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Description
SMAP Level-4 (L4) surface and root zone soil moisture data are provided in three products:
SMAP L4 Global 3-hourly 9 km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data (SPL4SMGP, DOI: 10.5067/KPJNN2GI1DQR)
SMAP L4 Global 3-hourly 9 km EASE-Grid Surface and Root Zone Soil Moisture Analysis Update (SPL4SMAU, DOI: 10.5067/60HB8VIP2T8W)
SMAP L4 Global 9 km EASE-Grid Surface and Root Zone Soil Moisture Land Model Constants (SPL4SMLM, DOI: 10.5067/KGLC3UH4TMAQ).
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: Revisions to the land surface modeling system; Revisions to the parameters and parameterizations of the surface energy balance and the snow depletion curve; Analysis increments are no longer computed for the “catchment deficit” model prognostic variable in the Ensemble Kalman filter update step; Added x and y coordinate variables as well as an EASE-Grid 2.0 projection grid mapping variable; Minor bug fixes.
For the full major and minor version history, go to https://nsidc.org/data/smap/data_versions.
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. (2018). SMAP L4 Global 3-hourly 9 km EASE-Grid Surface and Root Zone Soil Moisture Analysis Update, Version 4 [Data set]. NASA National Snow and Ice Data Center Distributed Active Archive Center. https://doi.org/10.5067/60HB8VIP2T8W Date Accessed: 2026-06-11
Reichle, Rolf, Gabrielle De Lannoy, Randal Koster, Wade Crow, John Kimball, and Qing Liu. “SMAP L4 Global 3-Hourly 9 Km EASE-Grid Surface and Root Zone Soil Moisture Analysis Update, Version 4.” NASA National Snow and Ice Data Center Distributed Active Archive Center, 2018. doi:10.5067/60HB8VIP2T8W. Date Accessed: 2026-06-11
Reichle, Rolf, et al. SMAP L4 Global 3-Hourly 9 Km EASE-Grid Surface and Root Zone Soil Moisture Analysis Update, Version 4. NASA National Snow and Ice Data Center Distributed Active Archive Center, 2018, doi:10.5067/60HB8VIP2T8W. Date Accessed: 2026-06-11