SMOS L2 OS ATBD - ARGANS

79
ICM-CSIC
LOCEAN/SA/CETP
IFREMER
SMOS L2 OS
Algorithm Theoretical
Baseline Document
Doc: SO-TN-ARG-GS-0007
Issue: 3 Rev: 9
Date: 25 January 2013
Page: 79
Finally, it should be noted, as discussed in the section describing the theoretical model, that
there may be a dependence of the roughness emission on relative angle between emission
direction and wind direction, but we have not been able to see a consistent azimuthal signal in
the SMOS data as of this writing, and so we current set all azimuthal harmonic coefficients to
zero identically.
4.3.2.2. Quality control and diagnostics
As explained in section 4.3.3 below, the SSA/SPM model is not expected to provide correct
results for wind seas generated by winds less than about 2 m/s and larger than 15 m/s . This
corresponds roughly to wind friction velocity u* less than 0.6 cm/s and larger than 0.5 m/s.
The model can be applied as it is at launch for conditions out of this range however, we
expect that the CAL/VAL activities will provide after commissioning phase a variability
estimate at low winds and a residual foam impact at high winds which will be used to
correctly tune the model.
4.3.2.3. Exception handling
There is no particular exception handling in the mathematical algorithm except if the
following auxiliary data are not provided by the processor or exceed the ranges anticipated:
the neutral equaivalent wind speed [m/s], (which can be estimated fromthe wind
speed magnitude at 10 meter height, the roughness length, and the auxiliary parameter
“Coefficient of drag with waves Cd “defined by : u*= Cd U10
)
the inverse wave age parameter for the wind sea (which can be deduced from
2U
10
estimates of both U 10 and the mean period of wind waves Tp: ),
gT
the incidence angles i at SMOS pixel,
the sea surface temperature Ts,
the prior sea surface salinity SSS, and,
the azimuth angle at SMOS pixel relative to wind direction i .
If one of the prior values of the retrieved geophysical parameters is out of the LUT range, or
if any retrieved geophysical parameter goes out of LUT range during the retrieval, different
flags (Fg_OoR_Rough_dim1, Fg_OoR_Rough_dim2, Fg_OoR_Rough_dim3,
Fg_OoR_Rough_dim4, Fg_OoR_Rough_dim5) are raised. No extrapolation is done and the
boundary value is taken.
4.3.3. Assumption and limitations
As discussed above, the empirical model described above is expected to fail in strong storm
and frontal conditions (strong wave-wave, wave-current or wind-wave interaction
conditions). Furthermore, we do not expect the model to perform well in presence of either
strong swells, strong currents, very small and unsteady winds where the link between surface
p