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WindSat:Passively MeasuringOcean Vector Winds
(and other things)
Ian S. AdamsMichael H. Bettenhausen
Peter W. GaiserLi Li
Remote Sensing Physics BranchNaval Research Laboratory
1
Mission Status
2
• Demonstrate passive wind vector measurements from space
• Risk reduction for NPOESS MIS
• 7 years of successful ops
• NRL Responsible for Science, Payload Development, Mission Management, Vehicle Integration, and Cal/Val
WindSat Band Descriptions
3
Freq.(GHz) Channels BW
(MHz)EIA
(deg)IFOV(km)
6.8 v/h 125 54.0 39 x 7110.7 v/h, +/– 45, lc/rc 300 50.3 25 x 3818.7 v/h, +/– 45, lc/rc 750 55.9 16 x 2723.8 v/h 500 53.5 20 x 3037.0 v/h, +/– 45, lc/rc 2000 53.5 8 x 13
990922_WS_CDR_AntSys.16
Feedhorn Location RequirementsFeedhorn Location Requirements
0,0
6.8GHz V/H
10.7GHz ±45 10.7GHz CP 10.7GHz V/H
18.7GHz V/H18.7GHz ±45 18.7GHz CP
23.8GHz V/H
37GHz V/H37GHz ±45
37GHz CP
+ XF
- YF
- XF
+ YF
Notes:
Feed Bench View From Main Reflector
Feed Bench Coordinate Origin At 37 GHzCP Horn Phase Center
Horns Sets Located on Four “GreatCircles” Resulting in Four Different EIA’s
Offset Horn Lateral Locations Not CriticalAs Long As They Remain on, or Can BeAdjusted to, Great Circles
Spin Axis
Feed Freq. (GHz) Polarization
X Location
Y Location
Z Location
6.8 V/H 0.206 9.963 0.261
10.7 ±45 3.137 4.492 -0.033
10.7 CP 2.995 0.000 0.182
10.7 V/H 3.137 -4.492 -0.033
18.7 ±45 -2.157 2.712 -0.013
18.7 CP -2.202 0.000 -0.216
18.7 V/H -2.157 -2.712 -0.013
23.8 V/H 0.448 -8.102 0.413
37.0 ±45 0.034 2.249 0.036
37.0 CP 0.000 0.000 0.000
37.0 V/H 0.034 -2.249 0.036
Warm Load Side
Cold Load Side
11 feed horns
22 measured antenna
temperatures
WindSat Data Usage
4
• Assimilation• NOGAPS
• NCEP
• UK Met Office
• ECMWF• Testing
• Tropical Cyclone Monitoring• NRL Monterey
• CIMSS (UW-Madison)
• GPM Satellite Cross-Calibration Work
Dr. Jones and WindSat
• Involvement in early development
• Systems Requirement Review
• Active participation in launch / post-launch activities
• Instrumental in calibration and validation exercises
• Design and analysis of pitch maneuver
• Identification of cold reflector spillover
5
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WindSat Warm Load Anomaly
• PRT measured warm load temperature is not what the radiometer measures
• Details of the problem found in Twarog (2006)
• Correction a function of solar beta angle
6
MHB - IGARSS 2007.
CANISTER DECK (Silver teflon tape)
PRT
18.7
PRT
37
PRT
10.7
Sun reflecting into warm load produces thermal gradients in the warm loadnot a problem during Feb., Mar., Oct. and Nov.worst in late May through mid July
Cold Calibration Intrusions
7
• Space-based RF contamination from geostationary satellites
• 10.7 GHz
• 18.7 GHz
• Lunar contamination occurs with lunar cycle
• 3-4 days in duration
• Centered on full moon
• Statistical detection and correction Moon
Space-Based RFI
Along Scan Variations
• Result of changes in the field of view of the feeds• Power from the Earth scene, CMB, spacecraft, sensor
• Scan dependent spillover and bias corrections• TA = ηT'A + (1 – η) TCMB + β• TA is the antenna temperature
• η is spillover
• TCMB is cold space temperature
• β is a constant bias term
• Changes in cross polarization may also be present• Difficult to correct accurately
• Tp ≈ (1 – a) T'Ap + a(T'Av – T'Ah) where a << 1
• Analysis must consider EIA variations
• Pitch offset = 0.19o and roll offset = -0.14o8
Vicarious Calibration
• Minimum ocean Tb for cold calibration temperature
• Ruf et al. (2000, 2006); McKague et al. (2008, 2009)
• Tropical Forest as hot calibration reference
• Brown and Ruf (2005); Mo (2007)
• Two months of data
• Over 4000 orbits
9
Tropical Forest Mask for 18.7 GHz
Pitch Maneuvers
10
• Similar to maneuver performed with TRMM
• WindSat pitched +/-45o
• Main reflector views cosmic microwave background (CMB)
• Useful for diagnosing azimuthally-dependent radiometer variations
• Isotropic CMB removes EIA dependence
480 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 44, NO. 3, MARCH 2006
Fig. 11. Locus of main beam pointing into space during the positive 45 pitchmaneuver. Also shown are the azimuth blockage ranges for the hot and coldcalibration loads.
Fig. 12. Typical measured Tb (18 GHz), during a pitch maneuver.Forward measurement swath covers azimuth angles from approximately 290to 50 (exact azimuth range is dependent upon individual feeds).
Fig. 13. Ground track for first WindSat pitch maneuver for descendingrev-316 on January 28, 2003. Note that the satellite travels from North Americato the South Pole.
proof-of-concept mission for the polarimetric radiometry tech-nique for measuring oceanic wind vector. The wind directiondependence of the third and fourth Stokes parameters is two
Fig. 14. Typical ground track for the main reflector during the cold-loadmeasurement ( , gay line) and while viewing forward at the right-handswath edge ( , black line). Satellite orbit, rev-2611, is ascending fromsouth to north.
Fig. 15. Radiometer output (rad_counts) during pitch maneuver, rev-316, formain beam forward look (light gray) and cold-sky reflector (dark gray) for37-GHz H-pol. The X axis is spin number (relative time).
orders of magnitude smaller than the vertical and horizontalpolarization signals typically measured by passive microwaveimagers. As such, the design sensitivity analysis resulted insensor noise and absolute accuracy requirements approximately50% tighter than the current SSM/I operational performance.Antenna and receiver polarization purity and horn/antenna/pay-load alignments are significant elements of the accuracy errorbudget. Also, the requirements for radiometric calibrationare especially stringent because this is the first polarimetricradiometer to fly in space and this mission serves as a risk-re-duction pathfinder for the polarimetric channels on the futureNPOESS CMIS instrument; therefore extreme care was madeto provide the purest absolute calibration for the radiometerchannels. In this way, it should be possible to separate in-strumental effects from geophysical effects, which is vital forapplication to other instrument designs such as CMIS.
Authorized licensed use limited to: NRL. Downloaded on June 14,2010 at 14:42:15 UTC from IEEE Xplore. Restrictions apply.
Jones et al. 2006
Along-Scan Bias: Vicarious versus
11
18.7 3rd Stokes, Forest, Vicarious
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JONES et al.: DEEP-SPACE CALIBRATION OF THE WINDSAT RADIOMETER 493
Fig. 34. Differential Tb for orthogonal channels (V-H, P-M, and L-R) during pitch dwell for 18.7 GHz and for eight revs. The X axis is azimuth bin number(2 steps).
Fig. 35. Measured Tb for main reflector forward look during pitch dwell for 23 GHz for V-pol and H-pol for revs: 316, 1948, 2611, and 4607. The X axisis azimuth bin number (2 steps) where number and bin number view to the left side of the satellite subtrack and bin number view tothe right.
Authorized licensed use limited to: NRL. Downloaded on June 14,2010 at 14:42:15 UTC from IEEE Xplore. Restrictions apply.
Jones et al. 2006
WindSat Retrievals
12
• Ocean retrievals
• Three Resolutions
• Low: 50 km x 71 km
• Medium: 35 km x 53 km
• High: 25 km x 35 km
• Near-surface vector winds
• Water vapor
• SST
• Cloud
• Precipitation (GPROF)
• Soil moisture
• Sea ice concentration Parma
WindSat Ocean Retrievals
• Physically-based
• Parameterized forward atmospheric RTM
• Empirically-tuned sea-surface emissivity model
• Optimal estimator
• Minimize cost function
•
• Goodness of fit
•
• Depends on # of channels
• Depends on # of retrieved parameters
13
0 90 180 270 360Relative Wind Direction (degrees)
-0.4
-0.2
0
0.2
0.4
0.6
Dir
ecti
onal
Dep
enden
ce (
K)
T3
T4
0 90 180 270 360Relative Wind Direction (degrees)
-0.4
-0.2
0
0.2
0.4
0.6
Dir
ecti
onal
Dep
enden
ce (
K)
Tv
Th
10.7 GHz at 8 m/s Wind Speed
WindSat Extratropical Observation
14
Surface model tuned for high wind speed retrievals
QuikSCAT0352 UTC12 January 2008
WindSat0245 UTC12 January 2008
WindSat Wind Vectors
15
Low Resolution High Resolution
Another Use for χ2
16
LPQOÍ LUOÍ OÍ JUOÍ JPQOÍ
LUOÍ
LROÍ
OÍ
JROÍ
JUOÍ
OMO OMQ OMS OMU OMW PMO
m\¶\“?q¡†¡\‒|⁄?k\‘›‒\‡›‒„ QOPOOS
P(χ2)0.3
18.7 GHz
10.7 GHz 10.7 GHz
10.7 GHz
Soil Moisture
17
United States
France
Mongolia
Global soil moisture patterns are consistent with climate zones and precipitation climatology
Summary
18
• Consistent calibration across the scan
• No inter-calibration with other instruments
• Absolute calibration with RTM at EDR level
• Investigating Tb stability over mission
• Constant RFI monitoring
• Can mitigate in ocean retrievals
• Produce a number of EDRs
Hurricane FabianHigh Resolution (No 6.8 GHz)
WindSat Related Talks
19
Title: WINDSAT SOIL MOISTURE AND VEGETATION WATER CONTENT OBSERVATIONS ASSOCIATED WITH THE 2003 EUROPEAN HEAT WAVETopic: Land: Soils and Soil MoistureSession: Soil Moisture and Vegetation Characterization Using Microwave ITime: Friday, July 30, 14:55 - 16:00Authors: Li Li, Sonia Seneviratne, Peter W. Gaiser, Gerald Nedoluha
Title: Time Evolution and Spatial Distribution of Ocean-Reflected Radio-Frequency Interference During the WindSat EraTopic: Invited Sessions: Frequency Allocation for Remote Sensing and RFI Mitigation for Microwave RadiometrySession: Frequency Allocation for Remote Sensing and RFI Mitigation for Microwave RadiometryTime: Wednesday, July 28, 13:35 - 15:15Authors: Ian S. Adams, Michael H. Bettenhausen, Peter W. Gaiser, William Johnston
Title: COMPARISON OF VEGETATION WATER CONTENT ESTIMATES FROM WINDSAT AND MODISTopic: Land: Soils and Soil MoistureSession: Remote Sensing of Soil and Vegetation: Applications IITime: Friday, July 30, 09:40 - 10:45Authors: E. Raymond Hunt Jr., Li Li, M. Tugrul Yilmaz, Thomas Jackson
Title: ANTICIPATING THE VIIRS AND MIS SENSORS ABOARD NPOESSTopic: 30th Anniversary: 30th AnniversarySession: Education and Remote Sensing PostersTime: Tuesday, July 27, 14:55 - 16:00Authors: Thomas Lee, Jeffrey Hawkins, Arunas Kuciauskas, Kim Richardson, Michael H. Bettenhausen, Ian S. Adams, Steven D. Miller
WindSat Related Talks
20
Title: CORRECTION ON AMSR-E AND WINDSAT SST FOR LONG TERM TRENDTopic: Sensors and Platforms: Radiometer Instruments and CalibrationSession: AMSR-E IITime: Thursday, July 29, 15:40 - 17:20Authors: Akira Shibata
Title: CHARACTERIZATION OF K-BAND RADIO FREQUENCY INTERFERENCE FROM AMSR-E, WINDSAT AND SSM/ITopic: Sensors and Platforms: Radiometer Instruments and CalibrationSession: Airborne and Spaceborne Measurements of Radio-Frequency InterferenceTime: Wednesday, July 28, 15:40 - 17:20Authors: Darren McKague, John Puckett, Christopher Ruf
Title: WINDSAT RETRIEVAL OF OCEAN SURFACE WIND SPEEDS IN TROPICAL CYCLONESTopic: Student Paper Contest: Student Paper ContestSession: Student Contest IITime: Wednesday, July 28, 10:25 - 12:05Authors: Amanda Mims, Rachael Kroodsma, Christopher Ruf, Darren McKague
Title: INTERSATELLITE CALIBRATION OF MICROWAVE RADIOMETERS FOR THE GLOBAL PRECIPITATION MEASURING MISSIONTopic: Invited Sessions: Microwave scatterometry, radiometery and ocean applications (honoring Dr. W. Linwood Jones)Session: Microwave Scatterometry, Radiometry and Ocean Applications (Honoring Dr. W. Linwood Jones) ITime: Tuesday, July 27, 13:35 - 15:15Authors: Thomas Wilheit
Title: INTERCALIBRATION OF AMSR-E AND WINDSAT BRIGHTNESS TEMPERATURE MEASUREMENTS OVER LAND SCENESTopic: Sensors and Platforms: Radiometer Instruments and CalibrationSession: AMSR-E ITime: Thursday, July 29, 13:35 - 15:15Authors: Thomas Meissner, Frank Wentz
Thank You Dr. Jones!
21