The following lists important SMAP version updates:
V3.0:
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.
V4.0:
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.
V5.0:
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.