The following lists important SMAP version updates:
SMAP V3.0 uses the geophysical model function (GMF) from Aquarius V5.0 release adapted to SMAP V4.0 (Meissner et al. 2017, 2018). Cross-Calibrated Multi-Platform (CCMP) product is used for near-real time ancillary wind speed and wind direction. V3.0 includes the NASA Global Precipitation Measurement (GPM) Integrated Multi-Satellite Retrievals for GPM (IMERG) rain rate for the atmospheric liquid cloud water correction and rain flags.
The most important improvement in V4.0 is the land correction. The spatial resolution of the land tables is 1/2° in V3.0 and has been increased to 1/8° in V4.0. The land surface TB was based on a land surface emission model in V3.0 but is based on a monthly climatology of SMAP land TB measurements in V4.0. In V3.0, the sea-ice mask was from NCEP and is replaced with RSS AMSR-2 sea-ice maps in V4.0. The V4.0 salinity retrieval algorithm is using 40-km spatial Backus Gilbert Optimum Interpolation (OI). From the 40-km product, the smoothed 70-km product is derived using simple next-neighbor averaging.
The sea-ice flagging and masking in V5.0 ingests 8-day averaged AMSR-2 TB measurements directly, rather than an external, derived ancillary sea-ice concentration. In V5.0, salinity fields are classified into different sea-ice zones to show the levels of sea-ice contamination in the antenna field of view based on nearest neighbor and next to nearest neighbors of observations that are flagged as sea-ice contaminated. Side-lope correction for sea-ice contamination is applied to the measured SMAP TB before salinity is retrieved.