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Toshio Iguchi National Institute of Information and Communications Technology iguchi@nict.go.jp iguchi@nict.go.jp Calibration of TRMM Precipitation Radar Achieving Satellite Instrument Calibration for Climate Change 16-18 May 2006 National Conference Center (NCC), Lansdowne, Virginia Slide 2 TRMMs Mission Objectives To advance the understanding of global circulation of energy and water from observation of tropical and subtropical rain Accurate measurement of tropical rain which affects the global climate monthly rain accumulation estimates in 5 deg by 5 deg boxes with less than 10% error (Sampling & Retrieval error) Estimation of vertical distribution of latent heat PR provides information on vertical rain profiles Slide 3 Orbit Altitude Inclination Circular Non-Sun Synchronous 350km (402.5km since Aug. 2001) (1.25km) 35 deg. Sensor Precipitation Radar (PR) TRMM Microwave Imager (TMI) Visible and Infrared Scanner (VIRS) Clouds and the Earths Radiation Energy System (CERES) Lightning (LIS) PR TMI VIRS LIS CERES High-gain antenna Solar paddle Observation of tropical rainfall (Driving engine of global atmosphere) US-Japan joint mission (Japan: PR, Launch, US: Bus, 4 sensors, operation) Launched in Nov., 1997. Still under operation First space-borne precipitation radar developed by CRL and NASDA Tropical Rainfall Measuring Mission: TRMM Slide 4 Concept of TRMM Rain Observation Flight Speed: 7.3 km/sec PR: Precipitation Radar TMI: TRMM Microwave Imager VIRS: Visible/IR Scanner Slide 5 Mission Requirements of TRMM PR Sensitivity < 0. mm/h Dynamic range > 70dB Horizontal resolution < km Range resolution < 250 Number of independent samples > 64 SD of fading noise 0.7 dB Swath width > 200km Observable range Surface to 15km Sensitivity < 0. mm/h Dynamic range > 70dB Horizontal resolution < km Range resolution < 250 Number of independent samples > 64 SD of fading noise 0.7 dB Swath width > 200km Observable range Surface to 15km Slide 6 Major Parameters of TRMM PR Radar typePulse radar Antenna type128-elem. WG slot array Beam scanningActive phased array Frequency13.796, 13.802 GHz PolarizationHorizontal TX/RX pulse width1.57 / 1.67 sec RX band width0.6 MHz Pulse rep. freq.2776 Hz Data rate93.5 kbps Mass460 kg Life time3 years TX peak power > 500 W (708 W) Antenna gain> 47.4 dB (47.5 dB) Beam width0.710.02 deg ( 0.71 deg) Min det. lv.< -110 dBm (-110.3 dBm) Min detectable RR< 0.7 mm/h (0.48 mm/h) Power cons.< 250 W (215 W) Radar typePulse radar Antenna type128-elem. WG slot array Beam scanningActive phased array Frequency13.796, 13.802 GHz PolarizationHorizontal TX/RX pulse width1.57 / 1.67 sec RX band width0.6 MHz Pulse rep. freq.2776 Hz Data rate93.5 kbps Mass460 kg Life time3 years TX peak power > 500 W (708 W) Antenna gain> 47.4 dB (47.5 dB) Beam width0.710.02 deg ( 0.71 deg) Min det. lv.< -110 dBm (-110.3 dBm) Min detectable RR< 0.7 mm/h (0.48 mm/h) Power cons.< 250 W (215 W) All numbers are designed values. The numbers in parentheses are the measured values with the PFM. Slide 7 Flow of Rain Profile Estimation Received Power (Pr) Conversion of Pr to Zm (Apparent measured radar reflectivity factor) using calibration factor of PR Pr Zm Assumptions: distribution of CLW as a function of R, distribution of WV, type of precipitating particles as a function of height, DSD model, homogeneity of rain distribution within an IFOV, vertical profile of rain in surface cluttered range, stable surface scattering cross sections Hardware Calibration Retrieval Algorithm Correction of attenuation due to CLW, WV, and O2 ZmZm' Correction of attenuation due to precipitating particles (rain att. correction assuming k-Ze relation (DSD)) Zm'Ze Conversion of Ze to R (rain rate) ZeR Slide 8 Z e : effective radar reflectivity factor, Z m : apparent measured radar reflectivity factor P r : received power --- internal & external cal. P t : TX power ------------ power monitor (and external cal.) G t0 : TX antenna gain --- (external cal.) G r0 : RX antenna gain --- (external cal.) t1, t2, r1, r2 : Tx and Rx antenna beam width (along and across track) --- (external cal.) r: range, : pulse width, c: speed of light, r : relative dielectric constant, n: refractive index : wavelength, k: specific attenuation Radar Equation where Slide 9 Hardware Calibration Calibrate the parameters in radar equation: Pt: Tx power of SSPA monitored Gt: Antenna gain for Tx, external cal. t: beam width, external cal Gr: Antenna gain for Rx, external cal. r: beam width, external cal Pr: Received power LNA cal, internal cal Overall calibration: external cal. Monitor the stability Temperatures at various places: Antenna panel, Panel, FCIF Power Supply Voltage SSPA Output Power System Noise Terminated Log-Amplifier Output Echoes from natural targets such as ocean surface Slide 10 TRMM PR Block Diagram (including redundancy units) SSPA:Solid State Power Amplifier LNA:Low Noise Amplifier PHS:Phase Shifter DIV/COMB:Divider/Combiner HYB:Hybrid TDA:Transmitter Drive Amplifier RDA:Receiver Drive Amplifier FCIF:Frequency Converter and IF SCDP:System Control Data Processor DIV/COMB HYB TDA RDA TDA BPFRDA FCIFSCDP FCIFSCDP BPF antenna SSPA LNA PHS antenna SSPA LNA PHS antenna SSPA LNA PHS 128 elements Slide 11 Housekeeping Records of TRMM PR(1/2) DIV/COMB RDA TDA FCIFSCDP antenna SSPA LNA PHS (1) Antenna Panel Temperature (2) Panel Temperature (3) FCIF Temperature Power Supply (4) Power Supply Voltage Slide 12 Housekeeping Records of TRMM PR(2/2) DIV/COMB RDA TDA FCIFSCDP antenna SSPA LNA PHS (5) SSPA Output Power Monitor at each Element (6) System Noise at each Angle Bin [ phase code at PHS is varied for all angle bins] (7) Terminated Log-Amplifier Output 128 elements Slide 13 Analysis Procedure of Housekeeping Records NameTypeUpdate time (1) Antenna Panel Temperature HK telemetry Realtime: 1 sec or 128 sec Playback: 10 sec (2) Panel Temperature (3) FCIF Temperature (4) Power Supply Voltage (5) SSPA Output Power Monitor Science telemetry 1 scan ( 0.6 sec) (6) System Noise (7) Terminated Log-Amplifier Output Housekeeping records of TRMM PR are included in two types of telemetry, HK telemetry and Science telemetry. Their update rate is frequent. In this analysis, some samples are collected approximately every 2 hours, and averaged in monthly. Four statistical values, average, standard deviation, minimum and maximum, are shown in the following plots. Table 1 Type and Update time of Housekeeping Records Slide 14 (1) Antenna Panel Temperature GSAGE/Sun Acquisition anomaly on 1999-003 Leonide Storm (mid-November) 350km altitude 400km altitude Slide 15 Summary of trends in housekeeping records Namestatus (1) Antenna Panel Temperature All PR temperatures have remained within limits, even during planned events like Deep Space Calibration and the Leonoid storm and anomalies like Low Power and Sun acquisition. (2) Panel Temperature (3) FCIF Temperature (4) Power Supply VoltagePower Supply Voltage have remained within limits. (5) SSPA Output Power Monitor All SSPAs work well, and their output powers are fairly stable except SSPA #011, #106. A steep change of SSPA #056 at Sep. 2000, a gradual decrease of SSPA #102 around May 2003 occurred, but now both SSPAs work stable. (6) System NoiseDigital Counts have remained within limits. (7) Terminated Log-Amplifier OutputDigital Counts have remained within limits. The effect of TRMMs altitude change, from 350 km to 400 km, does not appear in any housekeeping records variations. Slide 16 TRMM PR Internal Calibration DIV/COMB RDA TDA FCIFSCDP antenna SSPA LNA PHS Operation Analysis Mode measures the gain of each Rx channel by transmitting pulses with all 128 SSPA and receiving the echoes with only one LNA. Internal Calibration of FCIF & SCDP (with Transmit Power Off above Australia, every 3 days) Slide 17 Input-Output Characteristics of PR Receiver FCIF Unit RX input level (dBm) Output count value On-orbit measurement PFT results Linear fit of on-orbit data Slide 18 Transmit Antenna Aperture Power Distribution in Cross-track Direction Specification On-orbit measurement Note: SSPA power monitor telemetry is used. SSPA Number Transmit power (dBm) Slide 19 Receive Antenna Aperture Power Distribution in Cross-track Direction Note: Sea surface echo level with activating each LNA is used. Specification On-orbit measurement LNA Number Relative gain (dB) Slide 20 PR ARC Receiver PR ARC Transmitter PR ARC Delay Transponder (for PR TX)(for PR RX)(for TX/RX total) External Calibration with Active Radar Calibrator The ARC has tree functions : Radar transponder (Transponder mode) --- over all TX/RX system Radar receiver (RX mode) --- PR TX power, antenna pattern, PR TX antenna gain Beacon transmitter (TX mode) --- PR RX gain, antenna pattern Slide 21 (PR/TXARC/RX) 0.735 deg 28.2dB Tx Antenna pattern Slide 22 (PR/RXARC/TX) 0.717 deg Rx Antenna pattern Slide 23 Along-track PR Receive Antenna Pattern Angle (deg) Relative Gain (dB) After Launch Before Launch Slide 24 Trend of PR Receiver Performance 13 ARC PR 1997/12/15 2005/12/10 Trend of Rx power with ARC used as a transmitter orbit change Slide 25 Trend of PR Transmitter Performance 03/1004/0404/1005/0405/10 UT dB Ver. Ver. Ver. Ver. (measured value) - (calculated value) (dB) Measurement date (year/month) Trend of Tx power of PR with ARC used as a receiver 1.0 -2.0 0.0 2.0 orbit change f2 is used for comparison Slide 26 Trend of PR Overall Gain 05/0405/10 UT dB Ver. Ver. Ver. Ver. (measured value) - (calculated value) (dB) Measurement date (year/month) Trend of overall PR gain with ARC used as a transponder 1.0 -2.0 0.0 3.0 2.0 -3.0 orbit change f2 is used for comparison Slide 27 Incidence Angle Dependence of Ocean Sigma-0 Measured by TRMM PR 2/14 3/6 1998 18 ARMAR CAMPR No rain cases, 18 orbits in Feb 14 - Mar. 6, 1998 Incidence Angle (deg) Normd radar cross-section (dB) Slide 28 Monthly variations of sea surface echoes Variation of normalized sea surface radar cross section (no-rain cases) Slide 29 Variability of sea surface echoes Slide 30 July 1998 January 1999 Global Distribution of the Mean Storm Height Measured by the TRMM Precipitation Radar Slide 31 Tropical Rainfall Anomalies (TRMM Ocean Retrievals) V5 Slide 32 BB Height and Freezing Level Brightband Height Freezing Level (3A11) 10S-10N 30S-30N 20S-20N (170E-230E) Slide 33 Freezing Level and BB 10S-10N 30S-30N 20S-20N FL - BB BB FL (30S-0, 0-30N) (170E-230E) Slide 34 Comparison of rain estimates from different algorithms (PR and TMI) (Essentially the same as V6) Slide 35 TMI V6, PR V5(W. Berg, et al.) PR and TMI Regional Validation Slide 36 Summary TRMM PR uses three kinds of calibration methods. internal calibration external calibration with ARC calibration with natural targets PR's electric and electronic performance was measured in the initial check-up period just after launch. absolute calibration error < 1dB All calibration methods indicate an extremely stable performance of PR. HK data are all very stable overall long-term stability < 0.05dB The largest error in rain rate estimation probably comes from the retrieval algorithms and not from the radar calibration. Slide 37 Acknowledgments H. Hanado (JAXA) N. Takahashi (NICT) K. Okamoto (Osaka Prefecture University) JAXA/EORC and many other people who helped me. Slide 38 Backup slides Slide 39 External Calibration of DPR 0.1775 (=1.25km) ARC scan direction flight direction 0.2 Rx Improvement of angular resolution. Multiple receivers (or ARCs) will improve the along track resolution. PR and DPR calibration scan strategy Observed & retrieved 2D patterns by ARC Slide 40 Variations in System Noise (TRMM PR) by Takahashi and Iguchi:IGARSS-2004 The system noise level is determined by the thermal noise and the background noise from the radiation of the earth surface, precipitation, etc. The variation of the thermal noise is less than 0.15 dB, and is stable for a long period (Left Figure). The variation of the background noise is also small (< 0.1 dB over ocean, < 0.5 dB over land) The fading variation of the system noise is about 1 dB (Right Figure). Long-term change of the system noise and the solar beta angle (top), and the FCIF temperature (bottom) frequency An example of the system noise distribution (no-rain, over ocean, 100 orbits data) Slide 41 TRMM implemented 180 deg. yaw manuevour when the solar beta angle reaches to zero. Long term trend of (sampled) system noise Good agreement with the FCIF temperature change The temperature change is relating to the solar beta angle The fluctuation of the system noise is about 0.15 dB The system noise shifts by about 0.05 dB after the PR power off event Sun acquisition mode average for one orbit to remove the fading effect Slide 42 Changes in one orbit Changes in the system noise when the satellite moves from the sunny side to shadow side. The changes in system noise delays about 4 hours in local time (about 20 minutes in actual time) No clear dependency can be seen for low solar beta angles. Slide 43 Differences in Rain Estimates 10S-10N 30S-30N 20S-20N 1998199920002001 2002 2A25 2A12 ERA-40 3B42 170E-230E Slide 44 Climate Variability Models vs. Observations Slide 45 Tropical Mean Rainfall Variability Slide 46 Bias Adjusted Mean DJF Rainfall (TRMM Retrievals) Slide 47 Tropical Rainfall Anomalies (Passive Microwave Algorithms) Slide 48 Tropical Rainfall Anomalies (TRMM Land Retrievals) Slide 49 (Higashiuwatoko) Slide 50 J. Kwiatkowski Slide 51 Slide 52 Diurnal Variation of Rain from PR Afternoon rain (local time: 12-18 h) Morning rain (local time: 6-12 h) Morning rain dominantAfternoon rain dominant (March 1998 - February 1999) 10 -10