Development of Spaceborne Dualfrequency. and Its Role for the Global Precipitation Measurement

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1 Development of Spaceborne Dualfrequency 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

2 The Concept of Global Precipitation Measurement (GPM) Core Satellite Dual-frequency Precipitation Radar (DPR) Microwave Radiometer High-sensitivity precipitation measurement Calibration for constellation radiometers NASDA (Japan) : DRP, H-IIA Launcher NASA (US) : Spacecraft, MWR Blue: Inclination ~65º (GPM core) Green: Inclination ~35º (TRMM) 3-hourly global rainfall map Constellation Satellites Microwave Radiometers installed on each country s satellite Frequent precipitation measurement Expected Partners: NASA, NOAA (US), ESA (EU), NASDA, China, Korea, others 2 satellites 8 satellites

3 Concept of precipitation measurement Dual-frequency precipitation radar (DPR) consists of Ku-band (14GHz) radar (PR-U) and Ka-band (35GHz) radar (PR-A) DPR Flight direction GMI Range resolution = 250m PR-U (13.6 GHz) swath width=245 km PR-A (35.5 GHz) swath width=100 km Microwave radiometer swath width =800km 5km

4 Design of the GPM Core Satellite and the DPR Ant cant angle (0 to +4 deg) S/C nadir GMI +x PR-U Harness connectors PR-A PR-U (by NASA/GSFC) Basic design of the PR-U and PR-A is the almost same as TRMM PR. PR-A PR-A Additional radiation panel (?) Wave-guide connectors Wave-guide connectors

5 Concept of the DPR antenna scan PR-U footprint : z = 250 m PR-A footprint (Matched with PR-U) : z = 250 m PR-A footprint (Interlaced) : z = 500 m 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 highsensitivity mode with a double pulse width. The synchronized matched beam ( ) is necessary for the dual-frequency algorithm.

6 Precipitation measurement with DPR Matched beam of PR-A and PR-U Detectable range of PR-A (35 GHz) ( cannot measure heavy rainfall ) Detectable range of PR-U (14 GHz) ( cannot measure light rain or snowfall) ICE Height Sensitive observation by the PR-A Snowfall measurement in the frigid zones SNOW MELTING LAYAR PR-A PR-U Discrimination of snow and rain using differential attenuation RAIN Accurate rainfall estimation using differential attenuation (DSD parameter estimation) Accurate rainfall measurement in the tropics and the temperate zones Radar reflectivity

7 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. Rain-bands in a Typhoon Stationary front and cloud clusters Database of precipitation parameter - DSD parameter (D 0 ) - Melting level (0 C height) - Rainfall type (conv, strat, shallow,..) - Rainfall uniformity information - Storm height and mean profile MWR algorithms More accurate precipitation estimated by MWRs on the GPM constellation satellites Snow clouds in the winter monsoon Tropical cloud clusters

8 DPR Specifications (Tentative) Item Antenna Type Beam Number Swath Width Pulse Width Range Resolution Beam Width Horizontal Resolution PRF Peak Power Sensitivity Data Rate Weight Power Consumption Size 13.6GHz radar (PR-U) Active Phased Array km 1.67 micro sec. (x2) 250 m 0.7 Deg. 5 km VPRF (4000 Hz±250 Hz) 1000W 17dBZ (0.4 mm/hr) 95 kbps 370 kg 334 W [max 352 W] m 35.5GHz radar (PR-A) Active Phased Array km 1.67/3.34 micro sec. (x2) 250 m/500m 0.7 Deg. 5 km VPRF (4500 Hz±250 Hz) 144W [current] 12dBZ (0.2 mm/hr) [target] 95 kbps 290kg 306 W [max 331 W] m

9 Variable PRF (VPRF) Technique Pulse num Transmit Receive /PRF Distance between S/C and the surface target 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. Satellite altitude (407 km±15 km) is measured by GPS data Proper PRF (±250 Hz) is determined on board The distance is changed by Antenna scan angle (±9 km) Mode 1 2 Examples of VPRF H-obs (km) Sampling number (freq agility) 60 (n=7) 60 (n=7) Center of PRF (Hz) Gain (db) Transmit Receive (n=8) 72 (n=8) Pulse num /PRF Distance between S/C and a surface target (n=11) 104 (n=12) 96 (n=11) 112 (n=13) * Mode-1: 245 km scan, Mode-2: 100 km scan

10 Current status of DPR development Concept Need to develop/study Note Antenna design TRMM/PR type but lighter weight (128 elements) Half thick wave-guide slot antenna PR-U: completed (2000) PR-A: completed (in CRL) RF unit design T/R module (128 elements) PR-U: MMIC (PHS, SW, MPA, LIM) PR-A: High power SSPA (35 GHz) PR-U: BBM of T/R module ( ) PR-A: BBM of T/R module ( in CRL) Signal processing unit design TRMM/PR type with GPS -variable PRF - synchronized pulses - data compression For better sensitivity and reduction of downlink data. Common components Thermal design TRMM/PR type PR-A: radiation panel Depending on the RF unit chip development and DPR operation mode. Mechanical design TRMM/PR type Alignment between PR-U and PR-A According to matched beam requirements. # The main aim is to develop light weight components (wave-guide antenna, T/R module)

11 DPR Development Schedule

12 Summary 1. 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.

13 Backup Slides

14 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: km - Pointing allocation in S/C < 0.1 deg ( 0.7 km) 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. Four kinds of mismatch: - Dimensions and shape - Cross-track direction - Along-track direction - Scan direction Post-launch checkout. - Active radar calibrator (ARC) experiment from ground to know the alignment offset.

15 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) <TRMM/PR case> Beam direction ( S/C nadir) slight conical scan

16 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 Amount of scattering from a surface ring may contaminate the rain echoes detected by the main beam. Main beam Strong sidelobe (> -30 db) Weak sidelobe (-30 to -40 db) +Y

17 Improvement in the Accuracy of Rain Observation by TRMM (TMI & PR)

18 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 by TRMM PR and GPM DPR in a day

19 International Satellite Constellation 8 TRMM PR,TMI GPM core DPR,GMI NPOESS-1,2,3 CMIS Number of Satellites AQUA AMSR-E ADEOS-II AMSR Megha-Tropique FY-3 (China) EGPS NASA/Korea AMSR Follow-on 2 1 DMSP SSM/I DMSP SSMIS NPOESS CMIS Year Obs. Interval (Hour) ~16 ~11 ~7 ~5 ~4 ~3

20 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

21 Concept of GPM Data Network EGPM Megha-Tripique GPM CORE NPOESS FY3 GCOM-B1 ARTEMIS TDRS DRTS Users ESA Ground Systems Users NASA Ground Systems GPM Data Network (MWR L1 data) NASDA Ground Systems French Ground Systems Indian Ground Systems Chinese Ground Systems Users Science & Research Weather Disaster Monitoring Education Public & Business

22 Configuration of GPM Ground Systems GPM core satellite GPM sub satellites DRTS(NASDA) ARTEMIS(ESA) TDRS NASA NASDA GPM Ground Systems TDRS Other Organizations GMI Processing L1 Products L2 Products NASA PPS (Precipitation Processing System) 3H Rain Map GPM L1 Network DPR L0 GMI L1 GMI L2 DPR Processing L1 Products L2 Products L3 Products MWR L1 MWR Cal../ Processing L1 Products L2 Products L3 Products 3hrs Rain Map Processing 3H Rain Map Products DPR/GMI Matching GMI L2 GPM L1 Network 4DDA products 3H Rain Map Products MWR Processing L1 MWR Products Processing L2 ProductsL1 Products L3 ProductsL2 Products L3 Products MWR L1 Products Operational Users JMA DPR Processing DPR L2 Data Archive Science Users IFnet SDPF DPR L1,L2 TSDIS Notes: Red marked products show TBD.