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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. - PowerPoint PPT Presentation
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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
100.225log ( /2)23 *
0*
1.25( )
kku
S k a kg
Roughness:Omnidirectional wave spectrum Durden & Vesecki,1985 :
Foam coverage (from Monahan & O'Muircheartaigh 1986): 10 exp( 0.0861 )cF bU T
a0? Original publication: a0=0.004; DV2, a0=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 = Tbatm↑ + Rsea (Tbatm↓ + Tbsky) exp(-atm) + Tbsea exp(-atm)
Ocean
Atmosphere
Tbsea= (Tbflat+Tbrough) (1-F) + F Tbfoam
esea derived from SMOS Tbs after correcting for all other effects
Tbsea=esea SST
Incidence angle (°)Radiometric accuracy Along track in the AFFOV
0
5K
0
5K
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 237501 samples in H polarization and 238469 in V polarization collocated with ECMWF WS in range of 3-17ms-1.
2. 56% of the ECMWF wind speeds (136861 samples in H polarization and 137471 in V polarization) have been collocated with SSMI WS in range of 3-17 ms-1 : +-0.5h +-50km
3. 126662 samples in H polarization and 127191 in V polarization, when the differences between ECMWF and SSMI WS were restricted to be less than 2 ms-1
3m/s<U<7m/sa0 (prior=0.004 – 0.008)
8m/s<U<17m/sb, 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 (°)
a0 b c
M1 0.0050 2.42×10-8 4.86
M2 0.0062 2.20×10-9 5.67
M3 0.0070 2.90×10-9 5.51
M1 M2
M3
ECMWF ECMWF+SSMI
SSMI ECMWF
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 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 0.004• 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 PacificLatitude 50S-40S 20S-10SLongitude 180W-100W 140W-110WSST (°C) 9.8 24.5σSST (°C) 1.8 1.0SSS (pss) 34.4 36.2σSSS (pss) 0.2 0.3
pre-launch model 1Wind speed (ms-1) 3-12 12-20 3-12No. of collocations 11714 4060 4556mean(SSSsmos-SSSargo) (pss) 0.08499 -0.89729 0.08477σ (SSSsmos-SSSargo) (pss) 1.06832 1.37645 0.62445median(SSSsmos-SSSargo) (pss) 0.1 -0.82515 0.0905
New model M1No. of collocations 11718 4150 4551mean(SSSsmos-SSSargo) (pss) -0.04846 -0.40917 -0.06231σ (SSSsmos-SSSargo) (pss) 1.0703 1.50764 0.63529median(SSSsmos-SSSargo) (pss) -0.0268 -0.5132 -0.055
Statistics of SMOS SSS collocated with ARGO at +/-5days and +/-50km during August ascending passes