SMAP Salinity

V2.0 Validated Release

SMAP sea surface salinity (SSS) V2.0 validated release data are available from Remote Sensing Systems. The near-polar orbit of SMAP allows for complete global coverage of the oceans in 3 days with a repeat cycle of 8 days.  The RSS SMAP SSS V2.0 validated release contains 3 products:

  1. Level 2 
  • time
  • S/C orbital information
  • pointing information
  • antenna temperatures
  • brightness temperatures
  • calibration data
    • physical temperature of mesh antenna
    • emissivity of mesh antenna
    • characterization of calibration drift
  • corrections for
    • reflector emissivity
    • calibration drift
    • galaxy
    • sun
    • moon
    • cold space
    • land intrusion
    • ionosphere
    • atmosphere
    • surface roughness
  • SMAP sea surface salinity
  • Quality Control Flag indicating degradation
  • ancillary fields
    • SST
    • solar flux
    • wind speed
    • atmospheric correction (TRAN, TBUP, TBDW)
    • surface rain rate 
    • land fraction
    • sea ice fraction
  • reference salinity from HYCOM
  • expected TA (calculated from RTM using HYCOM reference salinity)
  1. Level 3 8-day running averages.
  2. Level 3 monthly averages.

The Level 3 files contain:

  • Number of observations in each L3 grid cell
  • SMAP sea surface salinity
  • reference sea surface salinity from HYCOM
  • ancillary land fraction
  • ancillary sea ice fraction
  • ancillary sea surface temperature

All files are in netCDF4 format and are CF compliant. For details about the RSS SMAP SSS V2.0 validated release (release notes, file and data formats, description of the algorithm, ATBD, validation), consult the V2.0 Release Notes.


Updates from the V1.0 (BETA) release:

  1. Antenna Pattern Correction (APC): The spillover, or equivalently the matrix element AII in the APC matrix, was increased from 1.0929 (V1.0) to 1.1080 (V2.0).
  2. The along-scan bias correction in V1.0 has been removed.
  3. The emissivity of the mesh antenna was set to 0.01 for both V-pol and H-pol polarizations.
  4. JPL has updated their thermal model for the physical temperature of the reflector. 
  5. In addition, an empirical adjustment to the thermal model has been introduced in order to mitigate observed zonal and seasonal biases in V1.0. 
  6. The correction for the reflected galaxy has been updated based on the SMAP fore – aft look analysis.
  7. The land correction has been tuned to mitigate salty biases around the continents in the S hemisphere (E coast of S America, Australia) that were prevalent in V1.0.
  8. The ancillary SST for V2.0 is taken from the Canadian Meteorological Center CMC.  V1.0 had used Reynolds OI SST as ancillary SST input.
  9. Level 2C (L2C) data files including all intermediate steps from TA to SSS are released including a L2 Q/C (quality control) flag. 
  10. The Level 3 data include averages for land fraction, sea ice fraction and SST.


SMAP is different than Aquarius

Both SMAP and Aquarius are L-band radiometers capable of measuring sea surface salinity.  However, there are important differences as listed below:

1.   SMAP observes the Earth in nearly full 360-degree scans, whereas Aquarius looked at the Earth at three fixed angles.  This design difference results in a 1000 km wide SMAP swath as compared to the narrow 350 km Aquarius swath. The wider SMAP swath results in greater Earth coverage in less time.  We also believe that the ability of SMAP to observe the same location at the Earth surface from different directions and viewing angles helps to eliminate various spurious signals that are a function of viewing direction (an-isotropic signatures), such as signals from the sun, galaxy, moon, or the Earth's ionosphere.

2.   SMAP observations have a footprint size of 40 km which is a higher resolution than the 100 - 150 km footprints of Aquarius.  As a consequence, the SMAP data are noisier than Aquarius, but the noise can be reduced by temporal averaging the data over days or weeks. 


How to cite the RSS SMAP salinity data

As a condition of using these data, we require you to use the following citation:

Meissner, T. and F. J. Wentz, 2016:  Remote Sensing Systems SMAP Ocean Surface Salinities [Level 2C, Level 3 Running 8-day, Level 3 Monthly], Version 2.0 validated release. Remote Sensing Systems, Santa Rosa, CA, USA. Available online at,  doi: 10.5067/SMP20-xxxxx.

In the doi, the string xxxxx is:

  1. 2SOCS for the L2C files.
  2. 3SPCS for the L3 8-day running maps.
  3. 3SMCS for the L3 monthly maps.

Continued production of this data set requires support from NASA.  We need you to be sure to cite these data when used in your publications so that we can demonstrate the value of this data set to the scientific community.  Please include the following statement in the acknowledgement section of your paper:

"SMAP salinity data are produced by Remote Sensing Systems and sponsored by the NASA Ocean Salinity Science Team.  They are available at"