Soil Moisture Active Passive (SMAP)

Mission Specification & Status


Launched on January 31, 2015, the NASA Soil Moisture Active Passive (SMAP) mission is designed to principally measure soil moisture and freeze/thaw state from space for all non-liquid water surfaces globally within the top layer of the Earth. The mission additionally provides a value-added Level 4 terrestrial carbon dataset derived from SMAP observations. 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. In approximately 3 days, SMAP achieves global coverage but has an exact orbit repeat cycle of 8 days.  Additional information on SMAP orbital characteristics and instruments, comprised of an L-band radar sensor and highly sensitive radiometer operating at 1.41GHz, is provided adjacent. Further details on the SMAP mission are available from the NASA SMAP website and SMAP Handbook.

SMAP is now also building upon the legacy of Aquarius/SAC-D mission in delivering both soil moisture and derived sea surface salinity (SSS) observations for the world’s oceans. With the loss of the Aquarius mission on June 7, 2015 it became critical also to continue the time series of global salinity observations important to studies of the earth’s water cycle.  Because both Aquarius and SMAP shared a L-band feed-horn configuration, lessons learned from the algorithm development under the Aquarius mission could be applied to SMAP to retrieve SSS via SMAP. However, because of the larger swath coverage, spatial resolutions under SMAP are approximately 40km instead of 100km with Aquarius. The increased spatial coverage provides opportunities for applying SMAP data for higher resolution studies than Aquarius. With the initiation of SMAP science operations and data flows in April of 2015, the approximate 3-month overlap period between SMAP and Aquarius also allows for inter-calibration and comparative studies.

The primary SMAP salinity products include a Level 2C orbital dataset, in which data granules contain both the ascending and descending arcs of the orbit, and two Level 3 gridded datasets: an 8-day running average product (linked to the day repeat cycle of SMAP) and a monthly product. SMAP salinity data are archived and distributed via the PODAAC. SMAP soil moisture and L4-Carbon products are available from the National Snow and Ice Data Center (NSIDC), with Level 1 SMAP radar data being distributed by the Alaska Satellite Facility (ASF).   These DAACs are the official NASA repositories for the SMAP mission data.

Figure 1: (Left) Global soil moisture mapped image from SMAP.   (Right)  Derived sea surface salinity (SSS) from SMAP  (8-day running mean composite)

News and Announcements

SMAP Sea Surface Salinity (SSS) V2.0 Dataset from Remote Sensing Systems (RSS) released

18 November, 2016

The PO.DAAC is pleased to announce the availability of the version 2.0 SMAP Sea Surface Salinity (SSS) data from Remote Sensing Systems (RSS).  This builds upon the legacy of the Aquarius/SAC mission and the official NASA salinity retrieval algorithm applied now to observations from the Soil Moisture Active Passive (SMAP) mission. Data begins April 1,2015 and is ongoing, with a one month latency in processing and data availability.

Data sets comprising this release include the Level 2C orbital data and two Level 3 mapped salinity products: an 8-day running mean product based on the repeat orbit of the SMAP mission, along with a monthly average product.  Both are global in extent and gridded at 25km x 25km resolution. All products are in the netCDF4 file format, and the L3 products are CF/ACDD metadata standards compliant.  

The SMAP-SSS V2.0 data sets are described and discoverable via the PO.DAAC data portal.   Access to these data is via PO.DAAC’s public FTP site  The data are also accessible via a range of PO.DAAC tools and services: OPeNDAPTHREDDSPODAAC-WS and LAS.

The SMAP Algorithm Theoreotical Basis Document (ATBD), validation analysis and file specification document together with other primary technical documentation, are available from the FTP site together with reader software.  General information regarding the SMAP mission is available from the mission website and also via PO.DAAC’s SMAP  and salinity webpages.

Should you have any questions, please contact us at:


See all Official NASA SMAP Mission News
See all PO.DAAC Announcements

SMAP Sea Surface Salinity

This video provides a global tour of sea surface salinity using measurements from NASA's SMAP over the period April to November 2015. Red represents areas of high salinity, while blue represents areas of low salinity. SMAP builds upon the Aquarius mission in measuring sea surface salinity from space and providing the global view of salinity variability needed for climate studies. The animation was produced and is provided courtesy of Remote Sensing Systems.