Aquarius´ combined active passive algorithm for ocean surface salinity and wind retrieval

This paper describes the updated Combined Active-Passive (CAP) retrieval algorithm, which uses Aquarius´ brightness temperature and radar backscatter from sea surfaces for simultaneous retrieval of surface salinity and wind. Unlike the algorithm developed by the Remote Sensing System (RSS), the Jet Propulsion Laboratory (JPL) CAP algorithm does not require monthly SSS maps to constrain the salinity retrieval. Furthermore the RSS algorithm fully uses the National Center for Environmental Predictions (NCEP) wind for data correction, while the CAP algorithm uses the NCEP wind only as a loose constraint. The major updates to the CAP algorithm include the galactic reflection correction, Faraday rotation and antenna pattern correction as well as the geophysical model functions (GMF) of wind, wave and rain impacts. Recognizing the limitation of geometric optics scattering, we improve the modeling of the reflection of galactic radiation; the results are improved salinity accuracy and significantly reduced ascending-descending bias in the salinity retrievals. We also describe the updated performance assessment of the scatterometer-only and CAP wind speed products with more than 2 years of data.