The version 3.0 SMAP-SSS, level 2C product contains the third release of the validated sea surface salinity orbital/swath data from the NASA Soil Moisture Active Passive (SMAP) observatory, and is produced operationally by Remote Sensing Systems (RSS). Enhancements with this release include: Use of the version 4 L1B SMAP RFI filtered antenna temperatures; Implementation of the geophysical model function from Aquarius version 5 adapted to SMAP; Use of the near real time CCMP wind speed and direction data as ancillary input, and inclusion of IMERG rain rate for the atmospheric liquid cloud water correction and rain flagging; Improved computation of antenna weighted land fraction gland and enhanced correction for land radiation intrusion from antenna sidelobes; Improved SMAP mesh antenna emissivity settings with empirical adjustments to the JPL thermal model. Users should note that significant degradation in the performance is observed if the gain weighted land fraction gland exceeds 1 percent. Because of that, observations with gland greater than 0.8 percent are not used in the Level 3 processing. The SMAP-SSS L2C product includes data for a range of parameters: derived sea surface salinity (SSS), brightness temperatures for each radiometer polarization, antenna temperatures, collocated wind speed, data and ancillary reference surface salinity data from HYCOM, rain rate, quality flags, and navigation data. Each data file covers one 98-minute orbit (15 files per day). Data begins on April 1,2015 and is ongoing. Observations are global in extent and provided at a 0.25 degree x 0.25 degree grid with an approximate spatial feature resolution of 40 km. Note that for most open ocean applications, the related 70-km V3.0 products are the best to use as they have significantly lower noise than the 40-km products.

The SMAP satellite is in a near-polar orbit at an inclination of 98 degrees and an altitude of 685 km. It has an ascending node time of 6 pm and is sun-synchronous. With its 1000km swath, SMAP achieves global coverage in approximately 3 days, but has an exact orbit repeat cycle of 8 days. On board Instruments include a highly sensitive L-band radiometer operating at 1.41GHz and an L-band 1.26GHz radar sensor providing complementary active and passive sensing capabilities. Malfunction of the SMAP scatterometer on 7 July, 2015, has necessitated the use of collocated wind speed, primarily from WindSat, for the surface roughness correction required for the surface salinity retrieval.