Assessment of the SMAP Level-4 Surface and Root-Zone Soil Moisture Product Using In Situ Measurements Academic Article uri icon

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abstract

  • 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.

authors

  • Reichle, Rolf H
  • De Lannoy, Gabrielle JM
  • Liu, Qiang
  • Ardizzone, Joseph V
  • Colliander, Andreas
  • Conaty, Austin
  • Crow, Wade
  • Jackson, Thomas J
  • Jones, Lucas A
  • Kimball, John S
  • Koster, Randal D
  • Mahanama, Sarith P
  • Smith, Edmond B
  • Berg, Aaron
  • Bircher, Simone
  • Bosch, David
  • Caldwell, Todd G
  • Cosh, Michael
  • González-Zamora, Ángel
  • Holifield Collins, Chandra D
  • Jensen, Karsten H
  • Livingston, Stan
  • Lopez-Baeza, Ernesto
  • Martínez-Fernández, José
  • McNairn, Heather
  • Moghaddam, Mahta
  • Pacheco, Anna
  • Pellarin, Thierry
  • Prueger, John
  • Rowlandson, Tracy
  • Seyfried, Mark
  • Starks, Patrick
  • Su, Zhongbo
  • Thibeault, Marc
  • van der Velde, Rogier
  • Walker, Jeffrey
  • Wu, Xiaoling
  • Zeng, Yijian

publication date

  • October 1, 2017