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Description
This Level-2 (L2) soil moisture product provides estimates of land surface conditions retrieved by both the Soil Moisture Active Passive (SMAP) radiometer during 6:00 a.m. descending and 6:00 p.m. ascending half-orbit passes and the Sentinel-1A and -1B radar. SMAP L-band brightness temperatures and Copernicus Sentinel-1 C-band backscatter coefficients are used to derive soil moisture data, which are then resampled to an Earth-fixed, cylindrical 3 km Equal-Area Scalable Earth Grid, Version 2.0 (EASE-Grid 2.0). While the 3 km data product has undergone validation, the 1 km product has not and should be used with caution.
Version Description
Changes to this version include:
- An improved calibration methodology was applied to the SMAP Level-1B brightness temperatures.
- Revised the coefficients in the land surface temperature computation to be consistent with the SMAP Level-2 soil moisture passive enhanced product. The new coefficients are C=0.246, K=1.007 for AM passes and C=1.0, K=1.007 for PM passes.
- Changed the omega parameter of the tau-omega model for forest landcover classes (1-5) from 0.05 to 0.07.
- Uses a new high-resolution soil database (SoilGrid250m; Hengl et al., 2017).
- Uses bulk density to set the upper limit of the soil moisture retrievals. Previous versions used a fixed value of 0.65 m3/m3.
- Enhanced documentation on Data Flags in the User Guide to help data users to better understand and use the flags.
- Added a bit in the TB Disaggregation QC flag to indicate (1) the use of SMAP AM or PM data; and (2) the time difference (greater or less than 36 hours) between the SMAP and Sentinel observations overlap.
- Fixed the EASE_[row/column]_index_apm_[1km/3km] data fields to make them 0-based.
- Fixed the range beginning and ending time in the file metadata.
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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Das, N., Entekhabi, D., Dunbar, R., Kim, S., Yueh, S., Colliander, A., ONeill, P., Jackson, T., Jagdhuber, T., Chen, F., Crow, W., Walker, J., Berg, A., Bosch, D., Caldwell, T., & Cosh, M. (2020). SMAP/Sentinel-1 L2 Radiometer/Radar 30-Second Scene 3 km EASE-Grid Soil Moisture, Version 3 [Data set]. NASA National Snow and Ice Data Center Distributed Active Archive Center. https://doi.org/10.5067/ASB0EQO2LYJV Date Accessed: 2026-05-03
Das, Narendra, Dara Entekhabi, Roy Dunbar, Seungbum Kim, Simon Yueh, Andreas Colliander, Peggy ONeill, et al. “SMAP/Sentinel-1 L2 Radiometer/Radar 30-Second Scene 3 Km EASE-Grid Soil Moisture, Version 3.” NASA National Snow and Ice Data Center Distributed Active Archive Center, 2020. doi:10.5067/ASB0EQO2LYJV. Date Accessed: 2026-05-03
Das, Narendra, et al. SMAP/Sentinel-1 L2 Radiometer/Radar 30-Second Scene 3 Km EASE-Grid Soil Moisture, Version 3. NASA National Snow and Ice Data Center Distributed Active Archive Center, 2020, doi:10.5067/ASB0EQO2LYJV. Date Accessed: 2026-05-03