Delivery of Suomi National Polar-orbiting Partnership (Suomi NPP) satellite data products will cease on November 1, 2026. Data users should transition now to alternative products from NOAA-21 and NOAA-20.Suomi NPP data announcement
Description
SMAP Level-4 (L4) surface and root zone soil moisture (L4_SM) data are provided in three products.
The SMAP L4 Global 3-hourly 9 km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data (SPL4SMGP, DOI: 10.5067/T5RUATAQREF8) product is a series of 3-hourly time average geophysical land surface fields that are output by the L4_SM algorithm. It is likely of primary interest to most users.
The SMAP L4 Global 3-hourly 9 km EASE-Grid Surface and Root Zone Soil Moisture Analysis Update (SPL4SMAU, DOI: 10.5067/02LGW4DGJYRX) product provides diagnostics from the land surface analysis updates. It consists of a series of 3-hourly instantaneous (or snapshot) files that contain the assimilated SMAP observations, the corresponding land model predictions and analysis estimates, and additional data assimilation diagnostics.
Lastly, the SMAP L4 Global 9 km EASE-Grid Surface and Root Zone Soil Moisture Land Model Constants (SPL4SMLM, DOI: 10.5067/PXQIBL2ALDZD) product provides static (time-invariant) land surface model constants that will be needed by some users for further interpretation of the geophysical land surface fields. This product consists of only one granule (file) per L4_SM data product version (as defined by a distinct Science Version ID).
For each product, SMAP L-band brightness temperature data from descending and ascending half-orbit satellite passes (approximately 6:00 a.m. and 6:00 p.m. local solar time, respectively) are assimilated into a land surface model that is gridded using an Earth-fixed, global cylindrical 9 km Equal-Area Scalable Earth Grid, Version 2.0 (EASE-Grid 2.0) projection.
Version Description
Changes to this version include: The precipitation observations used outside of North America and the high latitudes are from Version 07 of the NASA Integrated Multi-satellitE Retrievals for the Global Precipitation Measurement mission (IMERG) products; The L-band microwave radiative transfer model (mwRTM) was updated; The Catchment land surface model now uses climatological snow albedo values based on observations from the NASA Moderate Resolution Imaging Spectroradiometer, replacing the look-up table parameterization of earlier L4_SM versions; The assimilated brightness temperatures are now taken only from Version 6 (“R19”) of the SPL1CTB product; The brightness temperature scaling parameters in the L4_SM algorithm are now based on nine years of SMAP observations and model simulations (April 2015 – March 2024); Bug fixes.
For the full major and minor version history, go to https://nsidc.org/data/smap/version-history
Citation is critically important for dataset documentation and discovery. This dataset is openly shared, without restriction, in accordance with the EOSDIS Data Use and Citation Guidance.
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Reichle, R., De Lannoy, G., Koster, R., Crow, W., Kimball, J., Liu, Q., & Bechtold, M. (2025). SMAP L4 Global 3-hourly 9 km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data, Version 8 [Dataset]. NASA National Snow and Ice Data Center Distributed Active Archive Center. https://doi.org/10.5067/T5RUATAQREF8 Date Accessed: 2026-08-24
@misc{reichle_de lannoy_koster_crow_kimball_liu_bechtold_2025,
title={SMAP L4 Global 3-hourly 9 km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data, Version 8},
url={https://nsidc.org/data/spl4smgp/versions/8},
DOI={10.5067/T5RUATAQREF8},
publisher={NASA National Snow and Ice Data Center Distributed Active Archive Center},
author={Reichle, Rolf and De Lannoy, Gabrielle and Koster, Randal and Crow, Wade and Kimball, John and Liu, Qing and Bechtold, Michel},
year={2025},
}
Reichle, R., De Lannoy, G., Koster, R., Crow, W., Kimball, J., Liu, Q., & Bechtold, M. (2025). SMAP L4 Global 3-hourly 9 km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data, Version 8 [Dataset]. NASA National Snow and Ice Data Center Distributed Active Archive Center. https://doi.org/10.5067/T5RUATAQREF8 Date Accessed: 2026-08-24
Reichle, Rolf, et al. “SMAP L4 Global 3-Hourly 9 Km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data, Version 8.” NASA National Snow and Ice Data Center Distributed Active Archive Center, 2025, https://doi.org/10.5067/T5RUATAQREF8. Date Accessed: 2026-08-24
Johnston, Miriam R., Barnes, Mallory L., Preisler, Yakir, Smith, William K., Biederman, Joel A., Scott, Russell L., Williams, A. Park, Dannenberg, Matthew P.
Cigarra-Guinez, Lorenzo E., Lagos, Octavio, Steduto, Pasquale, Krogh, Sebastian A., Shapiro, Kristen, Souto, Camilo, Lillo-Saavedra, Mario, Balbontin, Claudio, Zaccaria, Daniele