DWR Lecture Series IIGST modified iigst.

Dwr lecture series iigst

1. An Introduction to
Doppler Weather Radar
& Study of
Severe Weather Events
(Lecture Series)

Dr. Devendra PradhanDr. Devendra Pradhan
Ex- Additional DG, IMDEx- Additional DG, IMD

2. Topics to be covered
Radar Principle
Types of Radars:-
Analog, Digital, Non-Doppler and Doppler
Weather Radars (Single and Dual polarization
systems)
 Range limitation of Weather Radars due to
the Earth curvature
Pulse Radar
Selection of Wavelengths in Weather Radars

3. RADAR
An acronym for
Radio
Detection
And
Ranging

4. 
Introduction
It is an Electronic Device for detecting and
locating a target by means of radio waves
generally known as “ Microwaves”.(The
waves used in Mobile, satellite, Microwave
Ovens)
The Electromagnetic energy “Reflected”
from the target is analyzed by the receiver to
determine the characteristics of the target.

5. Principle of Weather Radar
EM waves Water Drop

6. Classification of Radars

7. PRIMARY RADAR
A primary radar transmits high-frequency signals
which are reflected by passive targets. Resulting
echoes are received and evaluated. Unlike secondary
radars, primary radars receive self-emitted signals
as echoes.
SECONDARY RADAR
Secondary radars receive signals from active targets. It
could be a response from an aircraft transponder or signals
transmitted by radiosondes etc.

8. Defence RADAR
Such radars are primarily used for Defence
purposes to detect the enemy planes, Tracking the
trajectory of the missiles over a long range.
Weather RADAR
Such radars are used for detection and monitoring
the weather events such as Thunderstorms,
Hailstorms, Cyclones, Tornadoes, Heavy Rainfall etc.
Hydrometeors (Water drops, snow, hail etc) are the
back scatterers of EM waves.

9. Analog Weather RADAR
Such radars were used till 1980. These radars
were analog systems with “Cathode Ray Tubes”
to visualize the echoes of the transmitted signals
from the transmitting antenna after striking from a
target.
Digital Weather RADAR
These radars were an advance stage over Analog
radars where data storage was possible to archive the
data related to an event.

10. Non Doppler
&
Doppler Radars

11. Non-Doppler Radars
Provide only the amplitude of returned echoes
from Weather objects but does not provide the
information about their movement speed or direction.
Doppler Weather Radar (DWR)
Provides information about the velocity of movement
(Speed and Direction) in addition to the amplitude
of the returned echoes.

13. Effect of Earth Curvature
over the range of observation
of Radar

14. Fig 1

15. PULSE RADAR
 Pulse radar is a primary radar which transmits high-frequency signals of high
power for a very small duration (1-2 micro seconds).
 After this a longer break occurs during which echoes can be received after
reflection from a target before the transmission of another signal.
 Direction, distance and height of the target can be determined from the
antenna positions and propagation time of the pulse-signal.

16. Principle of Pulsed Radar

17. Band Frequency Wavelength Applications
VHF 30-300 MHz 10-1 m Wind Profilers
UHF 300-1000 MHz 1 -0.3 m Wind Profilers
L 1-2 GHz 30-15 cm
S 2-4 GHz 15-8 cm Clouds study, heavy
rainfall and Cyclone
prediction
C 4-8 GHz 8-4 cm Clouds study and
aviation
X 8-12 GHz 4-2.5 cm Clouds prediction
Ku 12-18 GHz 2.5-1.7 cm Satellite borne Radars
K 18-27 GHz 1.7-1.2 cm ----------do-----------
Ka 27-40 GHz 1.2 -0.75 cm ----------do-----------
mm 40-300 GHZ 0.75-1 mm Microwave rain radars
Frequency Bands used in the Meteorological applications

18. Attenuation(Loss)
V/S
Frequency

19. Fig 2
Fig 3
Fig 4
X Band
C Band
S Band

20. Advantages of Doppler Weather Radar over
Conventional Analog Radars
Conventional Radar Doppler Weather Radar
 Qualitative observations Quantitative observations
 Analog data Digital data
 No computer archive Total computer archive
 Only reflectivity data Reflectivity & velocity data
 PPI & RHI products only Many derived products
 Manual system Automatic system
 No software processing Complete software
processing of the raw data

 No auto warning Auto warning system

21. What is Doppler Weather Radar?
It is a state of art weather radar which provides:-
• Rainfall rate & total rainfall associated to a cloud, Intensity of cyclone, speed of winds, direction of movement of a system.
• Direction and speed of movement of the thunderstorms, tornadoes & cyclone.
• Estimation of wind speed accompanied with a cyclone, expected storm surge height and potential of destruction.

22. What for Doppler Weather Radar?
• Tracking of cyclones, Prediction of thunderstorms,
Hailstorms, Tornadoes.
• Prediction of landfall place and landfall time of a
cyclone with a very high accuracy.
•Prediction of heavy rainfall, arrival of
thunderstorm over a place, flood forecast and
detection of tornado.
•Estimation of the winds associated to a cyclone
and thunderstorms.
• Study of structural analysis of Cyclones,
Thunderstorms, Hailstorms, Tornado etc.

23. Information from Doppler Weather Radar
•Vertical extent and “Three Dimensional Structure” of
clouds.
•Damage potential of the severe weather phenomena.
•Winds associated with the cyclone.
•Precise prediction of the movement of the
thunderstorm.
•Quantitative rainfall
• Estimation of Gusty winds associated with
thunderstorm .
• Detection of Hailstorms, tornadoes etc.

24. What is the level of confidence in Cyclone
forecasting using Doppler radar?
90 % accuracy in landfall time and location at
least 8-12 hrs before the landfall.
 80% accuracy 12-16 hrs before the landfall.
 80% accuracy in the wind speed measurement.
 80 % accuracy in estimation of heavy rainfall.

25. Why the casualties occur when DWR forecasting
is so accurate?
Lack of confidence in the people on IMD’s forecast.
 Lack of communication channels between disaster
management authorities and the people.
 Delay in communication at local level.
 People do not want to move away from their place
of stay due to poverty.
 Networking of DWRs is required by IMD(under
process)

26. Limitations of the Radar
Requires more sophisticated interpretation of radar
return in terms of atmospheric structure and processes
than that is required in conventional radars.
Contoured displays of radial velocity do not show motion
direct across the beam called the “Transverse” motion.
Due to beam widening and increasing height above the
earth with increasing range, meteorological targets
smaller than the resolution volume can not be studied.
 SRI (Surface Rainfall Intensity) is measured at a height
above the ground and hence it may not be the same as
measured by the surface rain guages.

27. Doppler Weather Radar in Cyclone Monitoring

28. Monsoon
Forecast
Marine
Forecast
Tourism
Forecast
Aviation
Forecast
Cyclone
Forecast
Agriculture
Forecast
Fog Forecast
Forecast for
Railways
Aviation
Forecast
Heavy Rainfall
Forecast
Nowcast

30. Decibel (dB)
Power is usually expressed in Watts but the Power Gain is
expressed in dB as
P
ref
P
out


Power Gain in dB = 10 log
10
(P
out
/ P
ref
)
If P
out
= 2 x P
ref
then,
Power Gain in dB = 10 log
10
2 = 3.03 ≈ 3
Therefore, 3 dB power gain is equivalent to twice the reference
power.
Similarly when P
out
= 10 x P
ref
then
Power Gain in dB = 10 log
10
10 = 10
10 dB power Gain is equivalent to ten times the reference
power.
Amplifier

32. dBm
When Reference power is 1 mW then power is
expressed in dBm.
Power in dBm = 10 log
10
(

P
out
/ 1mw )
When P
out = 1 mW, Power in dBm is 0.
Therefore, 0 dBm = 1 mW, 3 dBm = 2 mW
6 dBm = 4 mW, 9 dBm = 8 mW
10 dBm = 10 mW= 10
1
mW
20 dBm = 100 mW= 10
2
mW
30 dBm = 1000 mW= 10
3
mW = 1W

33. 40 dBm = 10 W
50 dBm = 100 W =10
2
W
60 dBm = 1000 W = 10
3
W =1 KW
Since 0 dBm = 1 mW
-3 dBm = (½) mW
-6 dBm = (1/4) mW
-9 dBm = (1/8) mW
-10 dBm = (1/10) mW =10
-1
mW
-20 dBm = (1/100) mW =10
-2
mW
-100 dBm = 10
-10
mW

34. dBw
When P
ref
= 1 W
then power is expressed in dBw.
Power in dBw = 10 log
10 (
P
out / 1w )
When P
out = 1 W, Power in dBw is 0.
Therefore, 0 dBw = 1 W, 3 dBw = 2 W
6 dBw = 4 W, 9 dBw = 8 W
10 dBw = 10 W= 10
1
W
20 dBw = 100 W= 10
2
W
30 dBw = 1000 W= 10
3
W = 1KW

36. Since 30 dBm = 1w and 0 dBw= 1W
Therefore, 30 dBm=0 dBw =1 W
40 dBm=10 W=10 dBw
Power in dBw = Power in dBm+30 dBm
60 dBW= 60dBm+30 dBm= 90 dBm

37. Exercise
1.Define dBm in terms of power
2.Convert 86 dBm in KW
3.Convert -40 dBm in Watts
4.Convert -107 dbm in Watts
5.Convert 60 dbm in dBW
6.Wavelengths corresponding to 9375 MHz,
5.6 GHz and 3 GHz? What are these bands?

38. What are
Z
&
dBZ?

39. Z-R Relation
The Rainfall Rate can be evaluated from the relation.

Z = a R
b
Where a and b are empirical constants.
When a= 200 and b = 1.6
The relation is known as “Marshal Palmer” Relation.
10 log
10
Z= 10log
10
a + 10 b log
10
R
10 Log
10
Z- 10 log
10
a = 10 b log
10
R
Log
10
R = (1/10b)( dBZ- 10 log
10
a)
R = Anti log
10
{ (dBz-23)/16}

40. Types of scattering
Rayleigh Scattering
 Mie Scattering

41. Rayleigh Scattering
When the size of the target is small compared to the
wavelength of the radar, the back scattering energy is
inversely proportional to the fourth power of the
wavelength. This is known as Rayleigh Scattering.
The back scattering cross sectional area (σ) is directly
proportional to the sixth power of the diameter(D) and the
expression for σ is given by
σ = { π
5
/ λ
4
} |K|
2
D
6
(1.1)
where K is a parameter related to the complex index of
refraction (m)of the substance and is given by
K = (m
2
-1)/( m
2
+2) (1.2)
The complex index of refraction is also expressed as
m = n- ik (1.3)

42. Mie Scattering
 When the size of the target is comparable to the
wavelength of the Radar, the scattering is termed
as Mie Scattering.

43. Doppler Principle in Radar
Doppler discovered that a moving object shifts the
frequency of sound which is proportional to speed of
movement.
 Exactly the same thing happens with Electromagnetic
Radiations.
The radar is stationary and target is moving. Thus the
back scattered radiation from a moving object will have
it’s frequency shifted in proportion to the speed of
movement of object.

44. Thus by measuring the phase difference between
the transmitted signal and received signal, one
can estimate the velocity of the object towards or
away from the radar.
The Doppler radar utilizes the phase property of
electromagnetic radiation for estimation of speed
of the object.
 The amplitude is utilized to detect and estimate
the power received to detect and estimate the
power received from the object, as done in
conventional (Non-Doppler) radar.

45. Volume Scan strategy

47. Principle of Doppler Weather radar
Doppler Weather Radar is based on “Doppler
Effect” in electromagnetic waves.
If there is a relative motion between the source
of the electromagnetic waves and the target then
the reflected signal from the target gets a change
in the frequency or phase as compared to the
transmitted signal.
This change in the frequency is known as
Doppler Shift and is directly proportional to the
relative velocity between target and the source of
electromagnetic waves.

48. *
*
* *r
r

49. Maximum Unambiguous Velocity
The maximum velocity a Doppler radar can detect
correctly or unambiguously is called the maximum
Ambiguous Velocity.
 PRF is the pulse repetition frequency of the radar. Thus,
the maximum unambiguous velocity detectable by a
Doppler radar is
V
max = PRF λ / 4

50. Maximum Unambiguous Range
The electromagnetic radiation travels at the speed of light.
The time it takes for a signal to go out and back from a
target is
T = 2r/c
 c is the speed of light,
 r is the range
 t is the time.
 The “2” accounts for the distance out and back from the
target.

51. The time T between pulses is also termed as Pulse
Recurrence Time (PRT) and given by the relation
T = 1 / PRF
PRF – Pulse Repetition Frequency
Now ,given T ,we can determine the maximum range a
radar signal can travel and return before the next pulses
is sent out. This is simply
r
max = c T / 2
r
max = c / ( 2.PRF)

52. Doppler Dilemma
Maximum unambiguous velocity
V
max = PRF λ / 4
Maximum unambiguous range
r
max = c / ( 2.PRF)
By solving both equations for PRF and equating
them, we find that
V
max r
max = c. λ / 8
This form what has been called the” Doppler Dilemma”.
The Doppler Dilemma: There is no single PRF that
maximizes both R
max
and V
max

53. Base Products
Reflectivity (Z) : A measure of size and number
of droplets in sample volume.
Mean Radial Velocity (V) : A measure of mean
wind towards or away from radar in sample
volume.
Spectrum width (W) : A measure of variability
of radial velocity I.e. turbulence in sample
volume.

54. Radar Reflectivity Factor (Z) :
This product is a measure of the
precipitation in the sample volume of a
cloud system.
 The quantitative estimate of the
precipitation contents, rainfall rate and
other features of the system may be
understood from this product.
Radar Reflectivity factor (Z) expressed in
the units of mm
6
/ m
3.

55. Usually the range of reflectivity factor varies from
a very small value of the order of 10
-2
to a very
large value in the order 10
8
and therefore it is
convenient to express Z in the logarithmic scale
denoted as dBZ given by
dBZ = 10 log
10 {Z /(mm
6
/m
3
)}

57. Radial Velocity (V)
This product is a measurement of mean wind
velocity of the system towards or away from radar
using Doppler Principle.
 As the radar is able to measure only the radial
component of the wind velocity (along the radar
beam), the velocity is referred as radial velocity.

58. 
The radial velocity towards the radar will be
taken as negative and will represent the actual
wind velocity if the system is approaching the
radar along the radar beam.
On the other hand, the radial velocity is taken
as positive if the radial velocity is measured
away from the radar in the outwards direction.
The radial velocity will be zero if the wind is in
the perpendicular direction of the radar beam.

61. Spectrum Width
This product shows the dispersion of the velocities of
the individual particles with reference to the mean
velocity of the system in the form of a spectrum of
velocities and is a measure of turbulence in the
system.
The unit of measurement is m/s and is shown by the
pseudo colors for the presentation in the Doppler
Weather Radar images.

62. Beam width
•The angle between the two directions on either side
of the maximum where the power density is half of
that in the direction of the maximum is called the
beam width of the antenna. It is measured in both
the directions i.e. horizontal beam width (θ) and
vertical beam width (Φ).In the Doppler Weather
radar use under study the horizontal and vertical
beam widths are each of 1
0
.

63. Beam width

64. •The beam width depends upon the wavelength of the radar (λ)
and size of the antenna (D) and given by the relation
Φ = 1.22 λ/ D (Radians)
Φ = 70 λ/ D (Degrees)
1
0
= 70 λ/ D
D= 70 λ
For S band, λ=10 cm , D= 700 cm= 7 m
For C band, λ=5 cm, D=3.5 m, X Band λ= 3 cm D =2.1 m

65. The relation shows that beam width is directly proportional
to the wavelength of the radar and inversely proportional to
the diameter of the antenna.
In case of S-Band radar, λ = 10 cm, Φ = 1
0
therefore,
diameter of the antenna is about 8.3 m. To get more
resolution and accurate estimations, it is desired to have
narrow beam widths but that puts a limitation on the size of
the antenna and therefore a compromise is preferred in the
beam widths and the application of the radar.
For example, in space borne radars, smaller size antenna is
desired and therefore, beam widths of the order of 2-3 deg
are also used.

66. Severe Weather Events

Thunderstorm
Hailstorm
Cyclone
Tornado
Lightning
Heavy Rainfall
Cloud Burst

67. Cumulus Stage Mature Stage
Dissipating Stage Cb Cloud

68. Present Doppler Weather Radar Network of IMD
S.
No
Station
Type of
DWR
Manufacturer
1.11 Chennai S-Band Gematronik (Germany)
2 Kolkata S-Band Gematronik (Germany)
3 Shriharikota S-Band Bharat Electronics Limited
4 Machilipatnam S-Band Gematronik (Germany)
5Vishakhapatnam S-Band Gematronik (Germany)
6 Delhi S-Band Metstar (Beijing)
7 Hyderabad S-Band Metstar (Beijing)
8 Nagpur S-Band Metstar (Beijing)
9 Agartala S-Band Metstar (Beijing)
10 Patna S-Band Metstar (Beijing)
11 Lucknow
S-Band
Metstar (Beijing)
12 Patiala S-Band Metstar (Beijing)
13 Mohanbari
S-Band
Metstar (Beijing)
14 Bhopal
S-Band
Metstar (Beijing)
15 Karaikal
S-Band
Metstar (Beijing)

69. Present Doppler Weather Radar Network of IMD
S.
No
Station Type of DWR Manufacturer
16. Goa S-Band Metstar(Beijing)
17. Paradip S-Band Metstar (Beijing)
18. Srinagar X-Band Toshiba (Japan)
19.Delhi (h.Q.) C-Band Polarimetric Vaisala (Finland)
20. Jaipur C-Band Polarimetric Vaisala (Finland)
21. Mumbai S-Band Bharat Electronics Limited
22. Bhuj S-Band do
23.Gopalpur S- Band do
24. Kochi S- Band do
25.Cherrapunji
S Band
do
26.Thiruanantpuram
C Band
do
27.Shriharikota
S Band
do

70. Present Doppler Weather Radar Network of IMD
S.S
No
Station Type of DWR Manufacturer
16.
Mukteshwar(UK) X-Band AMPL(India)
17.
Mussourie(UK) X-Band AMPL(India)
18.
Kufri(HP) X-Band AMPL(India)
19.
Lansdowne(UK) X-Band AMPL(India)
20.
Delhi X-Band AMPL(India)
21.
Jammu(J&K) X-Band AMPL(India)
22.
Leh X-Band AMPL(India)
23.
Banihal(J&K) X-Band AMPL(India)
24.
Dalhousie(HP) X-Band AMPL(India)
25.
Gangtok (Sikkim) X-Band AMPL(India)
26.
27.
1.1.

72. Standard Meteorological Products
Plan Position Indicator (PPI)(Z,V,W)
Range Height Indicator (RHI) (Z,V,W)
Max - Maximum display (MAX) (Z,V,W)
Constant Altitude PPI (CAPPI) (Z,V,W)
Pseudo CAPPI (PCAPPI) (Z,V,W)
Vertical Cut (VCUT) (Z,V,W)
Echo Top (ETOP) (Z)
Echo Base (EBAS) (Z)

73. Extended Meteorological Products
Volume Velocity Processing 2 (VVP2)
Uniform Wind Technique (UWT)
Vertical Integrated Liquid (VIL)
Combined Moment (CMM)
Spectrum at Maximum Velocity (SMV)
Storm Relative Velocity (SRV)
Severe weather Analysis Display (SWAD)

74. Wind Shear Detection Products
Radial Shear (RDS)
Azimuth Shear (AZS)
Elevation Shear (ELS)
Radial Azimuthal Shear (RAS)
Radial Elevation Shear (RES)
3D Shear (3DS)
Horizontal Shear (HZS)
Vertical Shear (VCS)

75. Warning and Forecasting Products
Hail Warning (HW)
Severe Weather Warning (SWW)
Storm Tracking (TRK)
Rain Tracking
Aviation Products
Layer Turbulence

76. Hydrological Products
Surface Rainfall Intensity (SRI)
Precipitation Accumulation (PAC)
Long Term Accumulation (LPAC)
Surface Hourly Rainfall (SHR)
River Sub-Catchment Accumulation (RSA)
Rainfall Intensity Histogram (RIM)
Point Rainfall Total (PRT)

77. Phenomena Detection and warning Products:-
a)Hail Detection (HHW)
b)Gust Detection (GUST)
c)Tornado Vortex Detection (TVS)
d)Cloud Motion Vector (CMV)
e) Meso Cyclone System Detection (MCS)

78. DESCRIPTION OF THE
DWR PRODUCTS
AND
THEIR ANALYSIS

79. Plan Position Indicator ( Z)
This product is obtained at a certain
elevation by azimuth scanning of the
antenna for 500 km range and shows all
echoes received in the radar range.
The intensity of the echoes is expressed in
dBz scale.
The product is useful in weather
surveillance of all kinds of severe weather
activities.

80. Plan Position Indicator ( Z) (Contd)
Depending upon the range of the target and
the angle of elevation the height of the echo is
estimated.
The nearby echoes correspond to lower heights
where as the farther echoes correspond to
higher altitude depending upon the range and
angle of elevation.
 The height of the radar beam increases with
the range due to curvature of the earth.

82. Maximum Reflectivity
(Max_Z)

83. (1) A top view as the highest measured values in Z-direction. This image shows the highest
measured value for each vertical column, seen from the top of the Cartesian volume.
(2) N-S view of highest measured values in Y-direction. This image is appended above top
view and show highest measured value for each horizontal line scan from north to south.
(3)E-W view of the highest measured values in X-direction. This image is appended to the right
of the top view and shows the highest measured value for each horizontal line scan from east
to west.
Max – Maximum Display

84. TOP VIEW
N-S VIEW
E-W VIEW

86. Constant Altitude PPI (Reflectivity)

This product displays echoes at user
defined altitude (above mean sea level).
The range of this product extends up to
500 km and height varies from 1 km to 18
km.
However, no data places are left blank in
the image as shown in figure on next
slide.

87. Constant Altitude PPI (Reflectivity)

89. Pseudo CAPPI (Reflectivity)Pseudo CAPPI (Reflectivity)
This product is similar to CAPPI except that " no data" areas of
the standard CAPPI close to the radar site and at large
ranges are filled with data of the corresponding elevation.
At short ranges the data are taken from the highest
elevation until this beam crosses the defined height and for
large ranges, where the lowest beam is higher than the
defined height, the data accumulations follow the lowest
beam.

91. •The VCUT displays a vertical cut through a
polar volume raw data set.
•The position of the vertical plane is defined
by two points A & B which can be located at
arbitrary positions.
•The displays shows height over distance with
point A at 0 Km. The main advantage of
VCUT from RHI, is that the positions of A
and B can be defined interactively in the
display manager
VCUT(Reflectivity)

95. The display shows the upper most height
where the measured value is within a user
defined range. This product is useful in
understanding the locations of the cloud tops
at various heights. The colour scale on the
right side of the picture shows the upper most
height of the echoes lying in the range of
reflectivity defined by the user.
Echo Top (Reflectivity)

97. Echo Base (Reflectivity)
The display shows the lower most height
where the measured value is within a user
defined range. This product is useful in
understanding the locations of the cloud
base at various heights. The colour scale
on the right side of the picture shows the
lower most height of the echoes lying in
the range of reflectivity defined by the
user.

99. It is an image of the rainfall intensity in a user selectable surface layer. It is calculated
based on Marshall-Palmer equation Z=AR
b
were R is the rainfall intensity and A and b
are constant. The value of A & b varies from season to season and place to place.
SRI – Surface Rainfall Intensity

101. Volume Velocity
Processing_2
• This product provides the vertical profile of
the horizontal winds over an area of radius 40
km from the DWR.
• VVP_2 provides a very good estimate of the
winds in the surrounding areas.

103. Assignments
How dBZ is expressed in the form of Z?
dBZ= 10 Log
10 (Z/ mm
6
/ m
3
)
What is ZR Relation? What is the utility of this equation?
Z = AR
b
. To convert Z in to R (Rainfall rate)
What are the values of A and b in the Marshal-Palmer Equation?
A=200 b=1.6
Are A and b constants for every place? Justify your answer.
No, A and b vary from place to place, Season to season and
from one type of rainfall to another.

104. What Max_Z image shows for a cloud? Explain the colour
table given in the image.
Shows the Horizontal Extent of the cloud, Vertical Extent
(Height of the cloud, Z value expressed in dBZ, Type of the
cloud, Cumulus, Cb, Line Squall etc.) Colour table shows
Radar Reflectivity according to the colour representation
of the cloud. Blue- Less Z and less rainfall, Red – More Z
indicates more rainfall.