determination of the melting layer from meteorological radar data
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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.
vii
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
xiii
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
xvi
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:
7
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.
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