Validation of Soil Moisture Data Products from the NASA SMAP Mission
preprintposted on 04.06.2021, 21:35 by Andreas Colliander, Rolf Reichle, Wade Crow, Michael Cosh, Fan Chen, Steven Chan, Narendra Das, Rajat Bindlish, Julian Chaubell, Seungbum Kim, Qing Liu, Peggy O'Neill, Scott Dunbar, Lan Dang, John Kimball, Tom Jackson, Hala AlJassar, Jun Asanuma, Bimal Bhattacharya, Aaron Berg, David Bosch, Laura Bourgeau-Chavez, Todd Caldwell, Jean-Christophe Calvet, Chandra Holifield Collins, Karsten Jensen, Stan Livingston, Ernesto López-Baeza, José Martínez-Fernández, Heather McNairn, Mahta Moghaddam, Carsten Montzka, Claudia Notarnicola, Thierry Pellarin, Isabella Pfeil, Jouni Pulliainen, Judith Ramos, Mark Seyfrie, Patrick Starks, Z Su, Marc Thibeault, R. van der Velde, Mariette Vreugdenhil, Jeffrey Walker, Y. Zeng, Mehrez Zribi, Dara Entekhabi, Simon Yueh
NASA’s Soil Moisture Active Passive (SMAP) mission has been validating 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 (unbiased root-mean-square error <0.04 m3/m3). The validation approach also includes other (“sparse network”) in situ SM measurements, satellite SM products, model-based SM products, and field experiments. Over the past six years, the SMAP SM products have been analyzed with respect to these reference data, and the analysis approaches themselves have been scrutinized 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 L-band (1.4 GHz) radiometer-based SM record continues to meet mission requirements. The products are 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) SM retrieval product, generated by combining Copernicus Sentinel-1 data with SMAP observations, performs within expectations. Currently, however, there is limited availability of 3-km CVS data to support extensive validation at this spatial scale. The most recent (version 5) SMAP Level 4 SM data assimilation product providing surface and root-zone SM with complete spatio-temporal coverage at 9-km resolution also meets performance requirements. The SMAP SM validation program will continue throughout the mission life; future plans include expanding it to forested and high-latitude regions.