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

Core Satellite• Dual-frequency Precipitation

Radar (DPR)• Microwave Radiometer

High-sensitivity precipitation measurementCalibration for constellation radiometers

Constellation Satellites

• Microwave Radio-meters installed on each country’s satelliteFrequent precipitation measurement

NASDA (Japan) : DRP, H-IIA Launcher

NASA (US) : 　Spacecraft, MWR

Expected Partners: NASA, NOAA (US), ESA (EU), NASDA, China, Korea, others

3-hourly global

rainfall map

The Concept of Global Precipitation Measurement (GPM)

2 satellites

8 satellites

Blue: Inclination ~65º (GPM core)Green: Inclination ~35º (TRMM)

Range resolution= 250m

PR-U (13.6 GHz) swath width=245 km

PR-A (35.5 GHz)swath width=100 km

DPR GMI

Microwave radiometer swath width =800km

Flight direction

5km

Dual-frequency precipitation radar (DPR) consists of Ku-band (14GHz) radar (PR-U) and Ka-band (35GHz) radar (PR-A)

Concept of precipitation measurement

Design of the GPM Core Satellite and the DPR

Harness connectors

PR-A

Wave-guide connectors

PR-A Additional radiation panel (?)

Ant cant angle (0 to +4 deg)

S/C nadir

PR-U

(by NASA/GSFC)

+x

PR-UPR-A

GMI

Basic design of the PR-U and PR-A is the almost same as TRMM PR.

Wave-guide connectors

Concept of the DPR antenna scanPR-U footprint : ∆z = 250 mPR-A footprint (Matched with PR-U) : ∆z = 250 mPR-A footprint (Interlaced) : ∆z = 500 m

PR-U: 245 km (49 beams)

PR-A: 100 km (20 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.

The synchronized matched beam ( ) is necessary for the dual-frequency algorithm.

Precipitation measurement with DPR

Hei

ght

Radar reflectivity

PR-APR-U

Discrimination of snow and rain using differential attenuation

Sensitive observation by the PR-A

Accurate rainfall estimation using differential attenuation(DSD parameter estimation)

Detectable range of PR-U (14 GHz)( cannot measure light rain or snowfall)

Detectable range of PR-A (35 GHz)( cannot measure heavy rainfall )Matched beam of

PR-A and PR-U

Snowfall measurement in the frigid zones

Accurate rainfall measurement in the tropics and the temperate zones

ICE

SNOW

RAIN

MELTING LAYAR

Dynamic Database provided by DPR for MWR precipitation estimate algorithmsAnother 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

More accurate precipitation estimated by MWRs on the GPM constellation satellites

MWR algorithms

Rain-bands in a Typhoon

Stationary front and cloud clusters

Snow clouds in the winter monsoon

Tropical cloud clusters

DPR Specifications (Tentative)

Active Phased Array 20

100km1.67/3.34 micro sec. (x2)

250 m/500m0.7 Deg.

5 kmVPRF (4500 Hz±250 Hz)

144W [current] 12dBZ (0.2 mm/hr) [target]

95 kbps290kg

306 W [max 331 W]1.3 ×1.0 ×0.7m

Active Phased Array 49

245 km1.67 micro sec. (x2)

250 m0.7 Deg.

5 kmVPRF (4000 Hz±250 Hz)

1000W17dBZ (0.4 mm/hr)

95 kbps370 kg

334 W [max 352 W]2.4×2.4×0.6 m

Antenna TypeBeam NumberSwath WidthPulse WidthRange ResolutionBeam WidthHorizontal ResolutionPRFPeak PowerSensitivityData RateWeightPower ConsumptionSize

35.5GHz radar (PR-A)13.6GHz radar (PR-U)Item

Variable PRF (VPRF) Technique

1 2 3 4 9 10 11

Transmit Receive

Pulse num

1/PRF

Distance between S/C and the surface target

The observation range of spaceborneradar 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-thtransmitting pulse. The Pulse Repetition Frequency (PRF) of the DPR make vary to increase the sampling number.

1.92.2

4.05.0

96 (n=11)112 (n=13)

2015

12

1.92.1

4.04.5

96 (n=11)104 (n=12)

2019

12

1.31.3

2.72.6

72 (n=8)72 (n=8)

2017

12

2020

H-obs(km)

60 (n=7)60 (n=7)

Sampling number(freq agility)

2.32.3

Center of PRF (Hz)

0.90.9

Gain(dB)

12

Mode

Examples of VPRF

1 2 3 4 9 10 11

Transmit Receive

Pulse num

1/PRF’

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

Distance between S/C and a surface target* Mode-1: 245 km scan, Mode-2: 100 km scan

Current status of DPR development

TRMM/PR type

TRMM/PR type

TRMM/PR type with GPS

T/R module(128 elements)

TRMM/PR type but lighter weight(128 elements)

Concept

Alignment between PR-U and PR-A

PR-A: radiation panel

- variable PRF - synchronized pulses- data compression

PR-U: MMIC (PHS, SW, MPA, LIM)PR-A: High power SSPA (35 GHz)

Half thick wave-guide slot antenna

Need to develop/study

Depending on the RF unit chip development and DPR operation mode.

Thermal design

Note

For better sensitivity and reduction of downlink data.Common components

Signal processing unit design

According to “matched beam”requirements.

Mechanical design

PR-U: BBM of T/R module (2003-04)PR-A: BBM of T/R module(2002-03 in CRL)

RF unit design

PR-U: completed (2000)PR-A: completed (in CRL)

Antenna design

# The main aim is to develop light weight components (wave-guide antenna, T/R module)

DPR Development Schedule

Summary1. 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 MWR’s precipitation estimate algorithms.

Backup Slides

Beam Matching

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 < 0.1 deg (∼ 0.7 km)

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

Four kinds of mismatch:- Dimensions and shape- Cross-track direction- Along-track direction- Scan directionConcept 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.

Requirements for the Cant angle

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)<TRMM/PR case>

• 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

Beam direction(≠ S/C nadir)→slight conical scan

or

Beam direction for the surface clutter reduction

Nadir direction from S/C

Main beam

Strong sidelobe (> -30 dB)

Weak sidelobe (-30 to -40 dB)

Main beam

Amount of scattering from a surface ring may contaminate the rain echoes detected by the main beam.

+X

+Y

2 dimensional antenna pattern

In case of the beam tilted about 4 degrees from the S/C nadir, the surface clutter may be reduced.

Improvement in the Accuracy of Rain Observation by TRMM

(TMI & PR)

Observation by Constellation Satellites with Microwave Radiometer

Observation area with MWRs in 3 hours(1, 2, 4 and 8 satellites from top to bottom)

Coverages byTRMM PR and

GPM DPR in a day

１

２

４

８

International Satellite Constellation

Ｇ

ＭＰ

8

7

6

5

4

3

2

1

90 98 1412100296 0088 92 94 04 06 08 16 18YearObs. Interval(Hour) ~16 ~11 ~7 ~5 ~4 ~3

DMSPSSM/I

DMSPSSMIS

NPOESSCMIS

TRMMPR,TMI

AQUAAMSR-E

ADEOS-IIAMSR AMSR Follow-on

GPM coreDPR,GMI

NPOESS-1,2,3CMIS

Num

ber o

f Sat

ellit

es

FY-3 (China)

Megha-Tropique

EGPS

NASA/Korea

Scientific and Social Significance of GPM

　

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

Precision brought by DPR– High sensitivity to detect light rain

and snow– Accurate estimation of rainfall rate– Separation of snow from rain

Concept of GPM Data Network

TDRS DRTS

GCOM-B1GPM COREEGPM Megha-Tripique NPOESS

ARTEMIS

FY3

GPM Data Network GPM Data Network (MWR L1 data)(MWR L1 data)

French Ground SystemsIndian Ground Systems Chinese Ground Systems

ESA Ground Systems

NASA Ground SystemsNASDA Ground Systems

Users

Users

Science & Research Weather Disaster Monitoring Education Public & Business

Users

Configuration of GPM Ground Systems

MWR ProcessingL1 ProductsL2 ProductsL3 Products

NASDA GPM Ground SystemsNASA

L2 Products

L1 Products

GMI Processing

DPR/GMIMatching

3H Rain Map　Products

3hrs Rain Map Processing

Other Organizations

DPR L0

DPR L2

DRTS(NASDA)

DPR L1,L2

GMI L1

GMI L2

MWR L1 Products

GPM core satellite

TDRS

GPM sub satellites

GPM L1Network

SDPF

TSDIS

DPR Processing

DPR Processing

L1 ProductsL2 ProductsL3 Products

Data Archive

L1 ProductsL2 ProductsL3 Products

MWR ProcessingL1 ProductsL2 ProductsL3 Products

GPM L1Network

ARTEMIS(ESA)

MWR L1 GMI L2

Notes: Red marked products show TBD.

TDRS

Science Users

Operational Users

3H Rain Map Products

4DDA products

MWR Cal../ Processing

NASA PPS(Precipitation

Processing System)

3H Rain Map

JMA

IFnet