Geoscience Reference
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products (e.g., Reul et al. 2012 ) have been implemented (see a complete description in the
Algorithm Theoretical Basis Document (ATBD) available at http://www.argans.co.uk/
smos/docs/deliverables/ ) . Nevertheless, accuracy of these instantaneous SSS retrievals is
rather low (*0.6-1.7), and space-time averaging of the level 2 products is needed
(so-called level 3 SSS) to decrease the noise level in the retrievals.
Here, we used two types of composite SSS level 3 products generated in laboratories
participating to the Expertise Center of the Centre Aval de Traitement des Donn´es SMOS
(CATDS, http://www.catds.fr ) , which is the French ground segment for the SMOS data.
These products are built either from ESA level 1 products (Reul and Tenerelli 2011 )or
from ESA level 2 products (Boutin et al. 2012b ).
These research products aim at assessing the quality of SMOS operational products
(ESA level 2 and CATDS-OP level 3) and at studying new processing to be implemented
in the future in operational chains. Main characteristics of these products are detailed in
Table 1 . CEC-IFREMER products have been used in Sects. 3 , and 5 , CEC-LOCEAN
products in Sect. 4 .
Overall accuracy of the 10-day composite products at 25-km resolution is on the order
of 0.3 practical salinity scale in the tropical oceans (Reul and Tenerelli 2011 ).
2.2 Ocean Surface Currents
Here, we used the 1/3 resolution global surface current products from Ocean Surface
Current Analyses Real time (OSCAR) (Bonjean and Lagerloef 2002 ; http://www.oscar.
noaa.gov ), directly calculated from satellite altimetry and ocean vector winds.
Table 1
Summary of characteristics of CATDS-CEC SSS level 3 products
CEC-IFREMER
CEC-LOCEAN
SSS retrieval method
SSS retrieved from first Stokes
parameter (Reul and Tenerelli
2011 )
SSS retrieved from polarized Tbs
along dwell lines using an iterative
retrieval (see ESA L2OS ATBD)
Region of the instrument
field of view (FOV)
considered for SSS
retrieval
Alias free field of view only
Alias free field of view (AFFOV) and
extended AFFOV along dwell lines
with at least 130 Tb data samples in
AFFOV (*±300 km from the
swath center)
Tb filtering method
Determined from interorbit
consistency in incidence angles
classes and thresholding
Determined from consistency along
dwell lines as reported in ESA level
2 products
Galactic model
Geometrical optics model
Kirchoff's approx. scattering at 3 m/s
Roughness/foam models
Empirical adjustment of Tb
dependencies to wind speed
Empirical adjustment of parameters in
roughness model and foam coverage
models (Yin et al. 2012 )
Calibration
Single ocean target transformation
(OTT) ? daily 5 9 5
adjustment wrt World Ocean 2001
SSS climatology
Variable OTT (every 2 weeks
synchronized with noise injection
radiometer as defined in ESA
reprocessing)
Average
Simple average
Average weighted by theoretical error
on retrieved SSS and spatial
resolution
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