Soil Moisture Active Passive (SMAP)

Mission Specification & Status

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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 2 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.

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

SMAP Sea Surface Salinity

RSS SMAP Sea Surface Salinity 70km 8-Day Global Animation

Animation of global sea surface salinity (SSS) over the period 27-03-2015 to 16-04-2018 based on the 8-day running mean version 2.0 SMAP product from Remote Sensing Systems (RSS) at a spatial resolution of 70km.
The data set can be downloaded from PODAAC Portal at https://podaac.jpl.nasa.gov/dataset/SMAP_RSS_L3_SSS_SMI_8DAY-RUNNINGMEAN_V2_70KM

 

RSS SMAP Sea Surface Salinity 70km 8-Day Animation

Animation of sea surface salinity (SSS) over the period 27-03-2015 to 16-04-2018 based on the 8-day running mean version 2.0 SMAP product from Remote Sensing Systems (RSS) at a spatial resolution of 70km.
The data set can be downloaded from PODAAC Portal at https://podaac.jpl.nasa.gov/dataset/SMAP_RSS_L3_SSS_SMI_8DAY-RUNNINGMEAN...

News and Announcements (chronological order)

JPL SMAP Sea Surface Salinity (SSS) CAP V4.0 Dataset released

Thursday, February 22, 2018

The PO.DAAC is pleased to announce the availability of the PI-produced JPL V4.0 SMAP Sea Surface Salinity (SSS) and extreme winds data.  This release includes Level-2B and Level 3 products based on the JPL Combined Active-Passive (CAP) algorithm applied to data from the NASA Soil Moisture Active Passive (SMAP) observatory. Data begins April 1, 2015 and is ongoing. Improvements with this version include: addition of estimated SSS uncertainty fields, improvement of TB correction for high latitudes, modification of the land correction range to 1000 km from coast, change of the ancillary wind source from NCEP GDAS to NCEP GFS resulting in significant improvements in SSS retrievals near storms, extension of the range of SSS retrievals to 45 PSU, and SSS retrievals also for large inland seas.

Data sets comprising this release include the Level 2B (L2B) orbital data and two Level 3 (L3) 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 the L2B is provided on a 25 km swath grid while the L3s are gridded at 0.25o x 0.25o. The spatial resolution of all three products is approximately at 60 km.  The L2B product is in HDF5 format, and the L3 products are in netCDF4 file format.  All products are CF/ACDD metadata standards compliant.

The JPL SMAP-SSS CAP V4.0 data sets are described and discoverable via the PO.DAAC data portal.   Access to these data is via PO.DAAC’s public FTP site ftp://podaac.jpl.nasa.gov/allData/smap/.  The data can also be accessed via OPeNDAP, and PODAAC-WS, and are also be accessible via THREDDS and LAS.

The SMAP Algorithm Theoretical 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: podaac@podaac.jpl.nasa.gov


SMAP Sea Surface Salinity (SSS) V2.0 70km Dataset from Remote Sensing Systems (RSS) released

Wednesday, April 25, 2018

The PO.DAAC is pleased to announce the availability of updated version 2.0 SMAP Sea Surface Salinity (SSS) data from Remote Sensing Systems (RSS) at a spatial resolution of 70km.  

As is the case for the 40-km resolution product, the 70-km product is resampled onto a 0.25° fixed Earth grid using a Backus-Gilbert type optimum interpolation (OI). In the case of the 70-km product, the target cell of the OI is a circular footprint with a diameter of 70 km. Compared to the 40-km product, the 70-km is spatially smoother and the random noise is reduced by 60%. For most oceanographic applications, it is recommended that the new 70-km product be used.

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.  All products are in the netCDF4 file format, and the L3 products are CF/ACDD metadata standards compliant.  The formats of the 40km and 70 km products are the same.

The SMAP-SSS V2.0 70km data sets are described and discoverable via the PO.DAAC data portal.  Access to these data is via PO.DAAC’s public FTP site ftp://podaac.jpl.nasa.gov/allData/smap/.  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: podaac@podaac.jpl.nasa.gov


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