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

!"#$

!" #"" #!" $"" $!" %"" %!" &""

##'##'$

()#"& *+,-.).-/01234),5-)4*23

!" #"" #!" $"" $!" %"" %!" &""

$66"

$7""

" !" #"" #!" $"" $!" %"" %!" &""$68"$69"$66"

" !" #"" #!" $"" $!" %"" %!" &""$68"$69"$66"

" !" #"" #!" $"" $!" %"" %!" &""$68"$69"$66"

:0;<+.0/),5-),0=)<0>3?))!"#$@))))%A&A'):23B)*>*C)+.0/)B>--,B=0,@))))()**+(,-+

!"#$%&$'"$(%)*+$'%,-'#)."/)+"-0%1)($234%35%67/%829-.

:)"0%;$*+'

1-.<%=-)<23

1-.<%=-)<2>

1-.<%=-)<2?

1-.<%=-)<2@&A$$+2(9-+

BC$)0 =)0< BC$)0

!"#$

!" #"" #!" $"" $!" %"" %!" &""

##'##'$

()#"& *+,-.).-/01234),5-)4*23

!" #"" #!" $"" $!" %"" %!" &""

$66"

$7""

" !" #"" #!" $"" $!" %"" %!" &""$68"$69"$66"

" !" #"" #!" $"" $!" %"" %!" &""$68"$69"$66"

" !" #"" #!" $"" $!" %"" %!" &""$68"$69"$66"

:0;<+.0/),5-),0=)<0>3?))!"#$@))))%A&A'):23B)*>*C)+.0/)B>--,B=0,@))))()**+(,-+

!"#$%&$'"$(%)*+$'%,-'#)."/)+"-0%1)($234%35%67/%829-.

:)"0%;$*+'

1-.<%=-)<23

1-.<%=-)<2>

1-.<%=-)<2?

1-.<%=-)<2@&A$$+2(9-+

BC$)0 =)0< BC$)0

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

! "!! #!! $!! %!! &!! '!! (!!)*+,-./0121/,

3"4!

3!4&

!4!

!4&

"4!

56-3-53-789

:0*;,<1,=>;0*;,<1,=

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