RADIO REFRACTIVITY AT ILORIN DERIVED FROM METEOROLOGICAL

PARAMETERS OBTAINED FROM AUTOMATIC WEATHER STATION

BY

AKINPADE AKINTUNDE SAMSON

Matric. NO: 12/55ED032

A RESEARCH PROJECT REPORT SUBMITTED TO THE DEPARTMENT OF

PHYSICS, FACULTY OF PHYSICAL SCIENCE, UNIVERSITY OF ILORIN, ILORIN,

NIGERIA, IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE AWARD

OF THE DEGREE OF BACHELOR OF SCIENCE

B. Sc (HONS) IN PHYSICS

SUPERVISED BY DR. O.A FALAIYE

AUGUST 2016.

CERTIFICATION

This is to certify that this project work has being read, supervised and approved as fulfilling

the requirement of the Department of Physics University of Ilorin, Kwara State for the award of

Bachelor of Science (B.sc) Degree in Physics.

………………………… ………………………..

Dr. O.A. FALAIYE Date

Project Supervisor

………………………… ……………………….

Dr. O.A. Oladipo Date

Head of Department

……………………….. ..……………………..

Prof. (Mrs). A.O. Boyo

External Examiner Date

DEDICATION

This project Work is dedicated to Almighty God, my beloved parents, Mr. and Mrs. AKINPADE

which through their help I was able to make this work a success.

ACKNOWLEDGEMENT

Thanks, praises, total submission and glorification are due to Almighty God, who in His infinite

mercy guide, protect me and grant me success throughout my academics pursuit.

I wish to express my sincere gratitude and appreciation to my supervisor Dr. O.A. Falaiye who

despite his very tight schedule provided guidance, inspiration, supervision, constructive criticism

and fatherly advice, encouragement, contributions and suggestions to making this project come

out beautifully. I really thank him for making this work a success, and this is highly appreciated

and would continue to be remembered.

My profound gratitude goes to the Head of Department Dr. O.A. Oladipo, lecturers in the

Department of Physics, University of Ilorin and Mr. Johnson Abimbola (Federal University Lafia)

who also assisted me in one way or the other in making this work a success.

I will not forget to extend my gratitude, thanks and appreciation to my parents Mr. and Mrs.

AKINPADE who prayed for me every night and day to see that this work is a success. Indeed they

have contributed immensely toward making my dreams come true.

Finally I will like to express my sincere appreciation to my friend Olaniyi Bukola (Bae), Adesanya

Adeyinka, Afolabi Oluwakemi and my colleagues in the Department of Physics especially

shodunke Olasunkanmi, Adebisi Sheriff (choco-boy), Gbadamosi Taiwo, Ayoola Adekunle

(santy), Adeniji Oluwaseun (Baba Ibadan), Odubiyi Ololade, Tenabe Bidemi, and my noisy

neighbours (Falola IsZak, Monsuraht, Ade and others) for their encouragement toward making

this work a success. May almighty God reward every one of them abundantly Amen.

AKINPADE AKINTUNDE SAMSON.

TABLE OF CONTENTS

Title page

Certification

Dedication

Acknowledgement

Table of content

List of figures

Abstract

CHAPTER ONE

1.0 Introduction

1.1 Aims and Objectives

1.2 Significance of the Study

1.3 Atmospheric Pressure

1.4 Refractivity index gradient

CHAPTER TWO

2.0 Literature review

2.1 Atmospheric pressure

2.2 Temperature

2.3 Relative humidity

CHAPTER THREE

Methodology and Data Collection

3.1 Materials and Method

3.2 Location and Instrumentation set-up

3.3 Procedure of administering the instrument

CHAPTER FOUR

4.0 Analysis and Interpretation of result

4.1.1 Hourly Variation of Radio Surface Refractivity for one day (19/04/2016)

4.1.2 Hourly Variation of Radio Surface Refractivity for one day (06/05/2016)

4.1.3 Hourly Variation of Radio Surface Refractivity for one day (30/05/2016)

4.1.4 Weekly Variation of Radio Surface Refractivity.

4.1.5 Diurnal Variation of Relative humidity

4.1.6 Diurnal Variation of Temperature.

4.1.7 Hourly Variation of Radio Surface Refractivity (morning hour)

4.1.8 Hourly Variation of Radio Surface Refractivity (evening hour)

4.1.9 Diurnal Variation of Surface Refractivity (first 15-days)

4.2.0 Diurnal Variation of Surface Refractivity (last 15-days)

4.2.1 Variation of Surface Radio Refractivity and Relative humidity with time

4.2.2 Variation of Surface Radio Refractivity and Temperature with time

4.2.3 Linear Regression on Surface Radio Refractivity and Surface Relative Humidity.

4.2.4 Linear Regression on Surface Radio Refractivity and Surface Dew point temperature

4.2.5 Linear Regression on Surface Radio Refractivity and temperature

4.26 Refractive index gradient

CHAPTER FIVE

Conclusion and Recommendation

5.1 Conclusion

5.2 Recommendation

Reference

List of Figures

Figure

3.1 Diagram showing the Automatic Weather Station and Data Logger

3.2 Diagram of researcher taking the meteorological parameters from automatic weather station

3.3 Diagram of researchers taking reading of meteorological parameter using automatic weather

station

4.1.1 Diagram of the hourly variation of radio surface refractivity for one

day (19/04/2016)

4.1.2 Diagram of the hourly variation of radio surface refractivity for one

day (06/05/2016)

4.1.3 Diagram of the hourly variation of radio surface refractivity for one

day (30/05/2016)

4.1.4 Diagram showing comparison of diurnal variation of surface

refractivity with time from week 1-6 of April and May 2016

4.1.5 Diagram showing the diurnal plot of relative humidity variation

4.1.6 Diagram showing the diurnal plot of temperature variation

4.1.7 Diagram showing the diurnal variation of radio surface refractivity

for morning (19/04/2016) between 7am to 2pm

4.1.8 Diagram showing the hourly variation of radio surface refractivity

for evening (19/04/2016) between 4pm to 7pm

4.1.9 Diagram showing diurnal variation of radio surface refractivity for first 15-days (12/04/2016)

to (26/04/2016)

ABSTRACT

This project investigates the effect of diurnal variations of meteorological parameters on the

tropospheric radio refractivity during rainy seasons for Ilorin (University of Ilorin, kwara State,

Nigeria) between April and May 2016. Hourly data of meteorological variables with sampling time

of 5mins for 53 days collected within the months of April and May was used for this project. The

hourly mean of radio refractivity during rainy (April and May) seasons were calculated from the

data obtained from the Automated Weather Station (WH109C 433MHZ).

It was found that surface radio refractivity over Ilorin is usually/normally high ranging from 360-

390 N-units in the morning hours and from 365-385 N-units in the evening but decreases to a

minimum 350 – 365 N units in the afternoon. The results indicated that the hourly averages of

radio refractivity during rainy season is more significant owing to the increase in temperature and

humidity. Variations of meteorological parameters such as humidity and temperature in the lower

troposphere causes the radio refractivity to vary at different time of the day. The value of refractive

index gradients computed showed that the atmosphere over Ilorin was super-refractive during the

rainy season.

CHAPTER ONE

INTRODUCTION

The propagation of radio wave signal in the troposphere is affected by many processes which

include the variation of meteorological parameters such as temperature, pressure and humidity.

These are associated with the change in weather in different seasons of the year. These variations

in meteorological parameters have resulted in refractivity changes. According to Grabner and

Kvicera (2008), multipath effects also occur as a result of large scale variations in atmospheric

radio refractive index, such as different horizontal layers having different refractivity. This effect

occurs most often, when the same radio wave signals follow different paths thereby having

different time of arrivals to its targeted point. This may result to interference of the radio wave

signals with each other during propagation through the troposphere. The consequence of this large

scale variation in the atmospheric refractive index is that radio waves propagating through the

atmosphere become progressively curved towards the earth. Thus, the range of the radio waves is

determined by the height dependence of the refractivity. Thus, the refractivity of the atmosphere

will not only vary as the height changes but also affect radio signal. The quality of radio wave

signal reception and probability of the failure in radio wave propagations are largely governed by

radio refractivity index gradient which is a function of meteorological parameters changing in

lower atmosphere such as temperature, pressure and humidity (Sarkar 1978; Judd 1985). Radio

waves travel through vacuum with a speed equal to the speed of light. In material medium, the

speed of the radio waves is approximately c/n where c is the speed of light in vacuum and n is the

radio refractive index of the medium. The value of radio refractive index (n) for dry air is almost

the same for radio waves and the light waves. But the value of radio refractive index (n) for water

vapor, which is always present in some quantity in the lower troposphere, is different for the light

waves and radio waves. This arises from the fact that water vapor molecule has a permanent dipole

moment which has different responses to the electric forces of different radio wave frequencies

propagated within the atmosphere. Radio–wave propagation is determined by changes in the

refractive index of air in the troposphere (Adediji and Ajewole 2008). Changes in the value of the

troposphere radio refractive index can curve the path of the propagating radio wave. At standard

atmosphere conditions near the Earth’s surface, the radio refractive index is equal to approximately

1.0003 (Freeman, 2007). Since the value of refractive index is very close to unity, then the

refractive index of air in the troposphere is often measured by a quantity called the radio-

refractivity N, which is related to refractive index, n as:

N = (n-1) × 106

As the conditions of propagation in the atmosphere vary, the interference of radio-wave

propagation is observed. Such interferences are incident with some meteorological parameters

(inversion of temperature, high evaporation and humidity, passing of the cold air over the warm

surface and conversely), (Valma. et al, 2010). The atmospheric radio refractive index depends on

air temperature, humidity, atmospheric pressure and water vapour pressure. Subsequently,

meteorological parameters depend on the height at a point above the ground surface. Variation in

any of these meteorological parameters can make a significant variation on radio wave

propagation, because radio signals can be refracted over whole signal path (Priestley and Hill,

1985). In the atmosphere, pressure, temperature and humidity decrease exponentially as height h

increases (Falodun and Ajewole, 2006). According to Willoughby (2002), atmosphere has an

important feature:- the vertical gradient of the refractive index, G. The vertical gradient of the

refractive index is responsible for bending of propagation direction of the electromagnetic wave.

If the value G is negative, the signal bends downward (Guanjun and Shukai, 20004). The

characterization of the seasonal variation in fading and its dependence on meteorological

parameters provides the way to improve transmission performance by better tailoring of

performance

equipment design and usage to the amount of fading expected at a given location and time of the

year. This work is, therefore, aimed at finding out the

diurnal variation of meteorological parameters with the tropospheric radio refractivity in rainy

seasons at Ilorin (University of Ilorin, kwara, State.) between April and May 2016.

The vertical gradient of radio refractivity in the lower layer of the atmosphere is an important

parameter in estimating path clearance and propagation effects such as sub-refraction, super-

refraction, or ducting according to the following:

- Sub refraction : 𝑑𝑁

𝑑𝑍> -40

Radio refractivity N increases with height and in this case (sub-refraction), the radio wave

moves away from the earth’s surface and the line of sight range and the range of

propagation decrease accordingly.

- Super-refraction: 𝑑𝑁

𝑑𝑍< −40

During super-refractive conditions, electromagnetic waves are bent downward towards the

earth. The degree of bending depends upon the strength of the super refractive condition.

The radius of curvature of the ray path is smaller than the earth’s radius and the rays leaving

the transmitting aerial at small angles of elevation will undergo total internal reflection in

the troposphere and it will return to the earth at some

distance from the transmitter. On reaching the earth’s surface and being reflected from it,

the waves can skip large distances, thereby giving abnormally large ranges beyond the line

of sight due to multiple reflections.

- Ducting: : 𝑑𝑁

𝑑𝑍< −157

During ducting phenomenon, the waves bend downwards with a curvature greater than that

of the earth. Radio energy bent downwards can become trapped between a boundary or

layer in the troposphere and the surface of the earth or sea (surface duct) or between two

boundaries in the troposphere (elevated duct). In this wave guide-like propagation, very

high strengths can be obtained at very long range (far beyond line-of-sight) and the signal

strength may exceed its free-space value.

Radio waves travel through vacuum with a speed equal to the speed of light. In any other medium,

the speed of the radio waves will be nearly 𝑐⁄𝑛 where c is the speed of light in vacuum and n is the

radio refractive index of the medium. The value of n for dry air is almost the same for radio waves

and the light waves. But the ‘n’ of water vapour, which is always present in some quantity in the

lower troposphere, is different for the light waves and radio waves. This arises from the fact that

water vapour molecule has a permanent dipole moment which has different responses to the

electric forces of different responses to the electric forces of different frequencies and at

microwave frequencies water vapour molecules are subjected to electronic polarization. Hence,

for these frequencies, than that of dry air. The radio refractive index n for moist air near the surface

has the value of the order of 1.0003 and the variation in n is only of the order of few parts in104

Direct measurement of n for microwave frequencies; make use of resonance of tuned circuits. The

resonant frequency of a microwave cavity is a function of its dimensions and the index of refraction

of its contents. If a cavity is open to the atmosphere, the resonant frequency changes with the n of

the air inside the cavity as

∆𝑓

𝑓 = −

∆𝑛

𝑛

Where f is the resonant frequency of the cavity when filled with air of refractive index n, ∆f is the

consequent change in f as a result of the change of n for air is of the order of unity,

∆𝑓

𝑓 = −∆𝑛

The value of n at surface or near the surface is measured indirectly by measuring temperature,

pressure and humidity which are standard observations recorded by the meteorological services.

Even though the refract-meters may be capable of superior accuracy but the high cost and

requirements of competent personnel for running a network of such observing stations seem to

outweigh this advantage. Also, for long term studies, the use of refract-meters may not be essential.

Hence generally for all average conditions, the data on radio refractive index computed from

meteorological parameters is sufficient.

1.1 AIMS AND OBJECTIVES

To determine the Radio refractivity during rainy season within April 12, (2016) and May

30, 2016 for Ilorin (UNILORIN)

To investigate the relationship among temperature, pressure and relative humidity.

To study the variation of temperature, pressure and relative humidity.

To determine Refractive index gradient.

1.2 SIGNIFICANCE OF THE STUDY

The significance of the study is to characterize the diurnal variation of the meteorological

parameters (pressure, temperature and relative humidity) with the tropospheric radio

refractivity in rainy season which occurred within the period of observation that is between

April 19, 2016 and May 30, 2016 and to analyze the variation of Radio Refractivity with

respect to temperature, pressure and relative humidity and also to determine the refractive

index gradient.

1.4 REFRACTIVE INDEX GRADIENT

One of the most significant factors in the influence of radio wave propagation is the large scale

variation of refractive index with height and the extent to which this change with time (Hall,

1979). The refractive index gradient is the rate of change of N with altitude. Changes in the lapse

rate of N cause the curvature of radio ray information on the occurrence and type of gradients is

required of some propagation parameters. The measured median of the mean refractivity gradient

in the first kilometer above ground in most temperate region is about -40 N-units/km.

The change in radio refractivity 𝑑𝑁

𝑑𝐻=

𝑁1−𝑁𝑆

𝐻1 –𝐻𝑆

𝑤ℎ𝑒𝑟𝑒 𝑁1 𝑖𝑠 𝑡ℎ𝑒 𝑟𝑒𝑓𝑟𝑎𝑐𝑡𝑖𝑣𝑖𝑡𝑦 𝑎𝑡 𝑎 ℎ𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 1𝑘𝑚 𝑎𝑏𝑜𝑣𝑒 𝑡ℎ𝑒 𝑠𝑢𝑟𝑓𝑎𝑐𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑒𝑎𝑟𝑡ℎ, 𝑁𝑆 𝑖𝑠 𝑡ℎ𝑒

surface refractivity, 𝐻1 is the surface height above sea level and H1 is the height of 1km.

CHAPTER TWO

LITERATURE REVIEW

The propagation of radio wave signal in the troposphere is affected by many processes which

include the variations of meteorological parameters such as temperature, pressure and humidity.

These are associated with the change in weather in different seasons of the year. These variations

in meteorological parameters have resulted in refractivity changes.

According to ( Grabner and Kvicera (2008)), multipath effects also occur as a result of large scale

variation in atmospheric radio refractive index, such as different horizontal layers having different

refractivity. This effect occurs most often, when the same radio wave signals follow different paths

thereby having different time of arrivals to its targeted point. This may result to interference of the

radio wave signals with each other during propagation through the troposphere. The consequence

of this large scale variation in the atmospheric refractive index is that radio waves propagating

through the atmosphere become progressively curved towards the earth. Thus, the range of the

radio waves is determined by the height dependence of the refractivity. Thus, the refractivity of

the atmosphere will not only vary as the height changes but also affect radio signal. The quality of

radio wave signal reception and probability of the failure in radio wave propagations are largely

governed by radio refractivity index gradient which is a function of meteorological parameters

changing in lower atmosphere such as temperature, pressure and humidity (Sarkar, 1978; Judd,

1985). Radio waves travel through vacuum with a speed equal to the speed of light. In material

medium, the speed of the radio waves is approximately 𝑐⁄𝑛 where c is the speed of light in vacuum

and n is the radio refractive index of the medium. The values of radio refractive index (n) for dry

air are almost the same for radio waves and the light waves. But the value of radio refractive index

(n) for water vapour, which is always present in some quantity in the lower troposphere, is different

for the light waves and radio waves. This arises from the fact that a water vapour molecule has a

permanent dipole moment which has different responses to the electric forces of different radio

wave frequencies propagated within the atmosphere.

Radio-wave propagation is determined by changes in refractive index of air in the troposphere

(Adediji and Ajewole, 2008). Changes in the value of the troposphere radio refractive index can

curve the path of the propagating radio wave. At standard

atmosphere conditions near the Earth’s surface, the radio refractive index is equal to approximately

1.0003 (Freeman, 2007). Since the value of refractive index of air in the troposphere is often

measured by a quantity called the radio-refractivity N, which is related to refractive index, n as:

N = (n −1) × 106

As the conditions of propagation in the atmosphere vary, the interference of radio-wave

propagation is observed. Such interferences are incident with some meteorological parameters

(inversion of temperature, high evaporation and humidity, passing of the cold air over the warm

surface and conversely), (Valm et al., 2010).

The atmospheric radio refractive index depends on air temperature, humidity, atmospheric

pressure and water vapour pressure. Subsequently, meteorological parameters depend on the

height at a point above the ground surface. Variation in any of these meteorological parameters

can make a significant variation on radio-wave propagation, because radio signals can be refracted

over whole signal path (Priestley and Hill, 1985). In the atmosphere, pressure, temperature and

humidity decrease exponentially as height h increases (Falodun and Ajewole, 2006).

According to (Willoughby, 2002), atmosphere has an important feature:- the vertical gradient

of the refractive index, G. The vertical gradient of the refractive index is responsible for bending

of propagation direction of the electromagnetic wave. If the value G is negative, the signal bends

downwards (Guanjun and Shukai, 2000). The characterization of the seasonal variation in fading

and its dependence on meteorological parameters provides the way to improve transmission

performance by better tailoring of performance equipment design and usage to the amount of

fading expected at a given location and time of the year.

In the lowest layer of the atmosphere, the statistics of the vertical gradient of radio refractivity is

an important parameter for the estimation of path clearance and propagation associated effects,

such as surface reflection and multipath fading and distortion on terrestrial line - of – sight links

(ITU-R, 2003). The radio engineer involved in the design of radio communication systems

operating in the above frequency bands (30 MHZ and above), normally subjects long term data

relating to atmospheric refractive index and its properties to statistical analysis in order to be able

to predict these parameters (Aro and Willoughby, 1992).

Among the earliest radio scientist that worked in this field were Bean and Thayer (1959). They

observed that a correlation existed between monthly means of surface refractivity 𝑁𝑠 and monthly

means of refractivity decrease in the first kilometer, ∆𝑁, above the ground. Also, Adebanjo (1977)

determined an empirical relation of the form ∆𝑁 = −25 EXP (0.0022 𝑁𝑠) to indicate the average

change in refractivity between surface and the first kilometer over Nigeria. This relationship was

based on the data for the same stations in Nigeria for which Owolabi and Williams (1970)

computed 𝑁𝑠 values; the ∆𝑁 values were obtained from a world atlas of atmospheric radio

refractivity by Bean et al., (1966). Although the contributions of this scientist to radio science

especially in the African region are invaluable, they could not explore the diurnal trend of

refractivity because of a dearth of atmospheric data, therefore recent efforts (Adedeji and Ajewole,

2008; and Oyedum et al., 2009 and 2010) explore the diurnal trends of surface radio refractivity.

2.1 ATMOSPHERIC PRESSURE

In 1594 Galileo Galilei, obtained the patent for a machine to pump water from a river for the

irrigation of land. The heart of the pump as a syringe Galileo Galilei found that 10 meters was the

limit to which the water would rise in the suction pump, but had no explanation for this explanation

for this phenomenon. Scientists were then devoted to find the cause for this.

In 1644 Evangelista Torricelli (torr) filled a tube 1 meter long hermetically closed at one end, with

mercury and set it vertically with the open end in a basin of mercury. The column of mercury

invariably fell to about760mm, leaving an empty space above its level. Torricelli attributed the

cause of the phenomenon to a force on the surface o0f the earth without knowing where it comes

from. He also concluded that the space on top of the tube is empty, that nothing is in there and

called it a “vacuum”.

In 1648 Blaise Pascal, French physicist and mathematician, heard about the experiment of

Torricelli and was searching for a reason of Galileo’s and Torricelli’s findings. He came to the

conviction that the force, which keeps the column at 760mm, is the weight of the air above. Thus,

on a mountain, the force must be reduced by the weight of the air between the valley and the

mountain. He predicted t6hat the height of the column would decrease which he proved with his

experiments at the mountain Puy de Dome in central France. From the decrease he could calculate

the weight of the air. Pascal called this force, “pressure”, is acting uniformly in all direction.

(Pidwirny, 2006).

In 1820, Almost 200 years later, Joseph Louis Gay-Lussac French physicist and chemist, detected

that the pressure increase of a trap gas at a constant volume is proportional to the temperature.

In 1843 Lucien Vidie, French scientist, invented and built the aneroid barometer, which uses a

spring balance instead of a liquid to measure atmospheric pressure. The spring extension under

pressure is mechanically amplified on an indicator system. Employing the indicator method of

Vidie, Eugene Bourdon (founder of the Bourdon Sedeme Company) patented 1849 the Bourdon

tube pressure gauge for higher pressures. (Pidwirny, 2006).

The first experiment of atmospheric pressure began with a simple experiment performed by

Evangelista Torricelli I n 1643. In this experiment, Torricelli immersed a tube, sealed at one end,

into a container of mercury (see figure 3 below). Atmospheric pressure then forced the mercury

up into the tube to a level that was considerably higher than the mercury in the container. Torricelli

determined from this experiment that the pressure of the atmosphere is approximately 30 inches

or 76 centimeters (one centimeter of mercury is equal to 13.3 mill bars). He also noticed that height

of the mercury varied with changes in outside weather conditions. (Pidwirny, 2006).

In 1648, Blaise Pascal rediscovered that atmospheric pressure decreases with height, and deduces

that there is a vacuum above the atmosphere (Florin to Pascal, 1647).

2.2 TEMPERATURE

It was the beginning of seventeenth century when the thermometer – a temperature measuring

instrument was first developed. Galileo Galilei was credited with the construction of the first

thermometer, although a Dutch Drebbel also made similar instrument independently. The principle

was simple. A bulb containing air with long vertical tube was invented and dipped into a basin of

water or colored liquid. With the change in temperature of the bulb, the gas inside expanded or

contracted, thus changing the level of the liquid column inside the vertical tube. A major drawback

of the instrument was that it was sensitive not only to the variation of temperature, but also to

atmospheric pressure variation.

Successive developments of thermometer came out throughout seventeenth and eighteenth

century. The liquid thermometer was developed during this time. The importance of two fixed

temperatures was felt while graduating the temperature scales. Boiling point of water and melting

point of ice produced two easily available references. But some other references were also tried.

Fahrenheit it developed a thermometer where, I seems, temperature of ice and salt mixtures was

taken as 0” and temperature of human body as 96”. These two formed the reference points, with

which, the temperature of melting ice came as 32” and that of boiling water as 212”. In Celsius

scale, the melting point of ice was chosen as 0” and boiling point of water as 100”. The concept of

kelvin came afterwards, where the absolute temperature of gas was taken as 0” and freezing point

of water was taken as 273” (Version 2 EE IIT, Kharagpur 3).

The earlier devices used to measure the temperature were called thermo-scopes. They consisted of

a glass bulb having a long extending downward into a container of colored water, although Galileo

in 1610 is supposed to have used wine. Some of the air in the bulb was expelled before placing it

in the liquid, causing the liquid to rise into the tube. As the remaining air in the build was heated

and cooled, the level of the tube would vary, reflecting the change in the air temperature. An

engraved scale on the tube allowed for a quantitative measure of the fluctuations. The air in the

bulb is referred to as thermometric medium, i.e. the medium whose property changes with

temperature. (Quinn 1990, Cork 1942).

Robert Hook, Curator of the Royal Society, in 1664 used a red dye in the alcohol. His scale, for

which every degree represented an equal increment of volume equivalent to about 1/500 part of

the volume of the thermometer liquid, needed only one fixed point. He selected the freezing point

of water, by scaling it in this way: hook’s showed that a standard scale could be established for

thermometers of a variety of sizes. Hook’s original thermometer became known as the standard of

Gresham College and was used by the Royal Society until 1709. The first untellable meteorological

records used this scale (Weber. 1950). In 1907, the astronomer Ole Roemer of Copenhagen based

his scale upon two fixed points: snow (or crushed ice) and the boiling point of water and he

recorded the daily temperature at Copenhagen in 1708-1709 with this thermometer. (Quinn 1990).

It was in 1724 that Gabriel Fahrenheit, an instrument of making of Amsterdam, used mercury as

the thermometric liquid. Mercury’s thermal expansion is large and fairly uniform, it does not

adhere to the glass, and it remains a liquid over a wide range of temperatures. Its silvery appearance

makes it easy to read. On this scale, Fahrenheit measured the boiling point of water to be 212.

Later he adjusted the freezing point of water to 32 so that the interval the boiling and the freezing

points of water could be represented by the more rational number 180. Temperatures measured on

this scale are designated as degrees Fahrenheit (ᵒF) (Cork, 1942).

In 1780, J.A. C. Charles, a French physician, showed that for the same increase on temperature,

all gases exhibited the same increase in volume. Because the expansion coefficient of gases is so

very nearly the same, it is possible to establish a temperature scale based on a single fixed point

rather than the two-fixed point scales, such as the Fahrenheit and Celsius scales. This brings us

back to a thermometer that uses a gas as the thermometric medium. (Quinn 1990).

2.3 RELATIVE HUMIDITY

Humidity is the “wetness” of the atmosphere. Relative humidity is the ratio of water vapour present

in the atmosphere as compared to the maximum possible water vapour contents in a given air

volume. Water vapourizes into the atmosphere from many sources such as ocean, rivers, ground

surfaces and through plant transpiration and animal production. 75% of the total air mass of the

atmosphere lies below 10km from the ground (Houghton, 1979). The constituents of the

atmosphere is constant from ground to about 100km and the species are well mixed except water

vapour and ozone (McIntosh and Thom, 1973).

The amount of water that vapourizes into the atmosphere is a function of temperature of the body

exhaling water vapour into the atmosphere and the temperature of the atmosphere because of the

thermal exchange involved.

The water vapour in air (Hess, 1974) could be as high as 5% while about half of the atmosphere

water vapour is concentrated at less than 2km (Houghton, 1979). Water vapour in the stratosphere

comes mainly from conversion of oxidized methane molecules reaching the atmosphere from the

troposphere to water vapour (Hobbe and Deepak, 1981).

OH + CH4 → CH3 + H2O + ∆E

Where ∆E = 15kcalmole

There are ways of loss of water vapour from the stratosphere and the mesosphere and this includes

photo-dissociation (Paiman and Newton, 1969). Water vapour’s presence in the atmosphere is

important to both plants and animals and has an effect on radio wave propagation (Richi, 1979) in

frequency range of 100 kHz to GHz.

Green vegetation humidifies the atmosphere through the process of transpiration. Areas with a lot

of green vegetation are always conducive and refreshing to healthy life. Dry air can cause nose

bleeding in animals.

Relative humidity is obtained from the mass or density relationship

𝑅𝐻 = 𝑀 𝑀𝑑 𝑤ℎ𝑒𝑟𝑒 𝑀 𝑖𝑠 𝑔𝑖𝑣𝑒𝑛 𝑎𝑠 ⁄

M=

𝑀𝑊 𝑀𝐷 = 𝐷𝑊 𝐷𝐷 𝑊ℎ𝑒𝑟𝑒 𝑀𝑑 𝑖𝑠 𝑡ℎ𝑒 𝑠𝑎𝑡𝑢𝑟𝑎𝑡𝑖𝑜𝑛 𝑚𝑖𝑥𝑖𝑛𝑔 𝑟𝑎𝑡𝑖𝑜 (𝑉𝑠𝑤𝑎𝑛𝑎𝑛𝑑ℎ𝑎𝑚, 1981)⁄⁄

If the vapour is coming out of liquid phase, energy in the form of kinetic energy is required to

move through water ‘particle’ to the water surface and an additional energy is required to break

the remainder of the liquid. The thermal energy is

𝑄 = 𝑀𝑆∆𝑇

Where m is the mass of water turned into vapour, s is the specific heat capacity. ∆T is the required

temperature change before vaporization can take place and L is the specific latent heat of

vaporization.

CHAPTER THREE

3.1 Materials and Method

The meteorological parameters (pressure, temperature relative humidity) used to calculate radio

refractivity for Ilorin (University of Ilorin, kwara, State) was measured using the automated

weather station (WH109C ) installed at block 4 up Physics department in the University of Ilorin

premises. The analysis were done for the month of April and May 2106. The hourly variations of

meteorological parameters for each day for five minute (5min) interval for each day were recorded

rainy seasons in Ilorin (University of Ilorin, kwara, State). The average variation of each hour per

day was calculated from the recorded data .The partial pressure

of water e was determined from the equation as follows:

𝑒 = 𝑒𝑠𝐻

Where H is the relative humidity, and 𝑒𝑠 is the

saturation vapour pressure determined by Clausius Clapeyron equation given as:

𝒆𝒔 = 𝟔. 𝟏𝟏𝟐𝟏𝒆𝒙𝒑 [𝟏𝟕.𝟓𝟎𝟐𝒕

(𝟐𝟒𝟎.𝟗𝟕+𝒕)] Where t is measured in Celsius and 𝒆𝒔 is measured in hpa

In relation with the measured meteorological parameters such as the temperature, pressure and

relative humidity radio refractivity was calculated using;

𝑁 =77.6𝑃

𝑇+

3.73 × 105𝑒

𝑇2

Where

P = atmospheric pressure (hPa)

e = water vapour pressure (hPa)

t = absolute temperature (K)

Refractivity of the lower atmosphere (troposphere) is divided into two compositions; the dry and

the wet composition. The dry term contributes a greater percentage, about 70% to the total value

of the refractivity in the atmosphere. The dry term is proportional to the density of the gas

molecules in the atmosphere and changes with their distribution. The dry term of refractivity,

which is fairly stable, can be modeled with an accuracy of about 20% using surface measurements

of pressure, P (hpa) and temperature, T (Kelvin) as:

Ndry = 77.6 𝑃

𝑇

Conversely, the wet term contributes the major variation of refractivity in the atmosphere. Wet

term is due to the polar nature of the water molecules and is given by:

Nwet = 3.73 × 105e/T2

Where e is the water vapor pressure measured in millibar and T is measured in absolute kelvin

(k).

Equation (4) may be employed for the propagation of radio frequencies up to 100GHz

(Willoughby, et al, 2002). The error associated with the application of the above formula is less

than 0.5% (ITU-R, 2003).

3.2 LOCATION AND INSTRUMENTATION SET- UP

The site of the study is located at the premises of University of Ilorin, Kwara State. It has the

coordinate of about (8°32′𝑁𝑎𝑛𝑑 4°34′𝐸). The analysis was done at the beginning of rainy season

of mid (April) and late (MAY) of the year 2016. The instrument for this measurement is the

WH109C professional weather station equipped with the integrated sensor suite (ISS), a battery

source and the wireless console. The console is connected to a computer, through which the stored

data are downloaded. The ISS houses the sensors for pressure, temperature, relative humidity, UV

index and close, solar radiation among others and the sensor interface module (SIM). The SIM

contains electronics that measure and store values of weather variables for transmission to the

console via radio. The fixed measuring method by a high tower is employed for the measurement

with the ISSs positioned on the ground surface and at heights (4m) on the tower for continuous

measurement of the atmospheric pressure, air temperature and relative humidity. The

measurements cover 24 hours each day beginning from 00 hours local time (LT) and for a time

interval of 60 minutes. The data is then transmitted by wireless radio connection to the data logger

attached to the console which is located in-door on the ground. The data are then copied to the

computer laptop for analysis. The error margin of the ISS device for temperature, pressure and

relative humidity are ±0.1℃, ±0.5ℎ𝑝𝑎 𝑎𝑛𝑑 ±

2% 𝑟𝑒𝑠𝑝𝑒𝑐𝑡𝑖𝑣𝑒𝑙𝑦 (www.ea- journals. org).

Fig 3.0: Automated weather station and data logger used

Fig 3.1: Researcher taking the meteorological parameter from automatic weather station

Fig 3.2: The three researcher during the setup of automatic weather station

3.3 PROCEDURE OF ADMINISTRATING THE INSTRUMENT

The data used for the project consist of monthly average values of temperature, relative humidity

and atmospheric pressure. The dataset covers the time period from May 2015.datasets were

obtained from WS1041 professional weather station. Values of refractivity (N) was calculated

from the dataset from the equation given below N = (n-1) × 106 = 77.6 𝑷

𝑻 + 3.73 × 𝟏𝟎5e/T2

CHAPTER FOUR

DATA PRESENTATION AND PRESENTATION OF RESULT

4.1 Hourly Variation of Surface Refractivity

Averages of hourly variations of meteorological parameters for each day were obtained, from the

data collected for rainy season April and May 2016 in Ilorin (University of Ilorin, kwara, state).

The results were used to calculate radio refractivity for each day. In other to achieve this, graphical

comparisons of the measured atmospheric parameters and refractivity were employed and also

with the MATLAB for accurate graphical plots. The plots of diurnal variations of radio refractivity

for rainy season within April and May 2016 are shown in fig 1, 2 and 3 below.

The results are shown in different plots of refractivity against atmospheric parameters during the

season (beginning of rain) April and Late May as represented in the following figures. Figures

4.1.1 – 4.1.3 show the plots of hourly variation in radio surface refractivity, 19/04/2016,

06/05/2016, and 30/05/2016 at the beginning of rainy season (April) and (May).

Fig 4.1.1: shows the hourly Variation of Radio Surface Refractivity for one day (19/04/2016)

Fig 4.1.2: shows the hourly Variation of Radio Surface Refractivity for one day (06/05/2016)

Fig 4.1.3: shows the hourly variation of surface refractivity for one day (30/05/2016)

It was observed in fig 4.1.1 that during the early morning hours, mean refractivity values vary

between 350N-units and 390 N-units but surface refractivity values begin to decrease uniformly

at around (12 – 14hrs). This decrease continues until a minimum of 348 N-units is reached at about

15hrs, before it begins to rise again.

In Fig 4.1.2 it was observed that during early hours, there was decrease in the mean refractivity

which varies between 390 N-units and 385 N-units but surface refractivity values decreases rapidly

at about (6hrs-13hrs) with 355 N-units which decrease uniformly at about (13-15hrs) and later

increase to 380 N-units at about 19hrs before decreases again to 373 N-units at about (19-24hrs).

In Fig 4.1.3 there was sharp increase in refractivity at about (1-2hrs) from 372-387 N-units which

increases uniformly till around 12hrs and decreases gradually from 12hrs to 18hrs with 385 N-

units.

Fig 4.1.4: Comparison of Diurnal Variation of surface refractivity with time from Week1-6 of

April and May 2016

Fig 4.1.4 shows the comparison of diurnal variation of radio refractivity with time at the beginning

of rainy season (April) and late May. In figure 4.1.4, there are high variations through-out the

weeks with the same amplitude variation due to the changes in weather in the lower troposphere

during the rainy season, but the radio refractivity did not vary linearly with time but uniformly.

This may have resulted in the changes in atmospheric weather condition corresponding to this

period which is accompanied by high moisture contents in the troposphere. The high moisture

content resulted in the changes of radio refractivity which attributes to extensive cloud cover and

saturation of atmosphere with large moisture content which increases the humidity in the

troposphere.

Fig 4.1.5: shows the Diurnal plot of relative humidity variation

In contrast, it is clearly noticed in the fig above that relative humidity appears higher during (23-

24hrs) than in the early hour (morning) and observed lower at the afternoon at about (13-15hrs) of

the day.

Fig 4.1.6: Shows the Diurnal plot of Temperature variation.

It was clearly observed in the figure above during the early morning the temperature variation

decrease and tends to be high at a peak around the afternoon and later drops in the evening of the

day.

Fig 4.1.7: shows the hourly variation of surface refractivity for morning of (19/04/2016) between

7am to 2pm.

From the graph above (fig 4.1.7), it shows that the surface refractivity increases as the local time

increases due to an increase in moisture contents which increases humidity while the temperature

decreases. Surface refractivity values ranges from 360 N-units to 390 N-units at about (0hrs-6hrs)

but decreases at about 6hrs -7:30hrs)

Fig 4.1.8: shows the hourly variation of surface refractivity for evening of (19/04/2016) between

4pm to 7pm

Also from fig 4.1.8, surface refractivity increases with local time, there is a sharp increase at about

(0.8hrs-1hrs) and at about (2.25hrs-2.5hrs) before it continues progressively.

Fig 4.1.9: shows the diurnal variation of surface refractivity for first 15-days between (12/04/2016-

26/04/2016)

From fig 4.1.9 above, it shows that surface refractivity values are high (367-380 N-units). Surface

refractivity drops at first hour before it increases sharply 0.37hr-0.4hr) in the morning and zig-zag

variation of surface refractivity occurred, which shows that there is high variation in

meteorological parameters (pressure, temperature and humidity).

Fig 4.2.0: shows the diurnal variation of surface refractivity for last 15-days between

(16/05/2016-30/05/2016)

From fig 4.2.0, which shows the surface refractivity variation for the last 15-days, there was

sharp increase in the early hour at about (0.1hr-0.2hr) with values (379-386.5 N-units) and later

decrease sharply to 0.22hr. High surface refractivity variation was observed from this graph

which predict that meteorological parameters changes with local time

Fig 4.2.1: showing Variation of Surface radio refractivity and Relative humidity with time.

The graph show that there is a good relation between surface radio refractivity and relative

humidity. There graph are similar, which explained that relative humidity varies significantly with

time and it causes the high surface radio refractivity in the atmosphere.

Fig 4.2.2: showing Variation of Surface radio refractivity and Temperature with time.

The graph shows the variation of surface radio refractivity and temperature with time, it was

observed that the temperature graph is opposite the graph of surface radio refractivity, which

explained that increase in temperature reduces the surface radio refractivity of the atmosphere

and there is decrease in relative humidity.

Fig 4.2.3: Shows the plot of Linear Regression on Surface Radio Refractivity and Surface

Relative Humidity.

340

350

360

370

380

390

400

20.5 21 21.5 22 22.5 23 23.5 24 24.5 25

SUR

FAC

E R

AD

IO R

EFR

AC

TIV

ITY

N(N

-un

its)

SURFACE RELATIVE HUMIDITY RH(%)

Fig 4.2.4: Shows the plot of Linear Regression on Surface Radio Refractivity and Surface dew

point temperature.

340

350

360

370

380

390

400

20.5 21 21.5 22 22.5 23 23.5 24 24.5 25

SUR

FAC

E R

AD

IO R

EFR

AC

TIV

ITY

N()

N-u

nit

s

SURFACE DEW POINT TEMPERATURE Td(ᵒC)

Fig 4.2.5: Shows the plot of Linear Regression on Surface Radio Refractivity and Surface

temperature.

From the plots shown in Figure 4.2.2, 4.2.4 and 4.2.5 respectively, the following equation was

derived from the linear regression given below; 𝑁 = 0.7089𝑅𝐻 + 325.71 Where 𝑅2 = 0.9375 (fig

4.2.1), 𝑁 = 11.553𝑇𝑑 + 107.74 Where 𝑅2 = 0.9457 (fig 4.2.2) and N= -3.444T + 478.35

345

350

355

360

365

370

375

380

385

390

395

400

0 5 10 15 20 25 30 35 40

SUR

FAC

E R

AD

IO R

EFR

AC

TIV

ITY

N()

N-u

nit

s

SURFACE TEMPERATURE (ᵒC)

𝒅𝑵

𝒅𝑯= −𝟗𝟕 𝑵 𝒖𝒏𝒊𝒕𝒔/𝒌𝒎 is the average refractive index gradient over Ilorin which was

calculated and found to be -97 N units during the rainy season. This value obtained showed that

the atmosphere was super-refractive during the rainy season.

CHAPTER FIVE

5.0 CONCLUSIONS

The work has shown that the effects of meteorological parameters on the tropospheric radio

refractivity in Ilorin has being attributed to seasonal variations in the troposphere most especially

at the lower part. The variation in weather was observed to be significant during the rainy season

in Ilorin owing to an increase in the troposphere temperature and humidity, and it therefore resulted

to very high refractivity within the period.

In the result obtained for the project it was revealed that surface radio refractivity over Ilorin is

more variable at the beginning of the rainy season, resulting in variation in field strength in the

Very High Frequency (VHF) band in this region.

It was also observed that the beginning of the rainy season exhibited higher refractivity values

ranging from 350 N- units to 393 N- units and also exhibited higher refractivity values from 372

N-units to 397 N-units. Refractivity values varies from 358 N-units to 393 N-units in the early

morning hour and 355 N-units to 397 N-units in the evening. Surface refractivity varies

significantly in both the first 15-days and last 15-days which explained changes in temperature,

pressure, and humidity excellently.

The mean value of surface refractivity obtained in this study is 376 N-units between the periods

of {April 4, 2016- May 30, 2016} and It also shows that monthly mean surface radio refractivity;

N values can be predicted by monthly mean values of humidity with the equation 𝑁 = 0.7089𝑅𝐻

+ 325.71, dew-point temperature with the equation 𝑁 = 11.553𝑇𝑑 + 107.74 and temperature with

the equation N = -3.444+478.35.

The result of refractive index gradients computed showed that the atmosphere over Ilorin was

super-refractive during the rainy season.

The result compare favourably well with the works of Igwe and Adimula (2009) where they

obtained the mean value of surface refractivity for Ilorin to varies between 3 N-units to 378 N-

units.

This high values are attributed to extensive cloud cover and saturation of the atmosphere with

larger amount of water vapour during this period.

5.1 RECOMMENDATION

It is recommended that both the vertical and horizontal extent of this work be undertaken by future

researchers i.e. different point should also be undertaken since it was a single point that was

achieved for this work.

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