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SMOS SSS and wind speed

SMOS SSS and wind speed. J. Boutin, X. Yin, N. Martin. Thanks to ARGANS for their advices for adapting the L2OS processor for our tests!. -Optimization of roughness/foam model -Comparison of new-old ECMWF wind speeds -SSS anomaly in the eastern equatorial Pacific.

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SMOS SSS and wind speed

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  1. SMOS SSS and wind speed • J. Boutin, X. Yin, N. Martin Thanks to ARGANS for their advices for adapting the L2OS processor for our tests! -Optimization of roughness/foam model -Comparison of new-old ECMWF wind speeds -SSS anomaly in the eastern equatorial Pacific

  2. -Optimization of roughness/foam models -Comparison of new-old ECMWF wind speeds -SSS anomaly in the eastern equatorial Pacific

  3. Motivation: SMOS Model 1 - ARGO SSS (3-31 August 2010; asc orbits)versus wind speed (center of orbit) Problem at high wind speed! (Boutin et al., submitted to TGRS, 2011)

  4. Adjustment of some parameters of roughness and foam modeling Roughness:Omnidirectional wave spectrum Durden & Vesecki,1985 : a0?Original publication: a0=0.004; DV2, a0=0.008 Th_30° DV2 Nadir • At 15°C, a 0.1K Tb variation can be generated by : • 0.2pss SSS variation • or • - 0.5m/s wind speed variation ~0.2K/m/s Dinnat et al., IJRS, 2002, Radio Science, 2003 10m equivalent neutral wind speed (m/s) Foam coverage (from Monahan & O'Muircheartaigh 1986): b? c? original publication:b=1.95×10-5, c=2.55 ; ΔT =Tsea-Tair (neglected in this first step study); in first SMOS SSS1 processing, F=0: no foam. Foam emissivity (Stogryn, 1972): assumed to be correct

  5. 8m/s<U<17m/s Foam coverage model b, c Model parameters fitting Wind induced component of emissivity fitted from SMOS data corrected from flat sea emission, atmospheric effects, galactic noise, Faraday rotation Incidence angle (°) 3m/s<U<7m/s Wave spectrum parameter a0 (prior=0.004 – 0.008) (20-55° in step of 5°)

  6. Radiometric accuracy SMOS data used in the fit SMOS Tbs: Tbs along track (~ no mixing of polarization) in the AFFOV (good radiometric accuracy) from 19 ascending orbits in August (low galactic noise) in the South Pacific (far from land) from 50°S to 0°N – Incidence angles from 20° to 55° Incidence angle (°) Along track in the AFFOV 5K 5K 0 0

  7. Wind Speed data • 19 half orbits of SMOS in the southern Pacific. 2 sources of wind speeds considered: SMOS-ECMWF and/or SSMI from RemSS: • ECMWF WS • ECMWF WS with the differences between ECMWF and SSMI WS restricted to be less than 2 ms-1 • SSMI WS colocated at +-0.5h +-50km

  8. Fitted parameters

  9. Comparison of SMOS-foam coverage model with existing parametrizations (all ECMWF-SMOS WS) (ECMWF only if WS consistent with SSM/I) (SSM/I)

  10. X SMOS data +/-1std X X X X X X X X X X X X X X X X X X Pre-launch model 1 New rough/foam model 1

  11. H pol. 20° V pol. 20° SMOS measured and simulated emissivity per ECMWF wind speed classes H & V and various incidence angles in AFFOV H pol. 30° V pol. 30° H pol. 40° V pol. 40° H pol. 50° V pol. 50° H pol. 55° V pol. 55° ECMWF WS ECMWF WS

  12. Monthly averages, Ascending orbits, Pacific Ocean,August 2010 SSS North-South profile, New parametrization for roughness and foam coverage Old model 1 (DV2) Comparisons w.r.t climatology (similar to ARGO analysed map)

  13. Comparison with ARGO SSS 1. The tropical Southern Pacific ocean (20°S10°S- 140°W110°W) far away from continent and island characterized by relative stable moderate wind speed and high SST; mean (standard deviation) of SST and SSS are 24.5 (1.0) °C and 36.2 (0.3) pss 2. The high latitude Southern Pacific ocean (50°S45°S- 180°W100°W) characterized by very variable wind speed and low SST; mean (standard deviation) of SST and SSS are 9,8 (1.8) °C and 34,4 (0.2) pss

  14. Comparison with ARGO measurements August; ascending orbits SMOS SSS retrieved with the pre-launch model 1 SMOS SSS with the new model M1 Less biases than pre-launch model at high wind speed but still large scatter: We trust more retrievals between 3 and 12m/s (=> flag in L2OS processor) in red for the tropical Southern Pacific and in green for the high latitude Southern Pacific

  15. Summary SMOS data evidence that Tb(U) is non linear A reasonnable fit to SMOS data is obtained when introducing a foam coverage parametrization close to Monahan and Muircheartaigh (1986), (this foam coverage may be peculiar to L-band and depends on the foam emissivity model) Parameter for the DV wave spectrum (a0) equal 0.005 (DVx2 replaced by DVx1.25!) New model to be introduced in next release of L2OS processor

  16. -Optimization of roughness/foam models -Comparison of new-old ECMWF wind speeds -SSS anomaly in the eastern equatorial Pacific

  17. Influence of new ECMWF wind speeds Data and Methods 1. L2OS V317 and 5 half orbits in May 2011(only one half orbit shown here as an example)2. New roughness/foam model 1 (Yin et al. submitted to TGRS 2011, presented before); 1.5 m/s error on wind components3. Only grid points in 50S-0S within ±300km of the swath center and flagged as good quality have been used

  18. Old and new ECMWF wind speed Wind speed (new) (m/s) Wind speed (new-old) (m/s) Orbit: 20110512T152208_20110512T161609

  19. ECMWF wind speed (new-old) Retrieved wind speed (new –old) Std=0.51m/s Std=0.72m/s SMOS retrieval not able to correct for whole large WS errors (otherwise (new-old) retrieved WS=0)) but correct part of them: over 5 orbits: std(new-old)retrieved WS / std(new-old) ECMWF WS =0.7 Orbit: 20110512T152208_20110512T161609

  20. SSS retri(new-old), med = -0.033, std=0.25 WS retri(new-old), med = -0.09 New ECMWF WS leads to changes in SSS; improvement in retrieved SSS still needs to be assessed by comparison with ground truth (5 orbits, not enough because of high noise). Orbit: 20110512T152208_20110512T161609

  21. -Optimization of roughness/foam models -Comparison of new-old ECMWF wind speeds -SSS anomaly in the eastern equatorial Pacific

  22. From N. Reul talk at EGU 2011 El-Nina SSS anomalies detected by SMOS in August Systematic SMOS Error There: Roughness ? SST ?

  23. From Boutin, Lorant et al. :SMOS SSS > ARGO SSS together with SSMI WS<SMOS retrieved WS < ECMWF WS SSSsmos-SSSargo : 1.578 psu WSssmi : 1.8 m/s WSecmwf : 6.85 m/s WSsmos: 4.23m/s (time difference : -0.306 h) ECMWF WS SSMI WS

  24. 1 month (170 orbits in Pacific Ocean) SMOS SSS <300km ECMWF-SMOS WS Equator SSS anomaly corresponds to a SMOS retrieved wind speed lower than ECMWF (August, ascending orbits, S. Pacific, new direct rough/foam model)

  25. Monthly SMOS SSS (center swath +/-250km) ARGO/ISAS SMOS, without retrieving WS SMOS, with WS retrieved

  26. Monthly wind speed Radiometric wind speeds lower than ECMWF in that region caracterized with large surface currents SMOS retrieved WS SSMI radiometric WS (RSS monthly product) (SSMI 19/22/37 GHz) ECMWF

  27. 2-31st August SSS latitudinal profiles (asc. orbits only) Border track Outside +/-300km Center track +/-300km SSSsmos-climatology Wind Pb Why? Could it be an artefact of LO cal? center border

  28. LO cal latitudinal distribution superimposed on SSS latitudinal biases (from Guillermo) 1psu -1psu

  29. Summary SMOS data evidence that Tb(U) is non linear => new model including foam SMOS retrieved wind speed within new and old ECMWF wind speeds (the retrieval corrects for part of the ECMWF inaccuracies) SMOS retrieved wind speed is partly (but not entirely) corrected for inconsistencies between ECMWF wind speeds and radiometric wind speeds => it remains flaws in SMOS SSS when large WS discrepancies => when looking at SMOS SSS anomalies; check first the consistency between ECMWF and SMOS retrieved WS! Need to find a tradeoff between giving more freedom to the WS in the retrieval and not degrade SSS Possible artifacts linked to LO calibration frequency needs to be better looked at

  30. How to deconvolve SMOS data in order to estimate bistatic coefficients for galactic noise correction? Limits of feasibility? Error estimates? Jean-Luc Vergely (ACRI-ST) Jacqueline Boutin (LOCEAN) Thanks to N. Reul, J. Tenerelli for helpful discussions QWG 5

  31. The Galactic noise problem Problem: At present none of our theoretical models able to simulate it correctly: Tenerelli & Reul, 2010 Up to now, empirical determination hampered by problems of SMOS biases, uncertainty in roughnes/foam models etc… but this is improving QWG 5

  32. Bistatic coefficient estimation The galactic noise signal seen in SMOS data comes from sky emission convoluted with bistatic coefficients that depend on the wind speed (the stronger the wind speed, the larger area of the sky significantly affects the scattered galactic noise signal with a lower influence of the specular direction). Development of numerical simulations for studying : • Feasibility of estimating bistatic coefficients from SMOS data. • Determination of the error on the bistatic coefficient estimator. 10/11-04-2011 QWG 5 Progress meeting

  33. Bistatic coefficients estimated from SMOS simulated data: a first try Retrieved bistatic coefficient Assumptions : Incident galactic noise is not polarized. WEF applied before reflection Bistatic retrieval : Non parametric Bayesian approach with a priori correlation length. Deconvolution with strong a priori knowledge Modeled SMOS data using new bistatic coefficients SMOS noisy simulated data (averaged) Finding SMOS specular measurements with same relative geometry and WS SMOS simulated data no noise assuming bistatic coeff. Residual TBs

  34. Summary • We presented the methodology we are developping for estimating scattered galactic noise and its associated error - To identify situations well sampled by SMOS data for tuning theoretical model and for quantifying errors • Preliminary tests based on simulated data indicate that it will better work at low-moderate wind speeds (deconvolution over a smaller region; situations often sampled) • Need for L1 reprocessed data including correct sun correction (otherwise our estimates will be biased by sun!) • Only a piece of studies about galactic noise as it probably won’t cover all the situations, but it will add constraints! • More using SMOS data at future QWG! • Given our present knowledge, we recommend a careful flagging for reprocessing QWG 5

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