DETERMINATION OF THE MELTING LAYER FROM METEOROLOGICAL

RADAR DATA

OMER ABDEL RAZAG SHARIF ABU BAKER SHARIF

UNIVERSITI TEKNOLOGI MALAYSIA

DETERMINATION OF THE MELTING LAYER FROM METEOROLOGICAL RADAR DATA

2006/2007-I

OMER ABDEL RAZAG SHARIF ABU BAKER SHARIF

√

Dr. NOR HISHAM BIN HJ KHAMIS Industrial Research and Consultancy Centre (IRCC), Khartoum, Sudan. E-Mail: moshakis111@hotmail.com

DECEMBER 2006 DECEMBER 2006

“I hereby declare that I have read this thesis and in

my opinion this thesis is sufficient in terms of scope and

quality for the award of the degree of Master of Engineering (Electrical-

Telecommunication Engineering)”

Signature : ………………………………………...

Name of Supervisor : Dr. NOR HISHAM BIN HJ KHAMIS

Date : ………………………………………...

DETERMINATION OF THE MELTING LAYER FROM METEOROLOGICAL

RADAR DATA

OMER ABDEL RAZAG SHARIF ABU BAKER SHARIF

A project report submitted in partial fulfilment of the

requirements for the award of the degree of

Master of Engineering (Electrical- Telecommunication Engineering)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

DECEMBER 2006

ii

I declare that this thesis entitled “Determination of the Melting Layer from

Meteorological Radar Data“is the result of my own research except as cited in the

references. The thesis has not been accepted for any degree and is not concurrently

submitted in candidature of any other degree.

Signature : ……………………………………………………

Name : OMER ABDEL RAZAG SHARIF ABU BAKER

Date : …………………………………………………….

iii

To

my Beloved Mother, Father, Brothers and Faience.

and to

the Souls of Mohammed Abdel Aziz and Mustafa Hashim

who devoted their lives towards defending Islam and our country.

iv

ACKNOWLEDGMENT

In the name of Allah, Most Gracious, and Most Merciful

Praise be to Almighty Allah (Subhanahu Wa Ta’ala) who gave me the

courage and patience to carry out this work. Pease and blessing of Allah be upon his

last prophet Mohammed (Sallulaho-Alaihe Wassalam) and all his companions

(Sahaba), (Razi-Allaho-Anhum) who devoted their lives towards the prosperity and

spread of Islam.

My deep appreciation and heartfelt gratitude goes to my supervisor, Dr. Nor

Hisham Bin Hj Khamis for his kindness, constant endeavor, guidance and the

numerous moments of attention he devoted through out this work.

I extend my deepest gratitude to my close friend, Eng. Ayman A.A.

Alwarfalli for his encouragement and motivation. A special thanks and deepest

gratitude to my friends, Eng. Abdel razig Saeed Mohammed, Eng. Elmueiz El tayeb

Sulaiman, and Eng. Naji Abdel Gadir Ahmed for providing their workstations to

complete my work.

Acknowledgement is due to my senior colleague and friend Eng. Illiasaak

Ahmad, and my classmate Eng. Sahazati bt. Md. Rozali for translating the abstract to

Bahasa Malaysia. Also, a heartfelt acknowledgement is due to Dr. Abdelwahab

Mohammed Ali, who revised the thesis, for his valuable comments about the thesis

format and the language.

v

A heartfelt gratitude and acknowledgement are due to the Sudanese

community in UTM, Skudai for their kindness, care, valuable advices and

cooperation, which generates a similar environment as what I left.

Sincere friendship is the flavor and spice of life, I owe thanks to my close

friends in Sudan, who offered different kinds of support. Sincere thanks are

extended to my classmates and colleagues in the international student building

(KTC-S46 and S47) at UTM, Skudai.

I would like to extend the acknowledgement to the Industrial Research and

Consultancy Centre (IRCC), Sudan, and all my colleagues there for their continuous

courage and support. Special heartfelt thanks to the Engineering Industries

Department and the Economical Studies Department in IRCC for their cooperation,

patience and unlimited support.

Family support plays a vital role in the success of any individual. I would like

to convey a heartfelt thanks to my parents, brothers, and other family members

including all my uncles, ants and their families; their prayers and encouragement

always helped me take the right step in life. Also special thanks to all neighbors in

Block 11, Alsafiah, Sudan, for their spiritual support and heartiest prayers.

vi

ABSTRACT

The bright band is the enhanced radar echo (reflectivity) associated with the

melting of hydrometeors in stratiform rain. However; incorrect determination of the

bright-band may lead to significant overestimation of precipitation such as rainfall

rate reaching the ground, sometimes by as much as a factor of five, as in the example

for rainfall rate. Radar has the potential to distinguish between different

hydrometeors through the vertical profile of reflectivity by its statistical moments.

The vertical profile can be used to determine the bright band. The main objective of

this project is to determine the boundaries of the melting layer (bright band) based on

the meteorological radar measurements. This determination includes the evaluation

of the rain height and zero degree isotherms height. To achieve this description fully,

the raw radar measurements have been sorted out, filtered, and decoded, plotted and

analyzed. Radar observables have been plotted against the corresponding heights,

and their boundaries have been determined according to the enhancement and

transition of radar parameters. The results give an acceptable correlation with the

international telecommunication union- radio communication sector (ITU-R)

recommendations and a good one with the results that are obtained from the

precipitation radar on-board the tropical rainfall measuring mission (TRMM) satellite

and the characteristics of the melting layer in Singapore, which obtained using S-

band polarization-diversity Doppler radar.

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ABSTRAK

Jalur terang ialah pantulan radar yang ditingkatkan nilainya dan berkait rapat

dengan pencairan pemendakan hujan stratiform. Namun begitu, kesilapan dalam

penentuan kadar gema bagi jalur terang mengakibatkan kesan yang ketara semasa

menentukan kadar pemendakan. Kesilapan anggaran kadang-kala boleh mencecah

sehingga 5 skala-faktor akibat daripada kesilapan penganggaran kadar turun hujan,

contohnya. Radar mempunyai potensi untuk mengklasifikasikan jenis pemendakan

melalui data statistical moments pantulan profil menegak. Oleh yang demikian,

objektif utama dalam projek ini adalah untuk menentukan sempadan-sempadan

lapisan pencairan bagi jalur terang berdasarkan data yang diperolehi daripada radar

meteorologi. Selain daripada itu, penilaian keatas rain height dan zero degree

isotherms height juga dilakukan. Data mentah yang diperolehi dari radar telah

disusun, disaring, dinyahkod, dan seterusnya dianalisa bagi mendapatkan maklumat

yang sebaik mungkin. Data yang telah diproses tadi kemudiannya diplotkan

berlawanan dengan nilai tinggi. Sempadan bagi data-data tersebut ditentukan

mengikut peningkatan dan had transisi radar. Keputusan yang diperolehi adalah

memberangsangkan kerana ianya selari dengan cadangan yang diberikan oleh ITU-

R. Keputusan yang diperolehi juga sama baiknya dengan keputusan yang didapati

melalui radar satelit pemendakan TRMM (Tropical Rainfall Measuring Mission).

Ianya juga bersamaan dengan ciri-ciri pencairan lapisan di Singapura yang diperolehi

melalui radar S-band polarization-diversity Doppler.

viii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT vi

ABSTRAK vii

TABLE OF CONTENTS viii

LIST OF TABLES xi

LIST OF FIGURES xiii

LIST OF SYMBOLS xvi

LIST OF ABBREVIATIONS xix

LIST OF APPENDENCES xx

1 INTRODUCTION 1

1.1 Introduction 1

1.2 Project Background and Problem Statement 2

1.3 Project Objective 5

1.4 Scope of the Project 5

1.5 Project Methodology 6

1.6 Thesis Out line 7

2 METREOLOGICAL RADAR AND

REFLECTIVITY DATA 8

2.1 Introduction 8

2.2 RADAR Review 8

2.2.1 Introduction 8

2.2.2 Target Information Extraction 11

2.3 Meteorological Radar 13

ix

2.3.1 Introduction 13

2.3.2 The Role of the Antenna on

Transmission and Reception 14

2.3.3 Reflection from the Target 16

2.4 Resolution 16

2.5 Meteorological Radar Equation 18

2.5.1 General Radar Equation 18

2.5.2 Radar Equation for Distributed Target 19

2.6 Kluang Radar Station and RAPIC Transmitter 22

2.7 Radar Data Format 25

2.7.1 ASCII Asynchronous Format for Radial

Representation 25

2.7.2 Radar Data Encoding Types 27

2.7.3 Sixteen Level ASCII Encoding 28

2.7.4 Sixteen Level Run Length Encoding 29

2.8 Transmission of Radar Data 30

2.9 Summary 30

3 THE MELTING LAYER, CONCEPT AND

METHODS OF DETECTION 31

3.1 Introduction 31

3.2 The Melting Layer 32

3.2.1 Introduction 32

3.2.2 Meteorological Radar Relationships 33

3.3 Melting Layer Models 35

3.3.1 Introduction 35

3.3.2 ITU-R Models for Propagation in Non-

Ionized Media 36

3.4 Methods for Detecting the Boundaries of the

Melting Layer 38

3.4.1 Introduction 38

3.4.2 Statistical Moments in Multi-Parameter

Radar 39

3.4.2.1 Differential Reflectivity (ZDR) 39

x

3.4.2.2 Linear Depolarization Ratio

(LDR) 40

3.4.2.3 The Co-Polar Correlation ( ρco) 41

3.4.2.4 Differential Phase Shift (ΦDP) 41

3.4.2.5 Ground Clutter Anomalous

Propagation 42

3.5 The Analysis of the Vertical Profile of Radar

Reflectivity 42

3.6 Summary 48

4 METEOROLOGICAL RADAR DATA ANALYSIS 49

4.1 Introduction 49

4.2 Data Preprocessing and Analysis 50

4.2.1 Sorting Radar Data 50

4.2.2 Development of Data Sorting Program

and its Outcomes 59

4.3 Decoding the Meteorological Radar Data 66

4.4 Plotting the Vertical Profiles of Radar

Reflectivity-Height Curve 72

4.5 Determination of the Boundaries of the Melting

Layer 74

4.6 Summary 76

5 RESULTS AND DISCUSSION 78

5.1 Introduction 78

5.2 Heights and Thickness of the Melting Layer 78

5.3 Resolution Range Dependence 85

5.4 Month-to-Month Variability of the Melting

Layer Boundaries 89

5.5 Summary 91

6 CONCLUSIONS AND RECOMMENDATIONS 93

6.1 Summary and Conclusions 93

6.2 Recommendation for Future Work 96

REFERENCES 97

APPENDICES A-D 102-128

xi

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Radar Specifications 22

2.2 15 volumetric elevations angle 26

2.3 16 Volumetric signal strength thresholds and the

corresponding rain rate 28

2.4 The sixteen characters that define absolute levels 29

2.5 The forty-nine characters that define the deviation

encoding 29

4.1 The distribution of radar scans over the elevation angles 51

4.2 The properties of VRP_Kluang1 folder contents 54

4.3 The number of radar images for all elevation angles over

its occurrence period 57

4.4 Distribution of the radar data over its period according to

the corresponding resolution range 62

4.5 Properties of the sorted radar data for 1000m resolution

range 64

4.6 Properties of the sorted radar data for 500m resolution

range 66

5.1 Statistical properties for the heights and thickness of the

melting layer using 500m resolution range 81

5.2 Statistical properties for the heights and thickness of the

melting layer using 1000m resolution range 83

5.3 Comparison between the melting layer heights values in

tropics 83

5.4 Statistical properties for the heights and thickness of the

melting layer using the two resolution ranges, 500m and 89

xii

1000m, in the same period (4th -8th March and 23rd April

1998)

5.5 Monthly variation of the statistical properties for the

heights and thickness of the melting layer (from 2nd

January to 18th June 1998) 91

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Radar simplified block diagram (Edde, 1993) 9

2.2 Spherical coordinates (Edde, 1993) 12

2.3 PPI display of resolution (Edde, 1993) 13

2.4 Monostatic radar observation geometry 15

2.5 RAPIC System 23

2.6 A typical sample of radar intensity scanned by RAPIC

transmitter 27

3.1 Typical radar reflectivity height profile (Thurai et al,

2003) 37

3.2 Reference vertical profile with enhancement region

corresponding to the melting layer (Baldini and

Gorgucci, 2005) 43

3.3 Vertical radar reflectivity profiles for different

meteorological radar parameters (Wilson and Tan,

2001) 45

3.4 VRP data in the bright band region proposed by (Zafar

and Chandrasekar, 2005) 47

4.1 The Meteorological radar data from Kluang radar

station in the first half of 1998 50

4.2 Distribution of radar images over RHI scans 51

4.3 All radar images that captured using 0.5° EA copied to

folder EA 0.5 52

4.4 Radar images from 2nd to 9th January copied to Kluang1

EA_0.5 folder 53

4.5 The meteorological radar data for all RHI scans 53

xiv

according to the time series of occurrence

4.6 Contents of VRP_Kluang1 folder 54

4.7 The flowchart of sorting the radar data 61

4.8 The sorted meteorological radar data for 1000m range:

(a) the date folders (parent folders), (b) radar radials in

the first day (00298) (children folders), and (c) the radar

images which are captured in 04:22 gmt for all the

elevation angles 64

4.9 The flow chart of the developed decoding algorithm for

the radar data 69

4.10 The flow chart of the decoding algorithm provided by

Australian Meteorological Bureau 70

4.11 Sample of decoded radar data (a) The decoded radar

data according to the AZ, (b) Plot of the decoded data in

term of reflectivity against radar range and AZ 71

4.12 Combination of the decoded radar data for the 15 EAs

after being sorted according to the radial angles and

assembled in a three dimensions matrix 73

4.13 Determination of the vertical height of the 15 decoded

points according to the elevation angle and the scan

range 73

4.14 Some samples of the vertical profile of radar reflectivity

curve 75

4.15 The flow chart of determination the boundaries of the

melting layer 77

5.1 Spread Plots of the Boundaries of the Melting Layer

using 1000m Resolution Range: (a) h0-dBZ, (b) hR-

dBZ, and (c) BBH-dBZ 80

5.2 Histograms of the melting layer boundaries using 500m

resolution range: (a) Histogram of h0, (b) Histogram of

hR, (c) Histogram of BBH, and (d) Histogram of BBth 81

5.3 Spread plots of the boundaries of the melting layer

using 1000m resolution range: (a) h0-dBZ, (b) hR-dBZ, 82

xv

and (c) BBH-dBZ

5.4 Histograms of the melting layer boundaries using

1000m resolution range: (a) Histogram of h0, (b)

Histogram of hR, (c) Histogram of BBH, and (d)

Histogram of BBth 83

5.5 Height of clouds over Klang valley(Malaysia) on 9th

March 2006 85

5.6 The spread plots of boundaries of the melting layer

using the two resolution ranges (RRs): (a) h0-dBZ for

500m RR, (b) h0-dBZ for 1000m RR, (c) hR-dBZ for

500 RR, (d) hR-dBZ for 1000 RR, (e) BBH-dBZ for

500m RR, and (f) BBH-dBZ for 1000m RR 87

5.7 Histograms of boundaries of the melting layer using the

two resolution ranges (RRs): (a) Histogram of h0 for

500m RR, (b) Histogram of h0 for 1000m RR (c)

Histogram of hR for 500m RR, (d) Histogram of hR for

1000m RR, (e) Histogram of BBH for 500m RR, (f)

Histogram of BBH for 1000m RR and (g) Histogram of

BBth for 500m RR, and (h) Histogram of BBth for

1000m RR 88

5.8 Month-to-Month variability for (a) h0, (b) hR, (c) BBH,

and (d) BBth 90

D.1 Spread plots of the boundaries of the melting layer

using 500m resolution range: (a) h0- hR, (b) h0- BBH (c)

h0- BBth (d)hR - BBH, (e) hR – BBth and (f) BBth- BBH 129

D.2 Spread plots of the boundaries of the melting layer

using 1000m resolution range: (a) h0- hR, (b) h0- BBH

(c) h0- BBth (d)hR - BBH, (e) hR – BBth and (f) BBth-

BBH 130

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LIST OF SYMBOLS

A Area (m2)

A Total Attenuation (in dB)

Ag Geometric area

Aeff Effective area (m2)

ASin Inner average slope

ASout Outer average slope

BBH Radar bright-band height (km)

BBth Bright band thickness (km)

CR Radar calibration constant

c Velocity of propagation (m/sec)

D Diameter (m), size of particles

Do Outer diameter (m)

Di Inner diameter (m)

dBZ dB Z= 10 log10 Z

e Relative dielectric constant

em Dielectric constant of the medium

ein Dielectric constant of the inclusions or embedded particles

FH Freezing height (km)

f Fraction of the total particle volume

f Frequency (Hz)

Gt(r) Gain of the transmitted antenna in direction r

Gr(r) Gain of the received antenna in direction r

H (t-τ) Impulse response of the radar receiver

h Length of square-wave pulse in Radar

hB Bottom border of bright band

hbot Bright band region bottom height (km)

xvii

hpeak Height of peak of bright band reflectivity

hR Rain height (km)

hT Top border of bright band

htop Bright band region top height (km)

h0 0°C isotherm height, peak of reflectivity

L Losses of microwave measurement element

LDR. Linear depolarization ratio

N Concentration of particles in certain size

N (D) The drop size distribution (DSD)

n Complex index of refraction

P1(r) Power transmitted in direction r (W)

P2(r) Power transmitted by omni-directional antenna in direction r (W)

Pt Transmitted power (W)

Pr Received power (W)

R, r Range, distance or radius (m)

Tx Transmitter

V Resolution volume (m3)

W Power density (W/m2)

Z Effective reflectivity factor (mm6/m3)

ZDR Differential reflectivity

ZH Reflectivity measured at horizontal polarization

ZV Reflectivity measured at vertical polarization

Ze Effective radar reflectivity factor (mm6/m3)

Zpeak Peak of bright band reflectivity

Zrain Reflectivity of rain

Zsnow Reflectivity of snow

Ω Antenna solid angle

ΦDP Differential phase shift

η Radar reflectivity (m2 m-3)

λ Wavelength (m)

τ Pulse duration (second)

σ Effective area of the radar target (m2)

σH Backscatter cross section for horizontal polarization

xviii

σV Backscatter cross section for vertical polarization

γg Specific attenuation for atmospheric gases (dB/km)

γc Specific attenuation for clouds (dB/km)

γp Specific attenuation for precipitation (dB/km)

φ Latitude of the earth-station location

ρco Co-polar correlation

δco Scattering differential phase

xix

LIST OF ABBREVIATIONS

ASCII American Standard Code for Information Interchange

AZ Azimuth angle (degree)

BB Bright Band

CW Continuous wave

DSD Drop Size Distributions

EA Elevation angle

EM Electromagnetic

ISO International Standard Organization

ITU-R International telecommunication union – Radio communication

sector

JDN Julian Day Number

LOS Line-of-site

PPI Plan position indicator

PE Permanent Echo

RADAR Radio Detection And Ranging

RCS Radar Cross Section

RHI Range Height Indicator

RIU Radar Interface Unit

RR Resolution Range

SNR Signal to Nose ratio

TRMM-PR Tropical Rainfall Measuring Mission-Precipitations Radar

UK United Kingdom

UTM Universiti Teknologi Malaysia

VPR Vertical profile of radar reflectivity

VRP Vertical reflectivity profiles

xx

LIST OF APPENDICES

APPENDIX TITLE PAGE

A A MATLAB PROGRAM FOR SORTING THE

RADAR DATA

102

B A MATLAB PROGRAM FOR PLOTTING

THE VERTICAL PROFILE OF THE RADAR

REFLECTIVITY

106

C A PART OF MATLAB PROGRAM FOR

DETECTING THE RAIN EVENT AND

DETERMINE THE BOUNDARIES OF THE

MELTING LAYER

122

D SCATTER PLOTS FOR THE HEIGHTS AND

THICKNESS OF THE MELTING LAYER FOR

THE WHOLE METEOROLOGICAL RADAR

DATA WITH 500MAND 1000M

RESOLUTION RANGE AND THEIR

REGRESSION BEST–FIT LINES

128

CHAPTER 1

INTRODUCTION

1.1 Introduction

Satellite communications systems become an important segment of the global

telecommunication infrastructure. This includes an integration of number of

applications and services, which use satellites to relay radio transmissions between

earth terminals. These services had traditionally been available via terrestrial

networks and radio broadcastings.

With the rapid growth of the information technology there is an increasing

demand for broadband satellite services, which will provide reliable transmission of

information. Multi-media applications including data and video require large

bandwidth and low error rates for satisfactory performance. This demand will

exceed the present services existence today. Furthermore, there will be increasing

problems of finding the required frequency spectrum to provide the bandwidth for

broadband services, which has brought saturation to the conventional frequency

bands allocated for satellite services, namely L (1/2 GHz), S (2/4 GHz), and C (4/6

GHz).

New and demanding satellite applications evolved has led to utilize and

exploit higher frequencies bands such as Ka-band (20/30 GHz) and above. Spectrum

at Ka-band (20/30 GHz) or higher frequencies band has great importance for

broadband services. This is because of its relatively unused spectrum with no

2

congestion problem, which offers much greater bandwidths, frequency reuse

capability than the current spectrum at Ku-band (11/12 GHz), and smaller

component sizes.

1.2 Project Background and Problem Statement

The use of higher and higher frequencies in telecommunication systems

requires the investigation of the effects of troposphere on electromagnetic wave

propagation, and particular attention must be paid to the attenuation induced by

raindrops and other hydrometeors along the radio path (Capsoni et al, 2003).

Rain affects the design of any communication or remote sensing system that

relies on the propagation of electromagnetic waves thorough the lowest 10 km of

Earth’s atmosphere at frequencies above 1GHz. Communication systems may

experience loss of signal due to the attenuation caused by rain on a radio link and

might be temporarily unavailable for use. The problem for system designers is the

prediction or forecast the effects of rain on communication system located anywhere

on or above the surface of Earth (Crane, 1996).

The direct measurements approach to investigate the rain effect and its

parameters is, in most cases, not feasible or convenient because of the cost and time

to collect statistically meaningful data and the difficulty to extrapolate the results to

other sites. Therefore, nowadays, the indirect measurement technique has become

widely used. In this respect, there is a growing interest on radar data; the main

reason is the ability of this instrument to detect with great spatial detail precipitation

over a large area, in real time, and with a single installation. Radar data can be used,

in principle, to evaluate through simulations, propagation impairments due to

hydrometeors for any length of ground or satellite radio paths, any kind and

complexity of the radio system and for any frequency. The drawback is that radar

reflectivity (Z), which is the basic measure of the meteorological target, cannot be

directly used; its conversion to rain intensity (or attenuation) is not unique,

depending mostly on Drop Size Distributions (DSD). Hence, the need of a

3

“calibration” that multi-parameter radar can carry out, in some way, using the set of

independent measurements on the state of precipitation they perform, while single

parameter radar cannot (Capsoni et al, 2003).

The enhancement in radar reflectivity caused by melting snowflakes below

the 0°C isotherm is known as the “bright-band”. It is due to changes in size, fall

speed and phase during the melting process. If unrecognized, the bright-band can

lead to significant overestimation of precipitation reaching the ground, sometimes by

as much as a factor of 5 (Tan and Goddard, 1995).

Although the qualitative explanation of the reflectivity enhancement causing

the bright band has been made by Ryde (1946), still there is no consensus after more

than 60 years on a quantitative assessment because the bright band is usually more

intense than predicted. Earlier quantitative estimates by Austin and Bemis (1950);

Wexler (1955); Wexler and Atlas (1956); and Lhermitte and Atlas (1963) as well as

the models of Ekpenyong and Srivastava (1970) either confirmed this observation or

attempted to explain the differences either through shape effects (non-sphericity of

snowflakes and melting snowflakes, Atlas et al.(1953) or by growth of precipitation

through condensation and aggregation at the top of the melting layer followed by

breakup below. This aggregation-breakup combination appeared essential in all

cases to explain the bright band intensity and several in-situ or aircraft measurements

were attempted to verify this claim. However, there is still debate as to whether this

effect is important (Stewart et al. 1984; Yokoyama et al., 1985; Willis and

Heymsfield, 1989) or negligible (Du Toit 1967; Ohtake 1969). Recent models of

Dissanayake and McEwan (1978), Klaassen (1988), and Hardaker et al. (1991) either

obtain correct reflectivity enhancement or overestimate the bright band intensity by

considering the bright band enhancement to be caused by the melting of low-density

snowflakes alone.

The lack of agreement between model results and observations is also

exacerbated by the fact that there are no extensive measurement records of the bright

band. Most comparisons of models and observations are too often based on one or

few events or even simply on the first published bright band measurement made with

a Doppler radar (Lhermitte and Atlas, 1963). Given the large number of factors that

4

may influence the bright band shape such as snowflake sizes and shapes, temperature

profile, and vertical air velocity, it is not surprising to have so many, often

contradictory, explanations of the bright band phenomenon (Fabry at el., 1994).

The lack of knowledge on the detailed physics of the melting layer has some

practical consequences in hydrology and microwave communication. In microwave

communication, the enhanced reflectivity of the bright band results in enhanced

scattering and greater signal extinction. Scattering causes interference between

microwave links while extinction disrupts communications. As current microwave

frequencies are becoming crowded, new bands will have to be used and a good

quantification of bright band effects becomes necessary to estimate the reliability of

these new frequencies. Knowledge of attenuation by the melting layer will also be

crucial in order to properly estimate rainfall using short wavelength space-borne

radars (Fabry at el., 1994).

The estimated rain rate from ZH,V is undoubtedly overestimated. It is

necessary to correct for the effect of the bright-band on radar measurements when

attempting to interpret estimates of rain rate from radar data. The critical step is to

detect the height where the melting process happens, which means the height of

bright-band (Tan and Goddard, 1995).

Finally, the bright band phenomenon is a challenge to the knowledge of

precipitation physics and scattering theory. The inability to explain it quantitatively

is a proof that our understanding of these topics is incomplete and additional efforts

must be invested to quantify the mechanisms causing the bright band.

Long term measurements of the bright band will allow us to derive the

dependence of bright band characteristics on precipitation type and intensity that

should help to quantify the contribution of the various causes to the bright band

signature. Averages over long records are insensitive to the peculiarities of a given

event, such as contamination by horizontal advection, and emphasize the

characteristics that are persistent and related to the physics of snow melting.

Although no upper air microphysical observations can be made over such a long

5

period, several hypotheses can be tested using the average reflectivity signature in

and around the melting layer.

Data collected in the first half of 1998 using meteorological S-band radar

located in Kluang (Malaysia) are used to compute average profiles of radar

reflectivity in and surrounding the melting layer in an attempt to determine its

boundaries.

From the above discussion, it is clear any obtained data about the rainfall rate

cannot be directly interpreted. It is rather important to predetermine the boundaries

of the melting layer in order to conduct a valid as well as accurate estimation of the

rain rate.

1.3 Project Objective

The main objective of this project is to determine the boundaries of the

melting layer (bright band) based on the meteorological radar measurements. This

determination includes the evaluation of the rain height (hR), zero degree Celsius

isotherm height (h0), melting layer or bright band height (BBH) and its thickness

(BBth).

1.4 Scope of the Project

The scope of this project includes:

• Instrument and Location: Meteorological S-band radar belongs to the

Meteorological Department of Malaysia, which is located in Kluang

(Latitude=2.02°, Longitude=103.320° and height=88.1 m above MSL).

6

• Duration: The used data covers 116 days collected over the period from 2nd

January to 18th June 1998 for 285,231 scans (1.26 GB on disk) with 15

elevation angles of 0.5°, 1.2° 1.9°, 2.7°, 3.5°, 4.6°, 6.0°, 7.5°, 9.2°, 11.0°,

13.0°, 16.0°, 20.0°, 25.0°, and 32.0°

• Resolution Range: Two types of radar resolution ranges of 500m and 1000m

were used interchangeably and simultaneously.

• Development of programs to sort out, filter, decode the radar data and plot

the vertical profile of radar reflectivity from the decoded data over the radar

ranges using MATLAB platform (version 7.04 release14).

• Determination the melting layer boundaries according to the plotted profile.

These boundaries include the rain height (hR), zero degree Celsius isotherm

height (h0), melting layer or bright band height (BBH) and its thickness

(BBth).

1.5 Project Methodology

To carry out this project, the following methodology is designed:

• Build up of the vertical reflectivity profile (VRP) based on radar data,

which includes the following tasks:

o Preprocessing tasks, which include sorting out and filtering the

meteorological radar data.

o Decoding the radar data, and calculation of its reflectivity

intensity in decibel (dBZ) for the full range of Azimuth for all the

15elevation angles.

o Plot the reflectivity versus height curves.

• Determination of the boundaries of bright band according to:

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o Curvature of reflectivity versus height curve.

o Increasing and Decreasing of reflectivity.

o Maximum reflectivity.

• Comparison the results with ITU-R model and other models in tropical

regions for validation

1.6 Thesis Out line

Chapter one concerns with the introduction of the study in hand, which starts

with brief introduction, and continues stating the problem, the objective, the scope of

the study and finally methods employed to achieve the goals set forth. Chapter two,

which is the first chapter of the literature review, presents the RADAR principles and

characteristics, by focusing on meteorological radar, which its data is used in this

project. Chapter three shows the concept of the melting layer and its properties. In

this chapter, different procedures of detecting and determining the boundaries of the

melting layer are explored. Chapter four explains the execution of the project by

driven its wheel and handle the analysis of the meteorological data. Chapter five

presents and discuses the findings of the analytical procedures employed. The results

were interpreted and compared with the ITU-R recommendations and other findings

in the tropical region to measure the validity of the obtained results. Chapter six

summarizes and emphasizes the obtained results and the contribution of the study.

This chapter also proposes the future work that can be done for more accurate

determination of the boundaries of the bright band as well as better understanding of

the melting process and its characteristics.