SMOS+ polarimetry : Stokes 3

Jean-Luc Vergely (ACRI-ST)Philippe Waldteufel (ACRI-ST)

Eric Anterrieu (IRAP)Ignasi Corbella (UPC)

Frédéric Rouffi (ACRI-ST)

Introduction

Principal aims of SMOS+ polarimetry study :in reponse to ESA ITT ref. ESRIN/AO/1-6704/11/I-AM

1/ Which kind of information can we extract from St3 and St4 SMOS data ?

2/ Is it possible to discriminate between physical signal and instrumental contributions ?

3/ How can we use St3 and St4 to improve the calibration or to help to better understand the instrument ?

Stokes 3 issues

1/ Stokes 3 is sensitive to TEC. So far however, no coherent TEC has been extracted from SMOS Stokes 3.

2/ Is it possible to separate St3 calibration (OTT correction or other) and TEC estimation ?

Sensitivity of St3 and other polarizations to TEC

TB sensitivity to TEC depends on :

-location on the FOV

-latitudinal position on the orbit

-longitude

-ascending/descending

=> Using descending orbits for high TEC contamination.

Sensitivity of St3 to TEC : location on FOV

dTB/dTEC, 20° latitude south dTB/dTEC, 25° latitude north

Low TEC sensitivity

High TEC sensitivity

Descending orbit

St3 St3TX TX

TYTY

Sensitivity to TEC : latitudinal position

Pacific descending orbits

No possibility to retrieve TEC here !

(L.O.S perp. to magnetic field)

St3 is the most sensitive to

TEC

Sensitivity of St3 to TEC : descending orbits

Pacific descending orbits

No possibility to retrieve TEC

but good for (descending) OTT estimation !

Sensitivity of St3 to TEC : ascending orbits

Pacific ascending orbits

No possibility to retrieve TEC

but good for ascending OTT estimation !

Sensitivity of St3 to TEC

If parts of the orbit or of the FOV with dTB/dTEC close to 0 are used in order to derive TEC:

dTEC/dTB -> infinityDelta TEC = dTEC/dTB * Delta TB => explose

If moreover OTT on ST3 is biased:

Delta TEC = dTEC/dTB * (Delta TB + OTTbias) => explose

Use only parts of the FOV with dTB/dTEC significantly different from 0 : that is, top of the ST3 FOV

But in addition reliable OTT (St3) are required.

Next : TEC profile is derived enforcing latitude independent OTT

Land contamination

Shifted "front"L1c TEC problem

Reprocessing orbits 20100801

Derived versus L1c TEC(descending orbits)

TEC & OTT are derived simultaneously

For reliable OTT

estimation

TEC insensitive region. Good for OTT !!

Derived vs L1c TEC: descending orbits

Reprocessing orbits 20100801

L1C TEC

SMOS TEC from ST3

Derived TEC

"Front"=steep lat variation : positions and amplitudes

TEC from IRI

Derived vs L1c TEC: descending orbits, L1c 5XX consolidated TEC

New reprocessing orbits 20101102

L1c TEC problem

TEC insensitive region

________ ≈ 1000 kml, distance between subsat & top of FOV

Shifted "front"

X_swath TEC detection from St3

TEC obtained from St3 front FOV between -0.3<xi<0.3 on 6 xi positions

=> GOOD COHERENCE between different xi positions !!

X_swath TEC detection (ascending)

TEC obtained from St3 front FOV between -0.3<xi<0.3 on 6 xi positions

=> GOOD COHERENCE between different xi positions but some oscillations

OTT estimation : ascending/descending

OTT obtained from St3 front FOV between -0.3<xi<0.3 on 6 xi positions

Classical OTT close to the new one in ascending.

New OTTs are similar in ascending/descending

DESCENDING ORBITS ASCENDING ORBITS

ξ ξ

X_swath TEC detection from TX-TYTEC obtained from TX-TY front FOV between -0.3<xi<0.3 on 6 xi positions

=> Central xi gives results closer to TEC L1c : because of TB sensitivity to TEC.

Same « front » shift than with ST3

Softer response expected because σ_noise (TX-TY) larger than σ_noise St3

TX-TY sensitivity to TEC (front of the FOV)

OTT estimation : ascending/descending

OTT obtained from TX-TY front FOV between -0.3<xi<0.3 on 7 xi positions

DESCENDING ORBITS ASCENDING ORBITS

ξ ξ

As expected : no TEC influence at ξ=0

Too much dispersion ?

ξ

X_swath TEC detection from TX-TY in eta =-0.2TEC obtained from TX-TY between -0.55<xi<0.55 on 15 xi positions.

Wings of the FOV seem give coherent results with central part of the FOV

« Fronts » not at the same place because eta close to the middle of the FOV (not in front of the FOV)Smaller shifts

X_swath TEC detection from TX-TY in eta =-0.2

Where is realy the information ?OTT at eta=-0.2

Conclusions1/ SMOS ST3 is not garbage !! SMOS ST3 carries TEC information: hence possibility to compute TEC from SMOS ST3.

Estimation of TEC from SMOS ST3 is possible only in some parts of the FOV and some part of the orbit.

Since a correct TEC estimation depends on OTT which depends on TEC… TEC and OTT have to be derived together with OTT set in latitude zones where TBs is not sensitive to TEC. Special care has to be taken for descending orbits.

2/ TEC estimation from SMOS ST3 shows that:

-L1c TEC is overestimated (even the consolidated TEC)-L1c TEC "front" is shifted in comparison with SMOS TEC.

Problem of considering constant TEC on the FOV ? SMOS SELF CONSISTENCY done using TX-TYPossible future impact on TEC management ?