FR1.L10.2: CALIBRATION OF LOCALIZATION BIASES FOR SMOS

IGARSS 2010 – 25/30 july 2010, Honolulu, HI, USA

Calibration of localization biases for SMOS

François Cabot1, Yann Kerr1, Philippe Richaume1 and Philippe Waldteufel2

(1) CESBIO, 18, Av E Belin 31401 TOULOUSE CEDEX 9 FRANCE(2) IPSL/SA, 91371 Verrières le Buisson, FRANCE


Outline

System level performances as assessed during commissioningGeolocation biases assessment – Best Fit Plane calibration

although higher bias than expected, calibration has been achieved up to required accuracy

Geolocation accuracy – impact at soil moisture levelpreliminary assessment shows we are moving in the right direction, but thorough cal/val results will be needed for final analysis

Equivalent Array Factor – spatial resolution confirmationIn close agreement with expectations, and validated making use of RFI

Radiometric accuracy verification for Land scenesConsistent with theory, and used as such for soil moisture retrieval

Absolute accuracy of brigthness temperaturesDome C results extremely promising, finer analysis still needed.


Geolocation assessment

• Challenging requirement wrt SMOS moderate resolution: 400m rms.

• Method developed and validated before flight with simulated data

• Simple model fit across sharp transition gives access to shift assessment.

• Madagascar coastline selected: long linear coastline.• Spin-off: assessment of synthetic antenna pattern

• Additional checking making use of Earth Horizon crossing the field of view during external calibration manoeuvre.


Madagascar Coastline access


Model fitting results

Pre launch simulation


Ascending - Descending

• Alternate passes are used to constrain geolocation matrix.

• Depending on the position of the coast within the swath, this constrain can change.


Temporal stability

• Rmse on bias assessment is down to 600m.

• No clear temporal evolution being seen on first 2 months of data.

• At end of IOCP, only noticeable trend is on roll, but uncertainty on this trend still high

blue: ascending, red: descending


Earth Horizon• Crossing the fov, very sharp contrast

• Must be used with high rate STR data

• Only over ocean usable: 10 ECM analysed

• Proved more noisy than Madagascar, probably due to limb

• Average pitch bias: -0.0809°


Geolocation summary

• 5 months of data have been used, 49 overpasses• Roll and pitch biases estimated:

– Roll 0.1406– Pitch -0.0736

• Higher biases than expected from satellite budgets– After correction, residual shift down to 221m/388m

(asc/desc) with 319m standard deviation.

• Some issues have been sorted out.– Snapshot datation is middle of integration time– Quaternions are interpolated rather than propagated

Earth horizon crossing during external manoeuvres gives consistent pitch bias assessment.


Geolocation spin-off: ground resolution

Instrumental model used for geolocation assessment includes Blackman rmax parameter.

Retrieved parameter compares well with theoretical resolution, as computed at L1C:

Retrievals proved to be very stable with time.

(km) rmax

std(rmax)

Semi axis (-3dB)

Semi axis in L1C

Ascending

46.7 3.1 18.9 22.0

Descending

45.6 2.0 18.4 19.2


Ground resolution from RFI sourcesMadagascar results can be cross validated making use of

RFI (assumed to be point sources)

A1 (km)

A2(km)

From L1C

45.6 24.8

36.5 23.1

From RFI source

43.5 22

31.5 25


Geolocation impact on Soil Moisture

Same product processed with/without biases correction

Brightness temperature impact less than 3K

SM impact low on average

Coastal zones and high surface variations show higher impacts

Overall statistics suggest better retrieval. Finer analysis over anchor sites still on-going.

Mialon A., 2010


Antarctica around Dome Concordia

• Antarctic plateau around Dome C appears a very good candidate for stability monitoring and across fov consistency check


System level performances

• Average brightness temperature over Antarctic Plateau


System level performances

• Noise level consistent with expectations

pre launch simulations


Antarctica around Dome Concordia

Dome C only, Hallikainen model (one layer, Tsnow=-54)

Tv Domex-2 operative 2009

Th Domex-2 operative 2009

Th Domex-2 Initial 2009

Tv Domex-2 Initial 2009

Tv domex2010

th domex2010

DomeX data, G. Macelloni


Summary

System level performances as assessed during commissioningGeolocation biases assessment – Best Fit Plane calibration

although higher bias than expected, calibration has been achieved up to required accuracy

Geolocation accuracy – impact at soil moisture levelpreliminary assessment shows we are moving in the right direction, but thorough cal/val results will be needed for final analysis. Long-term trends will be monitored.

Equivalent Array Factor – spatial resolution confirmationIn close agreement with expectations, and validated making use of RFI

Radiometric accuracy verification for Land scenesConsistent with theory, and used as such for soil moisture retrieval

Absolute accuracy of brightness temperaturesDome C results extremely promising, finer analysis still needed.

Documents

FR1.L10.2: CALIBRATION OF LOCALIZATION BIASES FOR SMOS