Improved Sea Surface Salinity Retrievals Using Ancillary Data for Aquarius Ocean Roughness Correction
[03-Dec-2012] Jones, L., Hejazin, Y., and Rabollii, M.
Presented at the 2012 AGU Fall Meeting
The Aquarius/SAC-D sea surface salinity (SSS) measurement mission was launched into polar orbit during the summer of 2011. The prime sensor is a combined L-band radiometer/scatterometer developed jointly by NASA Goddard Space Flight Center and the Jet Propulsion Laboratory, which derives SSS from ocean surface brightness temperature (Tb) measurements. This paper deals with a method of improving AQ SSS by making a making an ocean roughness brightness temperature correction (ΔTbr). The ΔTbr is derived using several ancillary data sources of surface wind measurements, namely; NOAA numerical weather model - Global Data Assimilation System (GDAS), WindSat ocean vector wind, and the CONAE Microwave Radiometer (MWR).
The basis of the correction is the excess (warming) brightness temperature that is produced when the ocean is roughened by the surface wind. We model the increase in L-band Tb as a function of wind speed and direction relative to the antenna azimuth look direction. Our radiative transfer model by El-Nimri  has been tuned to actual AQ ocean surface Tb's with corresponding surface wind vector. Using this ocean emissivity model and the ancillary wind vector, we derive the roughness correction, ΔTbr, which is applied to the AQ measured ocean surface Tb before retrieving SSS.
Finally the effect of ΔTbr is evaluated by computing the difference between the HYCOM ocean salinity model and the AQ retrievals. These differences are cross correlated with the ancillary surface wind vector to assess the effectiveness of the roughness correction. Finally, we compare our ΔTbr with the AQ scatterometer derived ?Tbr. We compare the similarities and differenced versus the ancillary surface wind speed.