Introduction Martin et al. JGR, 2014 CAROLS airborne Tbs indicate slightly lower wind influence than predicted by model 1 at high WS In model 1 previous development we empirically derive foam coverage from SMOS Tbs assuming Stogryn 1972 empirical foam emissivity model (fn of frequency and incidence angle). Since that model was developped for freq>13GHz, we review the SMOS foam model 1 (emissivity+coverage)

Introduction SMOS model 1 v6 -ARGO comparisons;

Comparison ARGO- roughness old model 1 & model 3 (Guimbard) in version 623 – May 2011 Colocs +/-5d-+/-50km

Model 1 Model 3

S. Pac (50S-40S) Asc.Desc. Same std whatever the model but various biases (U)

S. Ind. (40S-30S) Asc.Desc.

SPURS

ITCZ

Along track in the FOV (+-20km) and in front of Nadir SMOS ascending Tbs (L1c V620 ): Tbs along track (~ no mixing of polarization) in the Southern Pacific (far from land) from 50°S to 0°N. L2 measurement discrimination (same as for OTT generation except). 15 ascending orbits in May ascending orbits in November 2012 SMOS data used Incidence angles from 0° to 55°

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

Data fitting Wind induced component of emissivity deduced (0-55° in step of 5°) Tb wind =(1-F)Tbrough + F(Tbfoam-Tbflat) 3m/s<U<7m/s a 0 (prior=0.004 – 0.008) 8m/s<U<22m/s Coverage F(U) & emissivity e foam (U) a 0 =0.005 (same as Yin et al., 2012) Spectrum (proportional to Durden and Vesecky wave spectrum) Foam Thickness(U)

e f = m U e fU + m D e fD + m w Foam emissivity upward e downward e reflected transmitted water e Microwave emissivity of sea foam layers with vertically inhomogeneous dielectric properties Thickness Ulaby et al., 1981, 2013, Anguelova and Gaiser, 2013 Atmosphere Water Incoherent foam layer hfhf

Dependence of foam emissivity on foam layer thickness Z for different frequencies Thickness is a key point for the foam emissivity at L band (it varies from 0.35 to close to 1 with thickness varying from 0.01cm to 2cm) In the following, we assume Thickness = fn(U)

L band foam thickness, foam coverage & Void Fraction derived from SMOS multi-angular TBs using a Levenberg & Marquardt minimisation scheme Tbsea(U, θ)= (Tb flat (θ) +Tb rough (U, θ)) (1-F(U)) + F(U) Tb foam (U, θ) Tb rough (U, θ) uses U 3-7m/s, F(U) Tb foam (U, θ) uses U 8-22m/s Thickness(U) (‘effective’) Foam coverage(U) Fitted Void Fraction (percentage of air in a bubble) at the air-foam interface is always around 98%.

Foam emissivity VS wind speed (thickness) Foam emissivity (different U) VS incidence angle

THwind and Tvwind VS wind speed TB model -TB SMOS D: Durden K: Kudryatsev

Summary A new model has been developped based on 2 months of L1 v6 data.

Comparisons with other models