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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, added x and y coordinate variables as well as an EASE-Grid 2.0 projection grid mapping variable, and 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 Geophysical Data, Version 4 [Dataset]. NASA National Snow and Ice Data Center Distributed Active Archive Center. https://doi.org/10.5067/KPJNN2GI1DQR Date Accessed: 2026-07-28
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 Geophysical Data, Version 4 [Dataset]. NASA National Snow and Ice Data Center Distributed Active Archive Center. https://doi.org/10.5067/KPJNN2GI1DQR Date Accessed: 2026-07-28
Reichle, Rolf, et al. “SMAP L4 Global 3-Hourly 9 Km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data, Version 4.” NASA National Snow and Ice Data Center Distributed Active Archive Center, 2018, https://doi.org/10.5067/KPJNN2GI1DQR. Date Accessed: 2026-07-28
Beck, Hylke E., Pan, Ming, Miralles, Diego G., Reichle, Rolf H., Dorigo, Wouter A., Hahn, Sebastian, Sheffield, Justin, Karthikeyan, Lanka, Balsamo, Gianpaolo, Parinussa, Robert M., van Dijk, Albert I. J. M., Du, Jinyang, Kimball, John S., Vergopolan, Noemi, Wood, Eric F.