Document Type
Article
Publication Title
Journal of Hydrometeorology
Publication Date
10-2017
Volume
18
First Page
2621
Last Page
2645
Abstract
The Soil Moisture Active Passive (SMAP) mission Level-4 Surface and Root-Zone Soil Moisture (L4_SM) data product is generated by assimilating SMAP L-band brightness temperature observations into the NASA Catchment land surface model. The L4_SM product is available from 31 March 2015 to present (within 3 days from real time) and provides 3-hourly, global, 9-km resolution estimates of surface (0–5 cm) and root-zone (0–100 cm) soil moisture and land surface conditions. This study presents an overview of the L4_SM algorithm, validation approach, and product assessment versus in situ measurements. Core validation sites provide spatially averaged surface (root zone) soil moisture measurements for 43 (17) “reference pixels” at 9- and 36-km gridcell scales located in 17 (7) distinct watersheds. Sparse networks provide point-scale measurements of surface (root zone) soil moisture at 406 (311) locations. Core validation site results indicate that the L4_SM product meets its soil moisture accuracy requirement, specified as an unbiased RMSE (ubRMSE, or standard deviation of the error) of 0.04 m3 m−3 or better. The ubRMSE for L4_SM surface (root zone) soil moisture is 0.038 m3 m−3 (0.030 m3 m−3) at the 9-km scale and 0.035 m3 m−3 (0.026 m3 m−3) at the 36-km scale. The L4_SM estimates improve (significantly at the 5% level for surface soil moisture) over model-only estimates, which do not benefit from the assimilation of SMAP brightness temperature observations and have a 9-km surface (root zone) ubRMSE of 0.042 m3 m−3 (0.032 m3 m−3). Time series correlations exhibit similar relative performance. The sparse network results corroborate these findings over a greater variety of climate and land cover conditions.
Keywords
Soil moisture; Soil temperature; Satellite observations; Kalman filters; Data assimilation; Land surface model
DOI
https://doi.org/10.1175/JHM-D-17-0063.1
Rights
© 2017 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).
Recommended Citation
Reichle, R.H., G.J. De Lannoy, Q. Liu, J.V. Ardizzone, A. Colliander, A. Conaty, W. Crow, T.J. Jackson, L.A. Jones, J.S. Kimball, R.D. Koster, S.P. Mahanama, E.B. Smith, A. Berg, S. Bircher, D. Bosch, T.G. Caldwell, M. CoshÁngel González-Zamora, C.D. Holifield Collins, K.H. Jensen, S. Livingston, E. Lopez-Baeza, J. Martínez-Fernández, H. McNairn, M. Moghaddam, A. Pacheco, T. Pellarin, J. Prueger, T. Rowlandson, M. Seyfried, P. Starks, Z. Su, M. Thibeault, R. van der Velde, J. Walker, X. Wu, and Y. Zeng, 2017: Assessment of the SMAP Level-4 Surface and Root-Zone Soil Moisture Product Using In Situ Measurements. J. Hydrometeor., 18, 2621–2645, https://doi.org/10.1175/JHM-D-17-0063.1