Toshio Iguchi National Institute of Information and Communications Technology [e-mail]

1
Calibration of TRMM Precipitation Radar

• Toshio IguchiNational Institute of Information
  and Communications Technologyiguchi_at_nict.go.jp

Achieving Satellite Instrument Calibration for
Climate Change
16-18 May 2006 National Conference Center
(NCC), Lansdowne, Virginia
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

3
Tropical Rainfall Measuring Mission TRMM
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
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)
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Concept of TRMM Rain Observation
Flight Speed 7.3 km/sec
PR Precipitation Radar TMI TRMM Microwave
Imager VIRS Visible/IR Scanner
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Mission Requirements of TRMM PR
Sensitivitylt 0.7mm/h Dynamic rangegt
70dB Horizontal resolutionlt 5km Range
resolutionlt 250m Number of independent
samplesgt 64 (SD of fading noise lt 0.7 dB) Swath
widthgt 200km Observable rangeSurface to 15km
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Major Parameters of TRMM PR
Radar type Pulse radar Antenna type 128-elem. WG
slot array Beam scanning Active phased
array Frequency 13.796, 13.802 GHz Polarization Ho
rizontal TX/RX pulse width 1.57 / 1.67 msec RX
band width 0.6 MHz Pulse rep. freq. 2776 Hz Data
rate 93.5 kbps Mass 460 kg Life time 3 years TX
peak power gt 500 W (708 W) Antenna gain gt 47.4
dB (47.5 dB) Beam width 0.710.02 deg ( 0.71
deg) Min det. lv. lt -110 dBm (-110.3 dBm) Min
detectable RR lt 0.7 mm/h (0.48 mm/h) Power
cons. lt 250 W (215 W)
All numbers are designed values. The numbers in
parentheses are the measured values with the PFM.
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Flow of Rain Profile Estimation
Hardware Calibration

• Received Power (Pr)
• Conversion of Pr to Zm (Apparent measured radar
  reflectivity factor) using calibration factor of
  PR
• Pr ?Zm

Retrieval Algorithm

• Correction of attenuation due to CLW, WV, and O2
• Zm?Zm'
• Correction of attenuation due to precipitating
  particles (rain att. correction assuming k-Ze
  relation (DSD))
• Zm'?Ze
• Conversion of Ze to R (rain rate)
• Ze?R

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
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Radar Equation
where
Ze effective radar reflectivity factor, Zm
apparent measured radar reflectivity factor Pr
received power --- internal external cal. Pt
TX power ------------ power monitor (and external
cal.) Gt0 TX antenna gain --- (external
cal.) Gr0 RX antenna gain --- (external
cal.) qt1, qt2, qr1, qr2 Tx and Rx antenna beam
width (along and across track) --- (external
cal.) r range, t pulse width, c speed of
light, er relative dielectric constant, n
refractive index l wavelength, k specific
attenuation
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Hardware Calibration

• Calibrate the parameters in radar equation
• Pt Tx power of SSPA monitored
• Gt Antenna gain for Tx, external cal.
• qt beam width, external cal
• Gr Antenna gain for Rx, external cal.
• qr 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

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TRMM PR Block Diagram (including redundancy units)
SSPA Solid State Power AmplifierLNA Low
Noise AmplifierPHS Phase ShifterDIV/COMB Divi
der/CombinerHYB HybridTDA Transmitter Drive
Amplifier RDA Receiver Drive
Amplifier FCIF Frequency Converter and
IFSCDP System Control Data Processor
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Housekeeping Records of TRMM PR(1/2)
(3) FCIF Temperature
DIV/COMB
RDA
(4) Power Supply Voltage
Power Supply
(1) Antenna PanelTemperature
(2) Panel Temperature
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Housekeeping Records of TRMM PR(2/2)
(5) SSPA Output Power Monitor at each Element
(7) Terminated Log-Amplifier Output
128 elements
(6) System Noise at each Angle Binphase code at
PHS is varied for all angle bins
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Analysis Procedure of Housekeeping Records
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
Name Type Update time
(1) Antenna Panel Temperature HK telemetry Realtime 1 sec or 128 sec Playback 10 sec
(2) Panel Temperature HK telemetry Realtime 1 sec or 128 sec Playback 10 sec
(3) FCIF Temperature HK telemetry Realtime 1 sec or 128 sec Playback 10 sec
(4) Power Supply Voltage HK telemetry Realtime 1 sec or 128 sec Playback 10 sec
(5) SSPA Output Power Monitor Science telemetry 1 scan ( 0.6 sec)
(6) System Noise Science telemetry 1 scan ( 0.6 sec)
(7) Terminated Log-Amplifier Output Science telemetry 1 scan ( 0.6 sec)
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(1) Antenna Panel Temperature
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Summary of trends in housekeeping records
Name status
(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 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.
(3) FCIF 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.
(4) Power Supply Voltage Power 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 Noise Digital Counts have remained within limits.
(7) Terminated Log-Amplifier Output Digital 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.
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TRMM PR Internal Calibration
Internal Calibration of FCIF SCDP(with
Transmit Power Off above Australia, every 3 days)
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.
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Input-Output Characteristics of PR Receiver FCIF
Unit
Output count value
? On-orbit measurement PFT results Linear
fit of on-orbit data
RX input level (dBm)
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Transmit Antenna Aperture Power Distribution in
Cross-track Direction
On-orbit measurement
Transmit power (dBm)
Specification
Note SSPA power monitor telemetry is used.
SSPA Number
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Receive Antenna Aperture Power Distribution in
Cross-track Direction
On-orbit measurement
Relative gain (dB)
Specification
Note Sea surface echo level with activating each
LNA is used.
LNA Number
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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
PR
PR
PR
ARC Receiver
ARC Transmitter
ARC Delay Transponder
(for PR TX)
(for PR RX)
(for TX/RX total)
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Tx Antenna pattern
(PR/TX?ARC/RX)
0.735 deg
28.2dB
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Rx Antenna pattern
(PR/RX?ARC/TX)
0.717 deg
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Along-track PR Receive Antenna Pattern
Relative Gain (dB)
Angle (deg)
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Trend of PR Receiver Performance
Trend of Rx power with ARC used as a transmitter
??-13 ARC?????/PR???????????(1997/12/152005/12/10
)
orbit change
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Trend of PR Transmitter Performance
Trend of Tx power of PR with ARC used as a
receiver
2.0
Ver.3
Ver.4
Ver.5
Ver.6
1.0
(measured value) - (calculated value) (dB)
0.0
(???)-(???)(dB)
-1.0
orbit change
-2.0
03/10
04/04
04/10
05/04
05/10
???(UT)
Measurement date (year/month)
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Trend of PR Overall Gain
Trend of overall PR gain with ARC used as a
transponder
3.0
Ver.3
Ver.4
Ver.5
Ver.6
2.0
1.0
0.0
(measured value) - (calculated value) (dB)
(???)-(???)(dB)
-1.0
-2.0
orbit change
-3.0
05/04
05/10
Measurement date (year/month)
???(UT)
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Incidence Angle Dependence of OceanSigma-0
Measured by TRMM PR
No rain cases, 18 orbits in Feb 14 - Mar. 6, 1998
??????? 2/143/6 1998?18??
ARMAR
Normd radar cross-section (dB)
CAMPR
Incidence Angle (deg)
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Monthly variations of sea surface echoes
Variation of normalized sea surface radar cross
section
(no-rain cases)
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Variability of sea surface echoes
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Global Distribution of the Mean Storm Height
Measured by the TRMM Precipitation Radar
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Tropical Rainfall Anomalies(TRMM Ocean
Retrievals)
V5
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BB Height and Freezing Level
(170E-230E)
Freezing Level (3A11)
Brightband Height
10S-10N
20S-20N
30S-30N
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Freezing Level and BB
(170E-230E)
FL - BB
FL (30S-0, 0-30N)
10S-10N
BB
20S-20N
FL-BB
30S-30N
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Comparison of rain estimates from different
algorithms (PR and TMI)
(Essentially the same as V6)
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PR and TMI Regional Validation
TMI V6, PR V5
(W. Berg, et al.)
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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 lt 1dB
• All calibration methods indicate an extremely
  stable performance of PR.
• HK data are all very stable
• overall long-term stability lt 0.05dB
• The largest error in rain rate estimation
  probably comes from the retrieval algorithms and
  not from the radar calibration.

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Acknowledgments

• H. Hanado (JAXA)
• N. Takahashi (NICT)
• K. Okamoto (Osaka Prefecture University)
• JAXA/EORC
• and many other people who helped me.

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Backup slides
39
External Calibration of DPR
PR and DPR calibration scan strategy
Observed retrieved 2D patterns by ARC
Improvement of angular resolution. Multiple
receivers (or ARCs) will improve the along track
resolution.
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Variations in System Noise (TRMM PR)

• 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 (lt 0.1 dB over ocean, lt 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)
An example of the system noise distribution
(no-rain, over ocean, 100 orbits data)
by Takahashi and IguchiIGARSS-2004
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Long term trend of (sampled) system noise
average for one orbit to remove the fading effect
TRMM implemented 180 deg. yaw manuevour when the
solar beta angle reaches to zero.
Sun acquisition mode

• 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

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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.

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Differences in Rain Estimates
170E-230E
2A25 2A12 ERA-40 3B42
10S-10N
20S-20N
30S-30N
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Climate Variability Models vs. Observations
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Tropical Mean Rainfall Variability
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Bias Adjusted Mean DJF Rainfall (TRMM Retrievals)
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Tropical Rainfall Anomalies(Passive Microwave
Algorithms)
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Tropical Rainfall Anomalies(TRMM Land Retrievals)
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(Higashiuwatoko)
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J. Kwiatkowski
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J. Kwiatkowski
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Diurnal Variation of Rain from PR
Morning rain dominant
Afternoon rain dominant
(March 1998 - February 1999)