportional to the pressure.

Comparing the value of refractivity at the selected centers it was also observed that

refractivity varies both seasonally and regionally.

This research work can be used as tool in proper planning and design of

telecommunication links.


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CHAPTER ONE

INTRODUCTION

1.1 PREAMBLE

The speed of propagation of an electromagnetic wave may be considered to be

constant and equal to the speed of light in free space, 3 x 10 8 ms-. However, the

troposphere as an inhomogeneous medium with changing refractive index is significantlydifferent from free space; it is sufficiently different to produce observable changes in the

speed and in direction of propagation of radio waves [1] . Therefore, electromagnetic

waves propagating within the troposphere do not travel in straight lines but are generally

refracted.

In a standard atmospheric condition, refractivity decreases with height. There are

two situations, however, that can change this standard condition. The first is an abrupt

decrease of water vapour pressure with height, which occurs mostly in narrow layer over

water surface and results in the so called evaporation duct. The other is an inverse

increase of temperature with height causing surface or elevated duct in various ranges of

heights [3] . Depending on the refractivity profile, various well known and described

effects such as sub-refraction, super-refraction, or ducting can occur causing shortening

or extending radio horizon and possibly resulting in interference effects. When

characterizing the radio propagation environment, it is usual to consider the vertical

refractivity gradient of the air of the first kilometer above ground level to estimate


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propagation effects such as ducting, surface reflection and multi-path on terrestrial line-

of-sight links.

Effects of refraction include the introduction of errors in the radar measurements,

bending of radio waves and others. Some of these effects are as explained below:

(1) Extension of the radio horizon

The quantity of the refractive index n, depends on temperature, pressure and of

water vapour, and decreases with height in the troposphere. Since its height gradient

(dn/dz) is negative, radio waves in the troposphere are bent downwards. The effect of

tropospheric refraction is to extend the distance to the horizon, thus increasing theweather radio coverage. Bending of radio waves in the troposphere is caused by the

variation with altitude of the velocity of propagation [2] .

(2) Angular Error caused by Refraction

Another effect is the introduction of error in the measurement of elevation angle.

Tropospheric refraction is troublesome primarily at low angles of elevation, especially

near the horizon. Refraction causes the radio rays to bend, resulting in an apparent

elevation angle different from the true one. Therefore, it is necessary to make corrections

to the radar data due to atmospheric refraction in order to obtain a better estimate of

elevation angle or range. In general, surface observation of radio refractivity seems to

suffice for overcoming the effects of tropospheric refraction.

(3) Anomalous Propagation of Radio Waves

In the lower troposphere, water vapour differences are most important in

accounting for differences the refractive index, n, but at higher altitudes where water


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vapour pressure are low, changes in the refractive index are mostly a result of changes in

temperature.

The abnormal propagation of electromagnetic waves is called ducting or super-

refraction. A duct is produced when the index of refraction decreases with altitude at

rapid rate. A temperature inversion is very pronounced in order to produce super-

refraction. The duct acts as a guide directing energy to great distance. A super-refracting

duct which lies close to the ground is called a ground - based duct, while one lying above

the surface is called an elevated duct.

There are several meteorological conditions which may lead to the formation of super-refracting ducts, such as:

(i) Nocturnal radiation, which occurs on clear night when the ground is moist, leads to a

temperature inversion at the ground and a sharp decrease in moisture with height. These

conditions frequently produce abnormal propagation of radio waves.

(ii) The movement of warm dry air from land, over cooler bodies of water produces a

temperature inversion. In this way strong ducts and extreme anomalous propagation of

radio waves are produced. In general, low - sited radio transmitters are more susceptible

to super-refraction than are high - sited ones.

The term anomalous propagation includes both super-refraction and sub-refraction. The

Refractive index gradient may bend radar rays upward rather than downward, leading to a

decrease in range as compared with standard conditions. This is called sub-refraction.


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1.2 AIM AND OBJECTIVES

To determine the effect of pressure on the variation of refractivity in tropical region.

To collect data of pressure, relative humidity and temperature from three

meteorological centres Lagos (ikeja) - a coastal area, Minna- a savannah region and

Kano- a sub sahelian region.

To calculate the refractivity from the average values of pressure, relative humidity

and temperature obtained. To carry out the statistical analysis of values gotten above and determine the regional

and seasonal characteristics of radio refractivity.

To determine the effect(s) of pressure on refractivity

1.3 SIGNIFICANCE OF STUDY

As a result of changing refractive index of the medium between the transmitting

and the receiving antenna, microwave signal may be loss. Effects such as signal

variations i.e. slow variations which are due to major changes in refractive index are

weather dependent. They are not strongly dependent on frequency. This study will

provide information that will be of help in the design of communication links. It will also

help in understanding the effect(s) of atmospheric variables on radio refractivity and its

impact on radio and radar performance radio and radar performance.

This work will help in providing reasonable information for design of

communication link in that the result obtained after computing and analyzing the required


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data i.e. pressure, temperature and relative humidity will help determine when ducting,

super-refraction, sub-refraction and multi-path fading will occur. Therefore the result will

aid communication engineer to know the frequency and power at which to transmit

information and also to determine the best region and season that will yield the best result

for location of communication link.

By relating the radiosonde data of temperature, humidity and pressure to

refractivity, it will be seen that variation of temperature, humidity and pressure result to

changes in refractivity. In an atmosphere of constant refractivity, no bending of

electromagnetic wave occurs regardless of the value of refractivity. Therefore the effectsof atmospheric variable on radio performance can be seen as electromagnetic wave bends

with changes in value of atmospheric variable such as temperature, pressure and relative

humidity.

1.4 SCOPE OF THE PROJECT

The radiosonde data of temperature, humidity and air pressure are obtained from

three geographical regions in Nigeria, which are: Lagos (Oshodi) (62"N, 345"E), Minna

(930"N, 615"E) and Kano (122"N, 830"E). The analysis of these data was carried out

for a period of eight years (1998-2005). Although, the initial aim was to get the data for a

period of ten years (1997-2006) which could not be obtained due to logistic problems.

Since Nigeria was used as a case study, the data gotten are only peculiar to that of

a tropical region which means the values gotten will be definitely different from those

gotten from temperate and artic region.


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The values pressure and refractivity obtained are used in analysing the effect of

pressure on the variation of refractivity in tropical region.

1.5 METHODOLOGY

Meteorological factors such as pressure P, temperature T and relative humidity

(Pv) measured directly by means of radiosonde are collected. By using Microsoft Excel

software, the statistical analysis of values obtained for pressure, temperature and relative

humidity is carried out. The sum and mean value of radiosonde data obtained i.e.

pressure, temperature and relative humidity was calculated respectively on monthly basisfor the region of Lagos, Kano and Minna.

The surface refractivity was calculated by using an equation that relates

temperature, pressure and water vapour pressure which will be seen in chapter two. The

graph of refractivity is plotted against each month of the year to determine the variation

of refractivity on each month. The graph of pressure against each month of the year is

also plotted to determine the variation of pressure on each month. By comparing the

refractivity to the pressure for each month of the year, the effect of pressure on

refractivity will be determined. The seasonal variation is determined from the fluctuations

of refractivity with each season of the year. The regional variation will be seen by

comparing and relating the analysis of the three regions. The value of sea level

refractivity No is calculated by:

hbso N N

= exp 1.1

Since for tropical region, the scale height b = 7km (Kolawole & Owolabi, 1982) [4]

Where,


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h = the vertical height in kilometers

N s = the surface refractivity

b = the scale height for the three stations

NO= sea level refractivity

The surface height for the three selected stations are as listed below:

Ikeja = 128.55m

Minna = 259.59m

kano = 475.8m.


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CHAPTER TWO

LITERATURE REVIEW

2.0 INTRODUCTION

All electromagnetic radiation (EM) propagation through the atmosphere is

affected by the atmosphere. EM energy can be reflected, refracted, scattered, and

absorbed by different atmospheric constituents. The extent of these atmospheric effects

depends upon both the frequency and power of the EM source and on the state of the

atmosphere through which the EM energy must propagate.

The refractivity (N) of the neutral atmosphere can be related to pressure and

temperature through the following formula (Bean and Dutton, 1968) [5] :

(2.1)

(2.2)Where n is the refractive index, T is the air temperature (K), P is the atmospheric pressure

(hPa) and P V is the water vapour pressure (hPa).

There are two terms, the 'dry term' which covering dry gases, mainly Nitrogen and

Oxygen and the 'wet term' governed by water vapour. The first part of equation (2.1) is

the dry term and the second part after the addition sign is the wet term.


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Furthermore, Willoughby (1997) expressed equation 2.1 as the dry (N dry) and wet

(N wet) components of refractivity. The first term can be called the N dry which comprises

of pressure and temperature and the second term be called N wet which comprises of water

vapour pressure and square of temperature. He further reiterated that the first term

contributes about 70% to the total value of N and the wet term is responsible for 30%.

Willoughby further reiterated that at low temperature N wet reduces to a very small value

even for saturated air and this makes refractivity N almost independent of relative

humidity. An increase in temperature will force N dry to decrease but, at the same time,

cause a rapid increase in the saturated value N wet-max . At high temperatures Ns wet-max may become greater than N dry so that N will vary with the relative humidity when both

temperature and relative humidity are high; N becomes very sensitive to small changes in

both variables.

2.1 REFRACTION

Refraction is the bending of light rays due to refractive index (density) changes in

the atmosphere. For visible and Infra-red (IR) propagation, refraction can cause image

distortion, image inversion, and path length changes important for laser ranging.

Refractive conditions are characterized by comparison to the refraction expected from a

standard atmosphere. Differences from standard conditions are due to temperature and

water vapour density fluctuations. Large gradients of these parameters near the ocean

surface can seriously affect surface horizontal propagation paths. Propagation over slant

paths is usually not seriously affected by refraction.

The index of refraction of a medium, n is defined by:


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refractivity must also exist. Battan (1973) showed that when the gradient of refractivity

(i.e., dN/dZ) is equal to 157 km -1, a propagating electromagnetic wave will bend with a

curvature exactly equal to that of the Earth. Bending would cause a horizontally

propagating electromagnetic wave to remain constantly parallel to the Earth's surface,

always at the same height. Any value of dN/dZ less than -157 km -1 would cause an

electromagnetic wave to bend with greater curvature than the Earth's surface; therefore, -

157 km -1 is the threshold for "trapping" of an electromagnetic wave.

2.1.1 DUCTING

Trapping, or ducting, occurs when the microwave energy is trapped in layers and

propagates to greater ranges than normal because of the lack of vertical spreading of the

rays. Ducting regions can be elevated or surface based. Electromagnetic wave is affected

by the refractive nature of the atmosphere. Nonstandard refractive conditions lead to

anomalous propagation and can cause microwaves to be refracted less than normal (sub-

refraction), refracted more than normal (super-refraction), or trapped in wave-guide

modes (ducted) as in Fig. 2-1.

Over the oceans, a persistent surface ducting mechanism is the rapid, near-surface

decrease in moisture due to evaporation, which creates evaporation ducts. The relation for

the vertical gradient of refractivity as a function of temperature , pressure , and specific

humidity (q) is given by Equation (2.4).

(2.4)

Where, P is the pressure, q the specific humidity and T is the temperature


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Figure 2.1 Four basic categories of Refraction

It is sometimes convenient to think of the Earth's surface as flat and to represent

the EM wave refraction in this frame of reference. A modified refractivity M has been

developed to take into account the Earth's curvature and to allow for easy identification

of ducting. The relationship of M to N is as follows (Battan, 1973):

M = N + 157Z (Z in km) (2.3)

Where,

Z = height in km

M = modified refractivity

N = refractivity

The radio waves can become trapped between a layer in the troposphere and the

surface or even between layers in the troposphere depending on the refractivity profile.

This is generally called a duct and is a waveguide like mode of propagation. As a result,

energy is constrained into two dimensions as it can spread out horizontally but not

vertically. This means the path loss increases directly with range rather than with range

squared, resulting in much lower path losses and very high signal levels at long ranges.

Ducting is caused by strong low level inversions (temperature increases with height),

ducting can also occur when a strong cap of warm and dry air exists in the lower

troposphere above very moist air. Ducting is more common in the morning hours since

this time of the day experiences the strongest low-level inversions (due to cooling of

earth's surface through long wave radiation emission) but ducting can also occur anytime

a strong cap exists in the lower troposphere.


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When trapped between an elevated layer and the surface in a surface duct,

extended propagation will occur if the reflection from the ground is low loss. The angles

are small and low loss reflections can occur, especially where the roughness of the terrain

is small compared to the wavelength. When trapped between layers within the

troposphere in an elevated duct is formed and the refraction loss depends on the

roughness of the layers. The major cause of ducting is humidity and temperature

inversion.

2.1.2 Factors responsible for ducting

2.1.2.1 Evaporation Ducts

There is usually a region for a few metres above the surface of the sea where the

water vapour pressure is high due to evaporation. This also occurs over large bodies of

water, for example the great lakes [6] . The thickness of the duct varies with temperature of

the location, typically 5m in the North Sea, 10-15m in the Mediterranean and often much

more over warm seas as in the Caribbean and Gulf. Naturally, these ducts have a

significant effect on Shipping and have been extensively researched. It is the reason that

VHF/UHF propagation over sea can extend to great distances causing all sorts of

international frequency co-ordination problems.

2.1.2.2 Temperature Inversions

Usually, temperature falls with height by about 1Kelvin per 100m. On clear nights

the ground cools quickly and this can result in a temperature inversion, where the air

temperature rises with height. If it is dry, the temperature term is dominant and super

refraction and ducting can occur. This is particularly common in desert regions.


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If there is significant water vapour the relative humidity can quickly rise to 100%

and vapour condenses out as fog. This condensation reduces the water vapour density

near the ground leading to cold dry air near the ground, warmer moister air above and

results in sub-refraction. This can lead to multi-path on otherwise apparently perfectly

good line of sight links.

2.1.3.3 Subsidence

This is a mechanism that can lead to elevated ducts and is associated with high

pressure weather systems - anticyclones. Descending cold air forced downwards by the

anticyclone heats up as it is compressed and becomes warmer than the air nearer the

ground leading to an elevated temperature inversion. (Atmospheric pressure always

increases closer to the ground). This all happens around 1-2km above the ground far too

high to cause ducting except for very highly elevated stations as the coupling angle into

the duct is too great for a ground based station. As the anticyclone evolves the air at the

edges subsides and this brings the inversion layer closer to the ground. A similar descending effect happens at night. In general, the inversion layer is lowest close to the

edge of the anticyclone and highest in the middle. Anticyclones and subsequent

inversions often exist over large continents for long periods.

2.2 ATMOSPHERIC BOUNDARY LAYER

Propagating electromagnetic waves, unless in a completely homogeneous

medium, will experience some degree of bending due to changes in the index of

refraction. The Earth's atmosphere is normally a very inhomogeneous fluid. Certain

regions, such as the Atmospheric Boundary Layer (ABL), characteristically have large


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mean gradients in temperature and/or humidity. Rapid vertical changes in both

temperature and humidity create layers that significantly refract propagating

electromagnetic signals.

This phenomenon is readily apparent, for example, in the evaporation duct at the base of

the Marine Atmospheric Boundary Layer (MABL) and in the elevated trapping layer

associated with the inversion layer at the top of the ABL.

The ABL is defined by Stewart (1979) as the portion of the lower atmosphere that

has turbulent flow and is in direct contact with the Earth's surface. The ABL extends

from the surface to a height of a few meters in conditions of strongly stable stratificationand to thousands of meters in highly convective conditions. On the average, the ABL

extends through the lowest 3,300 ft (~1Km) of the atmosphere and contains 10 percent of

the mass of the atmosphere. The boundary layer is very important to the dynamics and

thermodynamics of the atmosphere because it is in this layer that all momentum, water

vapor, and thermal energy exchanges between the atmosphere and the Earth's surface

takes place.

2.3 MEASUREMENT OF RADIO REFRACTIVITY

(a) Direct method : The microwave refractometer is used. It is capable of measuring

rapid fluctuations in refractivity. The refractometer measures the change in the resonant

frequency of a cylindrical cavity with ends open to the atmosphere and compares with the

resonant frequency of a standard cavity sealed from the atmosphere. The refractometer is

usually mounted on an aircraft for obtaining N-height profile; hence it is an expensive

technique [7] .


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(b) Indirect method : refractivity can be computed from measured pressure, temperature

and water vapour pressure. The various methods of indirect method are listed below:

(i) Tethered balloon system can be used for height profile in the first km of the

troposphere. It has poor time resolution because each profile can take up to one hour.

(ii) Meteorological sensors can be installed at intervals on a, tower for measurement of

the three parameters pressure, temperature and relative humidity. It is only applicable to

the lowest 200 m part of the atmosphere.

(iii) Upper air meteorological data measurements using radiosondes are carried out at

some hundreds of stations all over the world, with launches at 0000 hrs GMT and 1200hrs GMT. This system provides a large volume of data for statistical analysis, but the

spatial and temporal resolutions of the data are poor for radio communication

applications.

(c) Sodar : This is an acoustic sounding system, which is very useful for studying

temperature inversions which cause radio ducts.

2.4 Multipath Propagation

Multipath fading occurs primarily at night, but can occur during the day or

whenever the lower atmosphere is thoroughly mixed by rising convection current and

winds. On clear night with little or no wind, sizable irregularities or layer can collect at

random elevations and these irregularities in refraction result in multipath transmission

on path lengths of the order of million wavelength or longer. It tends to build up during

the night with a peak in the morning hours and then disappear as the layer is broken by

convection caused by heat of the early morning sun [7] .


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The presence of distinct propagation paths give rise to variations in the received

signal (amplitude and phase) in accordance with the mutual relationship between the

amplitudes and phases of the separate signal contributions. The main effect is the

generation of fades, which includes variations of the amplitude, the phase and the

polarization of the received signal. multipath fading (MPF) is a principal cause of outage

in medium and high capacity microwave digital r adio systems. The diurnal and seasonal

variations of multipath propagation are closely related to the occurrence of the

meteorological conditions causing multipath propagation.

In cases, where strong surface reflection has been prevented, the fading can be dividedinto 3 types:

(i) Rapid Scintillation - these are usually small amplitude fluctuations, which may not be

significant and they are more noticeable at frequencies above 10 GHz.

(ii) Slow non-selective fading due to single path propagation effects. It occurs during

stratified atmospheric conditions and is less severe than multipath fading.

(iii) Rapid frequency - selective fading due to multipath propagation. It is the most severe

and governs the outage of analogue and digital radio links. Because the fading is

frequency selective, the distortion induced at all amplitude levels in a wideband digital

link can be a major source of outage. Multipath propagation reduces the cross-

polarization isolation in a dual-polarized link.

Conditions for fade types (ii) and (iii) occur during the night and early morning

hours of summer days in the temperate climates. In the tropics (especially at the costal

locations), the fades have a higher incidence of occurrence.


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2.5 Review of work done on Radio refractivity

Various researchers have one way or the other done various work on refractivity which

helps in the determination of information use in he design of communication link. Listed

below are some of the early researchers:

Kolawole and Owolabi (1982) have computed the vales of surface refractivity for

Africa, using meteorological data for 202 stations for 1978 1979. To remove the

dependence on elevation, surface values were reduced to sea level values No. A

refractivity scale height value of H = 7km obtained for tropical conditions by

Kolawole (1980) was adopted. Bean Thayer (1963) showed that the surface radio refractivity could be used to

estimate both radio range errors and elevation angle errors between radio links.

Willoughby (1997) made statistical analysis of regional and seasonal characteristics

of radio refractive index gradients in the first kilometer of a tropical atmosphere over

four meteorological stations in the West African sub-region, namely, Oshodi, a

coastal area, Minna, a savannah area, Kano and Niamey, both sub-sahelian regions.

He utilized data obtained from daily ascents made at noon. Based on these data, daily

values of refractivity gradient, their monthly means, standard deviations and

frequency distributions were computed to ascertain seasonal mean values. He also

analyzed the correlation coefficients between monthly means of refractivity at the

surface level, Ns, and the monthly means of refractivity decrease in the first kilometer

above ground. He also examined the seasonal behaviour of the dry and wet

components of the gradients.


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CHAPTER THREE

METHODOLOGY

3.1 Data Collection

The data needed for this research work are pressure, temperature and relative

humidity. Three regions are selected and they are; Lagos (Oshodi) - a coastal area ,

Minna - a savannah region and Kano- a sub-sahelian region. The daily measurement of

pressure, temperature and relative humidity for the three regions were obtained from the

Nigeria Meteorological Centre in Oshodi (NIMET) which is the headquarter providing

meteorological services in Nigeria. The data gotten were for a period of eight years(1998-2005), though the initial aim was to get the data for a period of ten years (1997-

2006) which could not be obtained due to logistic problems. The parameters gotten were

each converted to the appropriate units for the calculation and analysis involved.

For the pressure which is defined as force per unit area, the unit of the pressure

variable collected is in percentage (%). The temperature, which is the degree of coldness

or hotness of a medium, is measured, in degree Celsius (C). This can be converted to

absolute temperature which is in degree Kelvin. The relationship between the absolute

temperature and the measured one is as follow:

Temperature (K) = Temperature (C) + 273 (3.1)

Relative humidity can be defined as the amount of water content in the atmosphere. The

value of water vapour used in the calculation from obtained from the equation given

below [8] :

Pv = 0.01 x 8 x 5854/T 6 x 10 (20 2050/T) (3.2)


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Its unit is in hecto-pascal (hpa). Where,

Pv = water vapour pressure

T = temperature

3.2 METHOD OF ANALYSIS

The sum and mean values of pressure, temperature and relative humidity for each of the

three radiosonde stations (lagos oshodi , Kano and Minna) are analysed using Microsoft

excel software package. The values of the monthly and yearly surface refractivity was

also derived using the Microsoft excel statistical application. By using equation 2.1.

In Microsoft excel the command line for the following parameters were gotten:

A. Product of A and B (A*B) = PRODUCT (A, B)

B. Sum of A and B (A+B) = SUM (A, B)

C. Power of A and 2 (A) = POWER (A, 2)

D. Power of A and -2 (A (POWER (A,-2 = (

E. Division of A and B (A/B) = A x B 1 = PRODUCT (A, POWER (B, -1))

Therefore, the equation 2.1 can be written as:

N=SUM(PRODUCT(77.6,B4,POWER(B3,1)),PRODUCT(373000,PRODUCT(0.01,B5,

5854,POWER(B3,-6),POWER(10,SUM(20,PRODUCT(-2050,POWER(B3,-

1))))),POWER(B3,-2))). (3.3 )

Where B1-B5 represent the columns and rows on the excel sheet where the values for

pressure, temperature and relative humidity is located.

The graph of the surface refractivity against the corresponding month of the year

was plotted in order to determine the seasonal and the regional variations.


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To derive the effect of pressure on surface refractivity, the graph of surface

refractivity was then plotted against pressure for the whole year using the values obtained

from the three radiosonde stations. From the graph, the seasonal, regional and yearly

variation of surface refractivity is estimated for the three radiosonde stations. To get the

regional variation of refractivity, we compare the analysed value of refractivity for Lagos,

Kano and Minna region. Sea level refractivity value was also obtained from equation

(1.1) which relates surface refractivity to height obtained at the three regions.

In conclusion, the effect of pressure on surface refractivity will be determined by

relating the value of surface refractivity to the monthly mean value of pressure obtainedfor Lagos, Kano and Minna region.

3.3 SAMPLE OF ANALYSED PARAMETERS

By taking Kano region, which is a sub-sahelian region as a case study. The following

values were measured:

For the month of January 2005,

Pressure (P) = 60.3 hpa

Temperature ( C) = 25.5

Applying equation 3.1, temperature in degree celcius was converted to an

absolute temperature (K).

Temperature (K) = 25.5 + 273

T (K) = 298.8 Kelvin

Relative humidity (H in %) is converted to water vapour pressure ( Pv) using the equation

(3.2) :


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These calculations are repeated until monthly values of refractivity for the eight years

considered at the three selected regions had been calculated. Tables for the calculated

value of surface refractivity are presented in the Appendix A.


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TABLE 4:1 Table of refractivity; keeping temperature, relative humidity constant and

varying pressure.

Number Temperature Humidity Pressure Refractivity

1 302 61 6 251.0

2 302 61 12 252.6

3 302 61 18 254.1

4 302 61 24 255.6

5 302 61 30 257.2

6 302 61 36 258.7

7 302 61 42 260.3

8 302 61 48 261.8

9 302 61 54 263.3

10 302 61 60 264.9

11 302 61 66 266.4

12 302 61 72 267.9


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TABLE 4.2 : Table of refractivity, keeping temperature, pressure constant and varying

relative humidity.


1 302 7 55 42.76

2 302 14 55 71.39

3 302 2155

100.0

4 302 28 55 128.6

5 302 35 55 157.3

6 302 42 55 185.9

7 302 49 55 214.5

8 302 56 55 243.2

9 302 63 55 271.8

10 302 70 55 300.4

11 302 77 55 329.0

12 302 84 55 357.7


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TABLE 4.3 Table of refractivity; keeping relative humidity, pressure constant and

varying temperature.


1 294 61 55 277.8

2 296 61 55 274.1

3 298 61 55 270.5

4 300 61 55 267.0

5 302 61 55 263.6

6 304 61 55 260.2

7 306 61 55 256.9

8 308 61 55 253.7

9 310 61 55 250.5

10 312 61 55 247.4

11 314 61 55 244.4

12 316 61 55 241.4


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4.3 EFFECT OF PRESSURE ON SURFACE REFRACTIVITY

Since pressure increases directly with height, the pressure in Ikeja is the lowest

because the surface height is low. The surface height of Ikeja is 128.55m. This is low

when compared to that of Minna, which is 259.59m and Kano which has the highest

surface level height of 475.8m.

It was observed that, though Ikeja had a very low pressure compared to Kano and

Minna, the effect of change in pressure relatively in the three regions is small. Therefore,

the effect of pressure on surface refractivity is relatively low as shown by table (4.1). The

graph comparing the variation of pressure, temperature and humidity with refractivity areshown in Appendix C.

4.4 SEASONAL VARIATION OF SURFACE REFRACTIVITY

With various season we have in Nigeria such as rainy and harmattan (wet and dry)

season, there is variation in seasonal refractivity in the three regions which is as a result

of difference in climatic conditions. Histograms showing the variation of refractivity with

the month of the year for each of the three stations are as shown in Appendix B.

From the seasonal variation observed in Ikeja region, the value of monthly

refractivity is at peak between the month of April and October which in Nigeria is the

rainy or wet season. After October, there is slight decrease of refractivity from the month

of November to march which is the harmattan or dry season.

The seasonal variation for Kano region which is a sub-sahelian region, the values

of monthly refractivity gradually rise between the month of May to October, which is a

slight difference from what was obtained at Minna which normally starts from April and


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4.5 REGIONAL VARIATION IN SURFACE REFRACTIVITY

By the fact that Ikeja is a coastal region, the water vapour content in the lower

atmosphere is higher. In Ikeja, the change in the refractivity value from one month to the

other is small compared to the kind of variation observed in kano and Minna.

For Minna which is a savannah region, the humidity of the atmosphere is not as

pronounced as that of Ikeja centre but the pressure is very high compared to the obtained

at Ikeja. For the yearly variation of refractivity in Minna, it has similar pattern of graph

for the period of eight years used as a case study (1998 to 2005). The measured value of

pressure for Ikeja is very small compared to Kano and Minna centres.Finally, for Kano region which has the relatively lowest value of refractivity, the

effect of high temperature in Kano is that it reduces the water content of the lower

atmosphere. The reason for higher pressure is due to the relative increase of pressure with

height which is 475.8m (higher compared to the regions).

Generally, sea level refractivity is much higher during the rainy season than in the

dry season. Seasonal variation of the refractivity depends on climatic condition. Western

Nigeria is more humid than northern Nigeria. As it is shown in equation (2.1) it is

obvious that the refractivity is greater in the rainy season than that in other seasons,

particularly in the coastal area.


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CHAPTER FIVE

CONCLUSION AND RECOMMENDATIONS

Seasonal and Regional variations of propagation conditions for Nigeria have been

studied using radiosonde data collected between 1998 to 2005 for three regions namely;

Kano, Minna, and Ikeja.Surface refractivity have been estimated and the effect of pressure

on refractivity determined.

Since pressure increases directly with height in the atmosphere, the pressure in

Ikeja is the lowest because the surface height is lowest. The surface height which is

128.55m is lower compared to that of Minna which is 259.59m and Kano which has thehighest surface level height of 475.8m. It was observed that, though Ikeja had a very low

pressure compared to Kano and Minna, the effect of change in atmospheric pressure is

minimal when compared to that of temperature and water vapour pressure.

With various season we have in Nigeria such as rainy and harmattan (wet and dry)

season, there is variation in seasonal refractivity in the three regions which is as a result

of difference in climatic conditions. Variation in season which occurs in the three region

used as case study results in differences in the value of atmospheric parameters which in

the end results in changes in the surface refractivity.

By the fact that the study was carried out for three regions which is Ikeja (coastal

region), Kano (sub-sahelian region), Minna (savanna region); the water content, pressure

and temperature of the various region differs with the atmospheric conditions. Ikeja

region has the highest water vapour content in the atmosphere, which implies greater

refractivity as observed from the result obtained from the study. Kano region has the

highest value of temperature, lowest water vapour content due to the dry atmosphere and


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this has the lowest value of refractivity compared to other station considered. Minna

which is in the savanna region has value of temperature, water vapour pressure and

atmospheric pressure that falls within the range for Ikeja and kano, it is however in a

closer range to that of Kano.

5.1 SUGGESTION FOR FUTURE WORK

(1) Other methods for the measurement of temperature, pressure and humidity profile

can be used other than radiosondes. For example the raman lidar measurement [9] can be

used, though the most commonly used method for the measurement of temperature andhumidity profiles is the use of radiosondes. The main benefit of lidar over radiosondes is

that measurements can be made continuously. Another substantial advantage is that the

direction of the measurements is well known, whereas the path of a radiosonde is affected

by the wind, which often varies with height. Disadvantages of lidar are that it is a more

complex technique than the use of radiosondes, both in its experimental equipment and

the measurement calibration process described above, and it cannot operate through

dense cloud.

(2) Future researchers should use more radiosonde stations in Nigeria for case study,

because refractivity is dependent on variations in weather parameters such as pressure,

temperature and water vapour pressure which changes with climatic conditions. By using

more radiosonde stations the significance of the study which is to determine information

required for design of communication links is achieved.

(3) A programming language that will aid in determining the surface refractivity from

the values of atmospheric measure should be used, which will aid in updating the surface


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refractivity as days, months and years pass-by without necessarily starting the computing

of the atmospheric values all over again.

In conclusion, the aim of the study which is to determine the effect of pressure on

the variation of refractivity in tropical region (Nigeria) is achieved and further studies can

be carried out in other tropical locations in Africa.


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REFERENCES

[1] Bayong Tjasyono HK and Djakawinata S (1999) The Influence of

Meteorological Factors on Tropospheric Refractive Index over Indonesia , from

http://www.google.com , page 1-12, Retrieved June 15, 2007.

[2] Skolnik, M. I. (1962), "Introduction to Radar System", McGraw - Hill, New

York.

[3] Pavel Valtr and Pavel Pechac (2005), Remote sensing of refractivity profile

using angle of arrival spectra, Technicka 2, 166 27 Praha 6, Czech Republic, pp

1-4.[4] Kolawole L.B. and Owonubi J.J (1982), "The surface radio refractivity over

Africa", Nigerian Journal of Science 16, pp 441-454.

[5] Bean B. and E. Dutton (1968): Radio meteorology , Dover Publications, 435 pp.

[6] Propagation of Radio Waves - Editors M.P.M Hall, L.W. Barclay, M.T. Hewitt,

Published by IEE 1996 ISBN 0 85296 819 1.

[7] G.O. Ajayi (1989), "Physics of the tropospheric radio propagation",International

Centre for Theoretical Physics, Trieste, Italy pp 1-28.

[8] CCIR, Conclusions of the Interim Meeting of Study Group 5 - Propagation in

non-ionized media, DOC 5/204-E (July, 1988).

[9] Final Report on Lidar Measurement of Tropospheric Radio Refractivity (June

2002), pp 1-2.
http://www.google.com/http://www.google.com/


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APPENDIX A

1.0 Table for the calculated values of atmospheric parameters for Ikeja region.

TABLE 1.1 (Ikeja 1998)

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

TEMPERATURE 304 307 307 306 304 303 301 301 301 302 304 304

PRESSURE 5.1 5.9 4.1 4 6.2 7.9 8.1 7.7 7.4 6.3 4.4 4.8

HUMIDITY 49 54 54 62 70 73 76 72 78 76 66 61

CALCULATEDNo 273 319 323 365 391 392 391 370 404 404 362 339

CALCULATEDNs 268 313 317 358 384 385 384 364 397 397 356 333


JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DECTEMPERATURE 304 305 305 304 303 302 300 301 301 301 304 304

PRESSURE 4.0 4.1 3.2 4 .6 5.5 6.1 8.2 8.0 6.4 6.4 5.0 4.5

HUMIDITY 66 57 64 69 70 77 83 74 78 77 72 63

CALCULATEDNo 363 322 362 379 383 401 418 381 400 399 395 345

CALCULATEDNs 357 316 355 372 376 395 411 374 393 392 389 339



TEMPERATURE 304 306 307 305 304 273 301 300 300 303 304 304

PRESSURE 3.8 5.1 3.5 4 .1 5.4 7.1 7.4 8.4 6.7 6.2 4.6 5.2

HUMIDITY 63 39 58 64 70 78 75 80 84 73 69 62

CALCULATEDNo 353 225 343 364 384 177 387 401 423 391 384 345

CALCULATEDNs 347 221 337 357 377 174 380 394 415 385 377 339



TEMPERATURE 304 306 307 305 303 301 301 300 301 303 304 304PRESSURE 5.5 4.9 5 5.4 6 7.9 8.6 10 8.1 7.5 6.7 5.9

HUMIDITY 65 59 59 69 73 81 79 80 78 73 72 69

CALCULATEDNo 360 342 349 392 399 413 402 397 400 394 396 383

CALCULATEDNs 354 336 343 386 392 406 395 390 393 387 389 376


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TEMPERATURE 304 306 306 305 304 302 300 300 301 302 304 305

PRESSURE 6.5 5.4 4.7 3 .9 5.9 7.9 8.9 8.7 7.9 6.6 6.3 6.4

HUMIDITY 51 60 62 69 71 78 84 78 77 77 72 57

CALCULATEDNo 286 347 361 389 395 407 426 395 398 405 398 323

CALCULATEDNs 281 341 355 382 388 400 419 388 391 398 391 318



TEMPERATURE 304 306 306 304 304 301 301 301 302 303 304 305

PRESSURE 6.2 4.9 4.7 5 .2 6.1 7.2 8.9 8.7 7.9 5.7 4.9 5.4

HUMIDITY 68 66 63 68 70 80 74 72 77 74 71 59CALCULATEDNo 374 380 364 381 390 414 383 375 403 402 397 337

CALCULATEDNs 367 373 358 374 383 407 376 369 396 395 390 331



TEMPERATURE 305 305 306 304 302 302 301 300 301 303 304 305

PRESSURE 4.6 5.4 4.7 5 .4 6.8 8.9 8.6 8.4 7.8 7.0 6.0 5.3

HUMIDITY 62 60 60 73 79 77 76 77 79 77 71 67

CALCULATEDNo 349 340 346 402 419 404 390 386 407 416 392 378

CALCULATEDNs 343 334 340 395 412 397 383 379 400 409 385 372



TEMPERATURE 304 303 306 305 303 301 300 301 301 303 304 305

PRESSURE 6.0 4.2 5.2 5 .1 6.5 7.6 9.2 8.9 8.2 7.2 5.5 4.6

HUMIDITY 49 66 65 69 77 82 81 73 80 76 72 68

CALCULATEDNo 275 359 374 393 414 425 409 373 1 405 401 382

CALCULATEDNs 270 353 368 387 407 417 402 366 405 398 394 375


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2.0 Table for the calculated values of atmospheric parameters for Minna region.

TABLE 2.1 (Minna 1998)


TEMPERATURE 305 310 309 308 305 303 301 300 301 304 308 307

PRESSURE 80.4 80.2 78.8 77.9 79.8 81.4 81.3 81.0 80.9 81.1 78.9 79.8

HUMIDITY 27 21 20 17 64 69 77 79 74 65 33 29

CALCULATEDNo 177 156 148 127 387 398 421 425 412 384 223 195

CALCULATEDNs 171 150 143 122 373 384 406 410 398 370 216 188



TEMPERATURE 306 307 308 308 305 303 301 300 301 303 307 307

PRESSURE 79.1 78.5 76.9 78.4 79.8 80.5 81.5 81.6 80.5 80.4 79.2 79.4

HUMIDITY 25 50 44 42 58 66 75 79 75 66 36 30

CALCULATEDNo 169 326 294 278 353 380 409 422 412 383 239 200

CALCULATEDNs 163 315 283 268 341 367 395 407 398 370 231 193



TEMPERATURE 306 305 308 308 306 302 301 300 301 303 307 306

PRESSURE 78.5 80.4 77.9 78.0 79.3 81.0 81.1 81.9 80.5 80.5 78.8 80.1

HUMIDITY 50 22 28 50 57 71 76 79 76 65 33 33

CALCULATEDNo 318 149 195 328 355 398 413 424 421 379 221 217

CALCULATEDNs 307 144 188 317 342 384 399 409 407 366 214 209



TEMPERATURE 306 307 309 307 305 302 300 300 301 305 308 308

PRESSURE 80.2 79.3 78.4 78.5 79.8 81.4 81.6 82.4 81.0 80.3 79.7 79.3


CALCULATEDNs 156 154 260 350 358 381 397 408 386 308 210 239


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TEMPERATURE 304 308 309 306 306 303 301 301 301 303 273 306

PRESSURE 80.5 79 78 77 79 81 82 82 81 80.1 80 81

HUMIDITY 20 23 37 55 64 66 76 76 72 65 31 26

CALCULATEDNo 135 162 255 348 402 383 417 415 401 375 94.3 175

CALCULATEDNs 130 157 246 336 388 370 402 400 387 362 91 169



TEMPERATURE 306 309 310 307 306 302 301 300 301 304 307 306

PRESSURE 80.3 79.0 78.5 78.7 79.4 80.7 81.8 81.5 81.2 79.3 78.7 79.5

HUMIDITY 32 32 31 49 54 71 75 78 73 66 37 23

CALCULATEDNo 212 222 220 319 341 401 411 423 404 392 244 157

CALCULATEDNs 204 214 212 308 329 387 397 408 390 378 236 151



TEMPERATURE 306 308 309 307 304 302 301 300 302 304 306 307

PRESSURE 78.8 79.4 78.5 78.3 80.0 82.1 81.3 82.1 80.8 80.0 79.0 78.6

HUMIDITY 24 21 26 54 65 91 71 77 71 65 45 24

CALCULATEDNo 163 149 186 350 385 505 394 412 398 383 285 166

CALCULATEDNs 157 144 179 338 372 488 381 397 384 369 276 160



TEMPERATURE 305 309 310 308 305 302 300 300 302 303 307 307

PRESSURE 79.9 77.3 78.1 78.2 79.6 80.7 82.0 81.6 81.2 80.3 78.7 77.9

HUMIDITY 20 31 36 46 61 70 76 74 71 64 33 26

CALCULATEDNo 135 217 252 305 369 398 412 401 403 372 221 176

CALCULATEDNs 131 209 243 294 356 384 397 387 389 359 213 170


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3.0 Table for the calculated values of atmospheric parameters for Kano region.

TABLE 3.1 (Kano 1998)


TEMPERATURE 300 304 305 311 310 305 302 301 303 306 306 301

PRESSURE 60.3 60.3 59 56 56.7 59 58.4 58 58.1 58 58 59

HUMIDITY 25 17 31 15 39 55 68 72 67 42 24 19

CALCULATEDNo 147 116 199 119 275 345 396 408 393 273 160 119

CALCULATEDNs 137 109 186 111 257 323 370 381 367 255 150 111



TEMPERATURE 301 304 310 310 309 308 301 301 303 305 306 300

PRESSURE 59 57.6 55 56 56.8 57 58.5 59 58 58 58 58

HUMIDITY 18 17 13 17 31 40 70 71 65 41 17 60

CALCULATEDNo 114 116 101 130 221 269 397 397 384 261 119 333

CALCULATEDNs 106 108 95 121 206 251 370 371 358 244 112 311



TEMPERATURE 302 299 306 312 310 305 302 302 304 306 306 301

PRESSURE 57.9 60.7 57 54 55.4 57 57.3 58 57.2 58 57 60HUMIDITY 17 15 13 17 30 54 64 68 61.3 39 20 20

CALCULATEDNo 109 93.7 94 133 215 336 372 389 370 252 136 124

CALCULATEDNs 102 87.5 88 124 201 314 348 364 345 236 127 115



TEMPERATURE 300 301 308 308 308 304 302 301 303 306 305 302

PRESSURE 60.0 59.0 57.1 55.4 56.3 57.7 58.0 59.1 57.9 58.3 58.7 58.9


CALCULATEDNs 177 110 74 162 269 329 354 376 358 174 98 108


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TEMPERATURE 299 302 308 311 311 307 304 302 303 304 305 302

PRESSURE 61.1 59.4 57.1 54.4 56.1 57.7 58.7 58.7 58.2 58.0 58.9 60.3

HUMIDITY 17 15 15 24 27 45 59 67 62 43 19 17

CALCULATEDNo 103 98.5 111 178 201 294 355 387 370 268 128 109

CALCULATEDNs 96.2 92 104 166 187 275 332 361 346 250 120 102



TEMPERATURE 301 304 306 311 310 304 302 302 303 307 306 300

PRESSURE 60.0 58.6 58.3 56.1 56.9 58.2 59.0 58.9 58.7 57.4 58.1 59.8

HUMIDITY 19 13 31 22 27 59 66 69 63 39 24 25CALCULATEDNo 119 92.3 207 165 195 356 382 397 375 260 161 149

CALCULATEDNs 111 86.3 193 154 183 332 357 371 351 242 150 139



TEMPERATURE 301 302 305 311 308 305 302 302 304 307 305 303

PRESSURE 58.9 59.9 58.2 56.0 56.9 58.6 58.6 58.9 58.0 57.8 58.1 58.4

HUMIDITY 14 13 11 24 44 54 65 67 61 27 23 26

CALCULATEDNo 91.4 87.7 82 178 298 334 376 385 371 186 154 162

CALCULATEDNs 85.4 81.9 77 167 278 312 351 360 347 174 144 151



TEMPERATURE 299 307 309 311 308 305 302 301 304 305 305 303

PRESSURE 60.3 57.2 57.4 56.1 57.3 58.0 59.1 58.7 58.5 58.2 58.2 57.9

HUMIDITY 18 13 11 20 35 54 67 70 60 41 17 17

CALCULATEDNo 108 96.4 88 151 241 335 388 395 368 261 116 111

CALCULATEDNs 101 90.1 82 141 225 313 362 369 344 244 109 104


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APPENDIX B

1.0 Chart of surface refractivity against month of the year for Ikeja region.

FIGURE 1.1.1

FIGURE 1.1.2

FIGURE 1.1.3

IKEJA (2005)

0

100

200

300

400

500


Month of the year

S u r f a c e r e

f r a c

t i v

i t y

IKEJA (2003)

0

100

200

300

400

500


Month of the year

s u r f a c e r e

f r a c

t i v

i t y

IKEJA (2004)

0

100

200

300

400

500


Month of the year

S u r f a c e r e

f r a c

t i v

i t y

IKEJA (2004)

0

100

200

300

400

500


Month of the year

S u r f a c e r e

f r a c

t i v

i t y


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FIGURE 1.1.4

FIGURE 1.1.5

FIGURE 1.1.6

IKEJA (2002)

050

100150200250300350400450


Month of the year

S u r f a c e r e

f r a c

t i v

i t y

IKEJA (2001)

0

100

200

300

400

500


Month of the year

S u r f a c e r e

f r a c

t i v

i t y

IKEJA (2000)

050

100150

200250300350400450


Month of the year

S u r f a c e r e

f r a c

t i v

i t y


56/80


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FIGURE 1.2.2

FIGURE 1.2.3

FIGURE 1.2.4

IKEJA (2004)

0.0

2.0

4.0

6.0

8.0

10.0

JA N FEB MA R APR MAY JUN JUL AUG SEP OCT NOV DEC

month of the year

p r e s s u r e

IKEJA (2002)

0.0

2.0

4.0

6.0

8.0

10.0


month of the year

p r e s s u r e

IKEJA (2003)

76.0

77.0

78.0

79.0

80.0

81.0

82.0

83.0


month of the year

p r e s s u r e


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FIGURE 1.2.5

FIGURE 1.2.6

FIGURE 1.2.7

IKEJA (2001)

0

2

4

6

8

10

12

JA N FEB MA R A PR MAY JUN JUL A UG SEP OCT NOV DEC

month of the year

p r e s s u r e

IKEJA (2000)

0.0

2.0

4.0

6.0

8.0

10.0


month of the year

p r e s s u r e

IKEJA (1999)

0.01.02.03.04.05.06.07.08.09.0


month of the year

p r e s s u r e


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FIGURE 1.2.8

2.1 Chart of surface refractivity against month of the year for Minna region.

FIGURE 2.1.1

FIGURE 2.1.2

IKEJA (1998)

0

2

4

6

8

10

JAN FEB MAR APR MAY JUN JUL A UG SEP OCT NOV DEC

month of the year

p r e s s

u r e

MINNA (1998)

0

100

200

300

400

500


month of the year

r e f r a c t i v

i t y

MINNA (1999)

74.0

76.0

78.0

80.0

82.0


month of the year

s u r f a c e r e

f r a c

t i v

i t y


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FIGURE 2.1.3

FIGURE 2.1.4

FIGURE 2.1.5

MINNA (2000)

75.076.077.078.079.080.0

81.082.083.0


month of the year

s u r f a c e r e

f r a c

t i v

i t y

MINNA (2001)

76.0

77.078.079.0

80.081.082.0

83.0


month of the year

s u r f a c e r e

f r a c

t i v

i t y

MINNA (2002)

74

76

78

80

82

84

JAN FEB MAR A PR MAY JUN JUL AUG SEP OCT NOV DEC

month of the year

s u r f a c e r e

f r a c

t i v

i t y


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FIGURE 2.1.6

FIGURE 2.1.7

FIGURE 2.1.8

MINNA (2003)

76.0

77.0

78.0

79.0

80.0

81.0

82.0

83.0


month of the year

s u r

f a c e r e

f r a c

t i v

i t y

MINNA (2004)

76.0

77.0

78.0

79.0

80.0

81.0

82.0

83.0

JA N FEB MA R A PR MAY JUN JUL A UG SEP OCT NOV DECmonth of the year

s u r f a c e r e

f r a c

t i v

i t y

MINNA (2005)

74.075.076.077.078.0

79.080.081.082.083.0


month of the year

s u r f a c e r e

f r a c

t i v

i t y


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2.2 Chart of pressure against month of the year for Minna region.

FIGURE 2.2.1

FIGURE 2.2.2

FIGURE 2.2.3

MINNA (1998)

76.0

77.0

78.0

79.0

80.0

81.0

82.0


month of the year

p r e s s u r e

MINNA (1999)

74.075.076.077.078.079.080.081.082.0


month of the year

p r e s s u r e

MINNA (2000)

74.0

76.078.080.082.084.0


month of the year

p r e s s u r e


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FIGURE 2.2.4

FIGURE 2.2.5

FIGURE 2.2.6

MINNA (2001)

76.0

77.0

78.079.0

80.0

81.0

82.0

83.0


month of the year

p r e s s u r e

MINNA (2002)

757677787980818283


month of the year

p r e s s u r e

MINNA (2003)

76.0

77.0

78.0

79.0

80.0

81.0

82.0

83.0


month of the year

p r e s s u r e


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FIGURE 2.2.7

FIGURE 2.2.8

3.1 Chart of surface refractivity against month of the year for Kano region.

FIGURE 3.1.1

MINNA (2004)

76.0

77.078.079.080.081.082.083.0


month of the year

p r e s s u r e

MINNA (2005)

74.0

76.0

78.0

80.0

82.0

84.0


month of the year

p r e s s u r e

KANO (1998)

050

100150200250300350400450


month of the year

s u r f a c e r e

f r a c

t i v

i t y


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FIGURE 3.1.2

FIGURE 3.1.3

FIGURE 3.1.4

KANO (1999)

050

100150

200250300350400


month of the year

s u r f a c e

r e f r a c

t i v

i t y

KANO (2000)

050

100150200250300350400


month of the year

s u r f a c e r e

f r a c

t i v

i t y

KANO (2001)

050

100

150200250300350400


month of the year

s u r

f a c e r e

f r a c

t i v

i t y


66/80

66

FIGURE 3.1.5

FIGURE 3.1.6

FIGURE 3.1.7

KANO (2002)

050

100150200250300350400


month of the year

s u r f a c e r e

f r a c

t i v

i t y

KANO (2003)

050

100150200250300350400


month of the year

p r e s s u r e

KANO (2004)

050

100

150200

250300350400


month of the year

s u r

f a c e r e

f r a c

t i v

i t y


67/80


68/80

68

FIGURE 3.2.3

FIGURE 3.2.4

FIGURE 3.2.5

KANO (2000)

5052

5456

5860

62


month of the year

p r e s s u r e

KANO (2001)

53.054.055.056.057.058.059.060.061.0


month of the year

p r e s s u r e

KANO (2002)

50.0

52.0

54.0

56.0

58.0

60.0

62.0


month of the year

p r e s s u r e


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69

FIGURE 3.2.6

FIGURE 3.2.7

FIGURE 3.2.8

KANO (2003)

54.055.056.057.058.0

59.0

60.061.0


month of the year

p r e s s u r e

KANO (2004)

54.055.056.057.058.059.060.061.0


month of the year

p r e s s u r e

KANO (2005)

54.0

55.056.0

57.0

58.0

59.0

60.0

61.0


month of the year

p r e s s u r e


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70

APPENDIX C Graph showing variation of surface refractivity with temperature, pressure and

humidity in Ikeja.

Figure 1.1

Figure 1.2

Figure 1.3

IKEJA (1998)

050

100150200250300350400450

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

Temperature

Pressure

Humidity

Surface refractivity

IKEJA (2000)

050

100150200250300350400450

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

temperature

pressure

humidity

surface r efractivity

IKEJA (1999)

050

100150200250300350400450

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

temperature

pressure

humidity

surface refractivity


71/80

71

Figure 1.4

Figure 1.5

Figure 1.6

IKEJA (2001)

050

100150200250

300350400450

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

Temperature

PressureHumidity

Surface Refractivity

IKEJA (2002)

0

50

100

150

200

250

300

350

400

450

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

temperature

pressure

humidity


0

50

100150

200

250

300

350

400

450

0.0 5.0 10.0 15.0

temperature

pressure

humidity



72/80

72

Figure 1.7

Figure 1.8

2.0 Graph showing variation of surface refractivity with temperature, pressure

and humidity in Minna.

Figure 2.1

IKEJA (2004)

050

100150

200250300350400450

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

temperature

pressure

humidity


IKEJA (2005)

050

100150200250300350400450

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

temperature

pressure

humidity


MINNA (1998)

050

100150200250300350400450

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

temperature

pressure

humidity



73/80

73

Figure 2.2

Figure 2.3

Figure 2.4

MINNA (1999)

0

50

100

150

200

250

300

350

400

450

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

temperature

pressure

humidity


MINNA (2000)

050

100150200

250300350

400450

0.0 5.0 10.0 15.0

temperature

pressure

humidity


MINNA (2001)

050

100150

200

250300350

400450

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

temperature

pressure

humidity



74/80


75/80


76/80

76

Figure 3.3

Figure 3.4

Figure 3.5

KANO (2000)

0

50100

150

200250

300

350

400

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

temperature

pressure

humidity


KANO (2001)

0

50

100

150

200

250

300

350400

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

temperature

pressure

humidity


KANO (2002)

050

100

150

200

250

300

350

400

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

temperature

pressure

humidity



77/80

77

Figure 3.6

Figure 3.7

Figure 3.8

KANO (2003)

0

50

100

150

200

250

300

350

400

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

temperaturepressure

humidity


KANO (2004)

0

50

100

150

200

250

300

350

400

0.0 5.0 10.0 15.0

temperature

pressure

humidity


KANO (2005)

0

50

100

150

200

250

300

350

400

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0

temperature

pressure

humiditysurface r efractivity


78/80

78

GLOSSARY

A. Ducting: is the two boundary surface between layers of air or a short leaky

waveguides which guided the electromagnetic wave between its walls.

B. Multi-path: is the collection of sizable irregularies or layers of random

elevations. It occurs mostly on clear nights with little or no wind.

C. Troposphere: is defined as the lower part of the atmosphere in which

temperature decreases with altitude. It extends from the earths surface up to a

distance of the order of 10km.D. Radiosonde: is the meteorological station where data for atmospheric parameters

are detected, measured and analysed.

E. Surface-Refraction: occurs when a ray of electromagnetic wave is bent away

from the normal when it enters a less dense medium and that the deviation from

the normal increases as the angle of incidence increases.

F. Sub-refraction: this occurs when ray of electromagnetic wave is bent towards the

normal.


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onaolapo olayinka

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