We are in the process of migrating all NASA Earth science data sites into Earthdata from now until end of 2026. Not all NASA Earth science data and resources will appear here until then. Thank you for your patience as we make this transition.Read about the Web Unification Project
Description
SMAP Level-4 (L4) surface and root zone soil moisture data are provided in three products: (1) SMAP L4 9 km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data (SPL4SMGP). (2) SMAP L4 9 km EASE-Grid Surface and Root Zone Soil Moisture Analysis Update (SPL4SMAU). (3) SMAP L4 9 km EASE-Grid Surface and Root Zone Soil Moisture Land Model Constants (SPL4SMLM).
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: (1) SMAP observations are now assimilated in Eastern Europe, the Middle East, and East Asia due to expanded coverage of the brightness temperature scaling parameters. The latter are based on two years of SMAP Version 3 brightness temperature observations where the SMOS climatology is unavailable due to RFI. (2) An improved version of the model-only Nature Run (NRv4.1) simulation is used to derive the brightness temperature scaling parameters, the model soil moisture initial conditions, and the soil moisture climatology. (3) Minor bug fixes.
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.
Copy Citation
Citation Copied
Reichle, R., De Lannoy, G., Koster, R., Crow, W., & Kimball, J. (2017). SMAP L4 9 km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data, Version 3 [Data set]. NASA National Snow and Ice Data Center Distributed Active Archive Center. https://doi.org/10.5067/B59DT1D5UMB4 Date Accessed: 2026-06-17
Reichle, Rolf, Gabrielle De Lannoy, Randal Koster, Wade Crow, and John Kimball. “SMAP L4 9 Km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data, Version 3.” NASA National Snow and Ice Data Center Distributed Active Archive Center, 2017. doi:10.5067/B59DT1D5UMB4. Date Accessed: 2026-06-17
Reichle, Rolf, et al. SMAP L4 9 Km EASE-Grid Surface and Root Zone Soil Moisture Geophysical Data, Version 3. NASA National Snow and Ice Data Center Distributed Active Archive Center, 2017, doi:10.5067/B59DT1D5UMB4. Date Accessed: 2026-06-17
Doughty, Christopher E., Keany, Jenna M., Wiebe, Benjamin C., Rey-Sanchez, Camilo, Carter, Kelsey R., Middleby, Kali B., Cheesman, Alexander W., Goulden, Michael L., da Rocha, Humberto R., Miller, Scott D., Malhi, Yadvinder, Fauset, Sophie, Gloor, Emanuel, Slot, Martijn, Oliveras Menor, Imma, Crous, Kristine Y., Goldsmith, Gregory R., Fisher, Joshua B.