Optimization of L-band sea surface emissivity models deduced from SMOS data X. Yin (1), J. Boutin (1), N. Martin (1), P. Spurgeon (2) (1) LOCEAN, Paris, France (2) ARGANS, Plymouth, UK Two scale + foam

Adjustment of some parameters of roughness and foam modeling Roughness: Omnidirectional wave spectrum Durden & Vesecki,1985 : Foam coverage (from Monahan & O'Muircheartaigh 1986): a 0 ? Original publication: a 0 =0.004; DV2, a 0 =0.008 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 ~0.2K/m/s Dinnat et al., IJRS, 2002, Radio Science, 2003 At 15°C, a 0.1K Tb variation can be generated by : -0.2pss SSS variation or - 0.5m/s wind speed variation 10m equivalent neutral wind speed (m/s) Nadir Th_30° DV2

Modeling of SMOS Tbs Tb = Tb atm ↑ + R sea (Tb atm ↓ + Tb sky ) exp(-  atm ) + Tb sea exp(-  atm ) Ocean Atmosphere Tb sea = (Tb flat +Tb rough ) (1-F) + F Tb foam e sea derived from SMOS Tbs after correcting for all other effects Tb sea =e sea SST

Incidence angle (°)Radiometric accuracy Along track in the AFFOV 0 5K 0 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° SMOS data used in the fit

Three different sets of wind induced components deduced from SMOS 1.There are totally samples in H polarization and in V polarization collocated with ECMWF WS in range of 3-17ms % of the ECMWF wind speeds ( samples in H polarization and in V polarization) have been collocated with SSMI WS in range of 3-17 ms -1 : +-0.5h +-50km samples in H polarization and in V polarization, when the differences between ECMWF and SSMI WS were restricted to be less than 2 ms -1

3m/s<U<7m/s a 0 (prior=0.004 – 0.008) 8m/s<U<17m/s b, c Data fitting Wind induced component of emissivity deduced Er_SMOS (θi, p, ws)= Eres (θi, p) + Espectrum(a0; θi, p, ws) (20-55° in step of 5°) Incidence angle (°)

a0a0 bc M × M × M ×

M1M1 M2 M3 ECMWF ECMWF+SSMI SSMIECMWF

Results in AFFOV H pol. 20 ° V pol. 20 ° 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

Results in EAFFOV ? H pol. 0 ° V pol. 0 ° V pol. 10 ° V pol. 20 °

Comparisons w.r.t WOA05 Old model 1 (DV2) New parametrization for roughness and foam coverage Monthly averages, Pacific Ocean, August 2010 SSS North-South profile,

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

SMOS SSS retrieved with the pre-launch model 1 SMOS SSS with the new model M1 in red for the tropical Southern Pacific and in green for the high latitude Southern Pacific

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 wave spectrum (a0) slightly higher than Preliminary validation shows improvement in mean retrieved SSS A larger set of SMOS data should be used for validating and/or improving model Study the quality of SSS retrieved at high wind speed when putting a larger error on ECMWF wind speed. Check SMOS measurements taken in the EAFFOV

Latitudinal drift ? EH_SMOS - EH_Model, 0deg EV_SMOS - EV_Model, 0deg

Zone Southern Pacific Latitude 50S-40S20S-10S Longitude 180W-100W140W-110W SST (°C) σSST (°C) SSS (pss) σSSS (pss) pre-launch model 1 Wind speed (ms -1 ) No. of collocations mean(SSS smos -SSS argo ) (pss) σ (SSSsmos-SSSargo) (pss) median(SSS smos -SSS argo ) (pss) New model M1 No. of collocations mean(SSS smos -SSS argo ) (pss) σ (SSSsmos-SSSargo) (pss) median(SSS smos -SSS argo ) (pss) Statistics of SMOS SSS collocated with ARGO at +/-5days and +/-50km during August ascending passes