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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

Product Summary

Platforms
GEOS-5 ,
SMAP
Instruments
NOT APPLICABLE ,
SMAP L-BAND RADIOMETER
Spatial Extent

N: 85.044 S: -85.044 E: 180 W: -180

Spatial Resolution
9 Kilometers x 9 Kilometers
Spatial Reference System(s)
WGS 84 / NSIDC EASE-Grid 2.0 Global (EPSG:6933)
Location
GLOBAL LAND
Coordinate System
CARTESIAN
Granule Spatial Representation
CARTESIAN
Temporal Extent
2015-03-31 to Present
Temporal Resolution
3 Hour
Concept ID
C3480440870-NSIDC_CPRD
Data State
ACTIVE
Number of Files/Granules
33296
Processing Level
4
Published
Science Keywords
Root Zone Soil Moisture ,
Surface Soil Moisture

Citation

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

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

Documents

Publications Citing This Dataset

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Title Year Author Topic
Comparing Satellite Soil Moisture Products Using In Situ Observations over an Instrumented Experimental Basin in Romania Ortenzi, Sofia, Cencetti, Corrado, Mincu, Florentina-Iuliana, Neculau, Gianina, Chendes, Viorel, Ciabatta, Luca, Massari, Christian, Di Matteo, Lucio Root Zone Soil Moisture, Surface Soil Moisture
A near-linear transect sampling method for validation of SMAP surface soil moisture in non-complex terrains Cheruiyot, Elijah, Mito, Collins, Menenti, Massimo Root Zone Soil Moisture, Surface Soil Moisture
A Soil Moisture and Vegetation-Based Susceptibility Mapping Approach to Wildfire Events in Greece Chaleplis, Kyriakos, Walters, Avery, Fang, Bin, Lakshmi, Venkataraman, Gemitzi, Alexandra Root Zone Soil Moisture, Surface Soil Moisture
Evaluation of global seamless soil moisture products over China: A perspective of soil moisture sensitivity to precipitation Hong, Xu, Jia, Shaofeng, Zhu, Wenbin, Song, Zikun Surface Pressure, Heat Flux, Longwave Radiation, Shortwave Radiation, Surface Temperature, Humidity, Evapotranspiration, Surface Winds, Rain, Precipitation Rate, Snow, Soil Moisture/Water Content, Soil Temperature, Land Surface Temperature, Snow Water Equivalent, Runoff, Root Zone Soil Moisture, Surface Soil Moisture
A Spatial Downscaling Framework for SMAP Soil Moisture Based on Stacking Xu, Jiaxin, Su, Qiaomei, Li, Xiaotao, Ma, Jianwei, Song, Wenlong, Zhang, Lei, Su, Xiaoye Surface Soil Moisture, Root Zone Soil Moisture
Soil Moisture, Soil NOx and Regional Air Quality in the Agricultural Central United States Huber, Daniel E., Kort, Eric A., Steiner, Allison L. Root Zone Soil Moisture, Surface Soil Moisture
A Performance Analysis of Soil Dielectric Models over Organic Soils in Zhang, Runze, Chan, Steven, Bindlish, Rajat, Lakshmi, Venkataraman Brightness Temperature, Surface Soil Moisture, Root Zone Soil Moisture
Assessing Regional Ecosystem Conditions Using Geospatial Techniques-A Zhang, Chunhua, Wang, Kelin, Yue, Yuemin, Qi, Xiangkun, Zhang, Mingyang Root Zone Soil Moisture, Surface Soil Moisture
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