Spaceborne Dualfrequency Precipitation Radar for Global Precipitation Measurement

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Spaceborne Dual-frequency Precipitation Radar for
Global Precipitation Measurement
Shinsuke Satoh (1), Riko Oki (1), Toshio Iguchi
(2), and Kenji Nakamura (3) (1) National Space
Development Agency of Japan (NASDA) (2)
Communications Research Laboratory (CRL) (3)
Hydrospheric Atmospheric Research Center (HyARC),
Nagoya University 30 June 2003 IUGG,
JSM18_at_Sapporo
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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 by the GPM
core satellite
Dual-frequency precipitation radar (DPR) consists
of Ku-band (14GHz) radar KuPR and Ka-band
(35GHz) radar KaPR
Flight direction
GMI
DPR
Range resolution 250m
KuPR (13.6 GHz) swath width245 km
Microwave radiometer swath width 800km
KaPR (35.5 GHz) swath width100 km
5km
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DPR Specifications (Requirements)

• Sensitivity is calculated by equiv-SNR at the
  top of precipitation (SNR1 in 1-pulse). Noise
  sampling
• number is 4-times as much as the averaging
  sampling number. Rain rate is defined by
  Z200R1.6

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Concept of the DPR antenna scan
49
37
49
38
13
12
1
1
KaPR 120 km (24 beams)
KuPR 245 km (49 beams)
In the interlacing scan area ( ), the KaPR 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 KaPR (35 GHz) ( cannot
measure heavy rainfall )
Matched beam of KuPR and KaPR
Detectable range of KuPR (14 GHz) ( cannot
measure light rain or snowfall)
Height
Sensitive observation by the KaPR
ICE
SNOW
Discrimination of snow and rain using
differential attenuation
Snowfall measurement in the frigid zones
MELTING LAYAR
KuPR
KaPR
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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DPR Dynamic Database for MWR precipitation
retrieval algorithms
Another role of DPR is to calibrate MWR
precipitation estimates using Dynamic global
Database (renewal every 3-10 days). The
precipitation parameters vary in seasons, times,
and areas.

• Database of precipitation parameter
• DSD parameter (D0)
• Rain type (conv, strat, shallow,)
• Freezing level (0?C height)
• Storm height
• (Rainfall uniformity information)
• Mean precipitation 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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Concept of a DPR-calibrated MWR precipitation
algorithm
Global Precipitation Map
NASA, ESA, China, (Quasi-real-time data)
Cut-off time
MWR L1 data
Precipitation Retrieval
L2 (precip) data Composition
Pre-proc

• Quality check
• Rain/no-rain
• Conv/Strat percentage
• In-homogeneity

Unavailable data
DPR data proc system (NASDA)
DPR dynamic Database
Look-up Tables for each MWR (TBs vs Precip)
RTM Calc.
Antenna Convolution

• DSD, Precip-class
• Storm height
• Freezing level
• Mean Precip profile
• (Ocean/Land/Conv/Strat)

• Surface temp
• Humidity

GANAL

• Surface condition (emissivity)

Surface DB
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Time and space Interval of the DPR database
1-day orbit
3-days orbit
Color IFOV pixel num
Color orbit num
0.5?0.5deg
?100 pixels
One-day orbit observations of DPR (upper) and GMI
(lower)
?100 pixels
DPR dynamic database will be renewed in 15 deg ?
5 deg grids every 3-10 days
The orbit data was calculated by Y.Iida (Osaka
Prefecture Univ)
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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, Storm
  height, Freezing level, Rain type, and so on) for
  accurate MWR precipitation retrieval algorithms.

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Backup Slides
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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-1 250 m reso, Mode-2 500 m reso
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Detectability

• Definition of minimum detectable signal?
• Effective S/N Ye
• Y true S/N (S/N for one pulse)
• N of signal samples (N64)
• M of noise samples (M4N256)
• cT correction term for log-detection (1.283)

If Y1 and N64, then Ye3.02 (4.81 dB) If Y1
and N96, then Ye3.70 (5.69 dB) If Y1 and
N104, then Ye3.86 (5.86 dB)
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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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Observation by Constellation Satellites with
Microwave Radiometer
1
Observation area with MWRs in 3 hours (1, 2, 4
and 8 satellites from top to bottom)
2
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
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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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Design of the GPM Core Satellite and the DPR
GMI
x
Flight Direction
KaPR
KuPR
KaPR Additional radiation panel
KuPR
Wave-guide connectors
KaPR
Basic design of KuPR and KaPR is the almost same
as TRMM PR.
(Spacecraft design by NASA/GSFC)
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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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DPR Products (draft)
It is possible to process the level-2 and 3
data in the scene unit of 1/2 or 1/3 orbit
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DPR/MWR Combined Products (Global Precipitation
Map)
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Improvement in the Accuracy of Rain Observation
by TRMM
(TMI PR)
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DPR development schedule
Reviews in NASDA
DLR
PRR2
PRR1
CDR (KuPR)
CDR (KaPR)
PDR
Launch
PIDR
PQR/PSR
Init.C/O
Normal Operation
Preliminary Design
Critical Design
Conceptual Design
Sustaining Design
Investigation
S/C-system Support
TR-unit BBM (KuPR)
PFM (KuPR)
Component Experiment
DPR Integration
Launch Operation (NASA/JAXA)
EM (KaPR)
PFM (KaPR)
RF-unit EM (CRL)
Comp. Exp
BBM (CRL)
15 months
Integration MST
Normal Operation
Ground System Design Fabrication
OperTrain
Init Oper
Cal/Val
Investigation
Algorithm Examination
Improvement
Algorithm Development Test
Data Analysis and Research
RA
RI
Install Test
Critical Design
Preliminary Design
FM Fabrication Assembly
PQR/PSR
PRR Project Readiness Review, PIDR Preliminary
Interface Design Review, PDR Preliminary Design
Review, CDR Critical Design Review, MST
Mission Simulation Test, PQR Post
Qualification-test Review, PSR Pre-Shipment
Review, DLR Delivery Review, T/R-unit
Transmitter/Receiver unit, RF-unit
Radio-Frequency unit (including antenna and T/R
component)