Development of Spaceborne Dualfrequency Precipitation Radar and Its Role for the Global Precipitatio

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Development of Spaceborne Dual-frequency
Precipitation Radar and Its Role for the Global
Precipitation Measurement
Shinsuke Satoh (1), Riko Oki (1), Nobuhiro
Takahashi (2), and Toshio Iguchi (2) (1)
National Space Development Agency of Japan
(NASDA) (2) Communications Research Laboratory
(CRL), Japan 11 April 2003 in Nice, France
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The Concept of Global Precipitation Measurement
(GPM)

• Core Satellite
• Dual-frequency Precipitation Radar (DPR)
• Microwave Radiometer
• High-sensitivity precipitation measurement
• Calibration for constellation radiometers

• Constellation Satellites
• Microwave Radio-meters installed on each
  countrys satellite
• Frequent precipitation measurement

Expected Partners NASA, NOAA (US),
ESA (EU), NASDA, China, Korea, others
NASDA (Japan) DRP, H-IIA Launcher NASA
(US) Spacecraft, MWR
3-hourly global rainfall map
Blue Inclination 65º (GPM core) Green
Inclination 35º (TRMM)
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Concept of precipitation measurement
Flight direction
Dual-frequency precipitation radar (DPR) consists
of Ku-band (14GHz) radar (PR-U) and Ka-band
(35GHz) radar (PR-A)
GMI
DPR
Range resolution 250m
PR-U (13.6 GHz) swath width245 km
Microwave radiometer swath width 800km
PR-A (35.5 GHz) swath width100 km
5km
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Design of the GPM Core Satellite and the DPR
Ant cant angle (0 to 4 deg)
S/C nadir
PR-U
Harness connectors
Wave-guide connectors
PR-A
Wave-guide connectors
(by NASA/GSFC)
PR-A Additional radiation panel (?)
Basic design of the PR-U and PR-A is the almost
same as TRMM PR.
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Concept of the DPR antenna scan
PR-A 100 km (20 beams)
PR-U 245 km (49 beams)
In the interlacing scan area ( ), the PR-A can
measure snow and light rain in a high-sensitivity
mode with a double pulse width.
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Precipitation measurement with DPR
Detectable range of PR-A (35 GHz) ( cannot
measure heavy rainfall )
Matched beam of PR-A and PR-U
Detectable range of PR-U (14 GHz) ( cannot
measure light rain or snowfall)
Height
Sensitive observation by the PR-A
ICE
SNOW
Discrimination of snow and rain using
differential attenuation
Snowfall measurement in the frigid zones
MELTING LAYAR
PR-U
PR-A
RAIN
Accurate rainfall estimation using differential
attenuation (DSD parameter estimation)
Accurate rainfall measurement in the tropics and
the temperate zones
Radar reflectivity
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Dynamic Database provided by DPR for MWR
precipitation estimate algorithms
Another role of DPR is to provide Dynamic global
Database (every one day or a few days) for MWR
algorithms. The precipitation parameters vary in
seasons, times, and areas.

• Database of precipitation parameter
• DSD parameter (D0)
• Melting level (0?C height)
• Rainfall type (conv, strat, shallow,..)
• Rainfall uniformity information
• Storm height and mean profile

Rain-bands in a Typhoon
Snow clouds in the winter monsoon
MWR algorithms
More accurate precipitation estimated by MWRs on
the GPM constellation satellites
Stationary front and cloud clusters
Tropical cloud clusters
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DPR Specifications (Tentative)
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Variable PRF (VPRF) Technique
The observation range of spaceborne radar is only
20 km, while the distance between satellite and
the surface is 392 440 km. For that reason, the
receiving range window is located on after n-th
transmitting pulse. The Pulse Repetition
Frequency (PRF) of the DPR make vary to increase
the sampling number.
1/PRF
Distance between S/C and the surface target
Examples of VPRF
The distance is changed by Antenna scan angle (?9
km)
Proper PRF (?250 Hz) is determined on board
Satellite altitude (407 km?15 km) is measured by
GPS data
1/PRF
Distance between S/C and a surface target
Mode-1 245 km scan, Mode-2 100 km scan
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Current status of DPR development
The main aim is to develop light weight
components (wave-guide antenna, T/R module)
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DPR Development Schedule
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Summary

• The Dual-frequency Precipitation Radar (DPR)
  installed on the GPM core satellite, is currently
  being developed by NASDA and CRL.
• 2. The DPR will provide accurate estimates of
  rain rate,and light rain and snow data by
  high-sensitivity measurement.
• 3. The DPR will provide the dynamic global
  database of precipitation parameters (DSD,
  melting level, rain type, storm height, and so
  on) for the improvement of MWRs precipitation
  estimate algorithms.

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Backup Slides
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Beam Matching
Both radar should have the same foot print
location (requires good alignment and
synchronization)

• How well should the two beams match?
• - Answer depends on non-uniformity of rain
• Matched Beam requirement on the IFOV 0.1 ? 0.2
  km
• - Pointing allocation in S/C lt 0.1 deg (? 0.7 km)

Four kinds of mismatch - Dimensions and shape -
Cross-track direction - Along-track direction -
Scan direction
Concept for realizing matched beam. -
Cross-track direction adjust the beam direction
changing phase shifter control. - Along-track
direction set delay for one radar system.
Post-launch checkout. - Active radar calibrator
(ARC) experiment from ground to know the
alignment offset.
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Requirements for the Cant angle

• The cant angle range will be 0 to 4 degrees (4
  degrees in TRMM/PR case)
• It depends on an examination of surface clutter
  reduction

or
The radar beam direction is tilted to about 4
degrees off-nadir into the slot antenna direction
in order to improve the VSWR.
Beam direction ( S/C nadir) ltTRMM/PR casegt
Beam direction (? S/C nadir) ?slight conical scan
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Beam direction for the surface clutter reduction
In case of the beam tilted about 4 degrees from
the S/C nadir, the surface clutter may be reduced.
X
2 dimensional antenna pattern
Nadir direction from S/C
Main beam
Y
Main beam Strong sidelobe (gt -30 dB) Weak
sidelobe (-30 to -40 dB)
Amount of scattering from a surface ring may
contaminate the rain echoes detected by the main
beam.
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Improvement in the Accuracy of Rain Observation
by TRMM
(TMI PR)
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Observation by Constellation Satellites with
Microwave Radiometer
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Observation area with MWRs in 3 hours (1, 2, 4
and 8 satellites from top to bottom)
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Coverages by TRMM PR and GPM DPR in a day
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8
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International Satellite Constellation
G
TRMM PR,TMI
GPM core DPR,GMI
P
8
NPOESS-1,2,3 CMIS
7
Megha-Tropique
6
M
Number of Satellites
5
4
3
AMSR Follow-on
2
DMSP SSM/I
DMSP SSMIS
NPOESS CMIS
1
90
98
14
12
10
02
96
00
88
92
94
04
06
08
16
18
Year
Obs. Interval (Hour)
16
11
7
5
4
3
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Scientific and Social Significance of GPM

• Precision brought by DPR
• High sensitivity to detect light rain and snow
• Accurate estimation of rainfall rate
• Separation of snow from rain

• 3-hourly global rain map by GPM
• Climate change assessment
• Improvement in weather forecasts
• Flood forecasting (Flood Alert System)
• Water resource management
• Agricultural production forecasting

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Concept of GPM Data Network
GCOM-B1
GPM CORE
EGPM
Megha-Tripique
NPOESS
FY3
ARTEMIS
TDRS
DRTS
Users
NASA Ground Systems
NASDA Ground Systems
GPM Data Network (MWR L1 data)
ESA Ground Systems
French Ground Systems
Chinese Ground Systems
Indian Ground Systems
Users
Science Research
Weather
Disaster Monitoring
Education
Public Business
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Configuration of GPM Ground Systems
GPM sub satellites
GPM core satellite
DRTS(NASDA)
ARTEMIS(ESA)
TDRS
TDRS
NASDA GPM Ground Systems
Other Organizations
NASA
GPM L1 Network
GPM L1 Network
MWR Cal../ Processing
MWR Processing
GMI L1
L1 Products L2 Products L3 Products
L1 Products L2 Products L3 Products
GMI L2
MWR L1
GMI L2
DPR Processing
3hrs Rain Map Processing
MWR L1 Products
NASA PPS (Precipitation Processing System)
L1 Products L2 Products L3 Products
3H Rain Map Products
4DDA products
Operational Users
DPR L0
3H Rain Map
DPR/GMI Matching
3H Rain Map Products
JMA IFnet
DPR Processing
Data Archive
Science Users
DPR L2
SDPF
DPR L1,L2
TSDIS
Notes Red marked products show TBD.