Validation of soil moisture data products from the NASA SMAP mission

Authors: COLLIANDER, A. - Jet Propulsion Laboratory; REICHLE, R. - National Aeronautics And Space Administration (NASA); Crow, Wade; Cosh, Michael; CHEN, F. - Science Systems And Applications, Inc; CHAN, S. - Jet Propulsion Laboratory; DAS, N. - Jet Propulsion Laboratory; BINDLISH, R. - National Aeronautics And Space Administration (NASA); CHAUBELL, J. - Jet Propulsion Laboratory; LIU, Q. - National Aeronautics And Space Administration (NASA); O'NEILL, P. - National Aeronautics And Space Administration (NASA) - Johnson Space Center; DUNBAR, R. - Jet Propulsion Laboratory; DANG, L. - Jet Propulsion Laboratory; KIMBALL, J. - University Of Montana; AL JASSAR, H. - Kuwait University; ASANUMA, J. - University Of Tsukuba; BHATTACHARYA, K. - Collaborator; BERG, A. - University Of Guelph; Bosch, David; BOURGEAU-CHAVEZ, L. - Michigan Technological University; CALDWELL, T. - Us Geological Survey (USGS); CALVERT, J. - Collaborator; DORIGO, W. - Vienna University Of Technology; Holifield Collins, Chandra; JENSEN, K. - University Of Copenhagen; Livingston, Stanley; LOPEZ-BAEZA, E. - Valencia University; MARTINEZ-FERNANDEZ, J. - Collaborator; MCNAIRN, H. - Agriculture And Agri-Food Canada; MOGHADDAM, M. - University Of Southern California; MONTZKA, C. - Juelich Research Center; NOTARNICOLA, C. - Collaborator; PELLARIN, T. - Universite Grenoble Alpes; Prueger, John; PULLIAINEN, J. - Finnish Meteorological Institute; RAMOS, J. - Universidad Nacianal Autonoma De Mexico; Seyfried, Mark; Starks, Patrick; SU, Z. - University Of Twente; THIBEAULT, M. - Collaborator; WALKER, J. - Monash University; ENTEKHABI, D. - Collaborator; YUEH, S. - Jet Propulsion Laboratory

Submitted to: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2021
Publication Date: 11/13/2021
Citation: Colliander, A. Reichle, R.H., Crow, W.T., Cosh, M.H., Chen, F., Chan, S., Das, N., Bindlish, R., Chaubell, M.J., Kim, S.B., Liu, Q., O’Neill, P., Dunbar, R.S., Dang, L., Kimball, J., Jackson, T.J., al Jassar, J.K., Asanuma, J., Bhattacharya, B.K., Berg, A., Bosch, D.D., Bourgeau-Chavez, L., Caldwell, T., Calvet, J-C., Dorigo, W., Holifield Collins, C., Jensen, K., Livingston, S., Lopez-Baeza, E., Martínez-Fernández, J., McNairn, H., Moghaddam, M., Montzka, C., Notarnicola, C., Pellarin, T., Prueger, J., Pulliainen, J., Ramos, J., Seyfried, M., Starks, P., Su, Z., van der Velde, R., Zeng, Y., Thibeault, M., Walker, J.P., Zribi, M., Entekhabi, D., and Yueh, S. 2022. Validation of Soil Moisture Data Products from the NASA SMAP Mission. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. 15:364-392. https://doi.org/10.1109/JSTARS.2021.3124743.
DOI: https://doi.org/10.1109/JSTARS.2021.3124743

Interpretive Summary: Launched in 2015, the NASA Soil Moisture Active/Passive (SMAP) mission represents the culmination of over three decades of effort by USDA scientists to develop a viable approach for measuring soil moisture from space. Now that six years of SMAP data have been acquired, it is critical to assess the performance of the soil moisture estimates it generates and ensure that they are meeting accuracy requirements defined by key agricultural applications. This paper provides the most in-depth, and longest, such assessment of SMAP soil moisture products to date. By examining a range of validation sources - including intensive ground soil moisture networks operated by the USDA Agricultural Research Service - this paper demonstrates that SMAP soil moisture data products are generally meeting their pre launch accuracy goals. These results will further the operational use of SMAP data products for agricultural monitoring and management applications.

Technical Abstract: NASA’s Soil Moisture Active Passive (SMAP) mission has been conducting comprehensive validation of its soil moisture (SM) products since the start of data production on March 31, 2015. Prior to launch, the mission defined a set of criteria for core validation sites (CVS) that enable the testing of the key mission SM accuracy requirement (i.e., an average unbiased root-mean-square error across the CVS of less than 0.04 m^3/m^3). The validation approach also includes other (“sparse network”) in situ SM measurements, other global spaceborne SM products, global model-based SM products, and field experiments. Over the past six years, the SMAP SM products have been analyzed with respect to the reference data, and the analysis approaches themselves have been exposed to scrutiny in an effort to best understand the products’ performance. Validation of the most recent SMAP Level 2 and 3 SM retrieval products (R17000) shows that the radiometer-based SM continues to meet mission requirements. The radiometer-based retrieval product is generally consistent with SM retrievals from the ESA Soil Moisture Ocean Salinity mission, although there are differences in some regions. The high-resolution (3-km) retrieval product, generated by combining Copernicus Sentinel-1 data with SMAP radiometer observations, performs within expectations. Currently, however, there is limited availability of high-resolution (3-km) CVS reference data to enable extensive validation at this spatial scale. The most recent (version 5) SMAP Level 4 SM data assimilation product provides surface and root-zone SM with complete spatio-temporal coverage at 9-km resolution and also meets performance requirements. The SMAP SM validation program will continue as long as the mission is active; future plans include expanding it to forested and high-latitude regions.