Assessing SMAP soil moisture scaling and retrieval in the Carman (Canada) study site

Authors: BHUIYAN, H. - Agriculture And Agri-Food Canada; MCNAIRN, H. - Agriculture And Agri-Food Canada; POWERS, J. - Agriculture And Agri-Food Canada; FRIESEN, M. - Agriculture And Agri-Food Canada; PACHECO, A. - Agriculture And Agri-Food Canada; Jackson, Thomas; Cosh, Michael; COLLIANDER, A. - Jet Propulsion Laboratory; BERG, A. - University Of Guelph; ROWLANDSON, T. - University Of Guelph; MAGAGI, R. - Universite De Sherbrooke

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2018
Publication Date: 12/20/2018
Citation: Bhuiyan, H., McNairn, H., Powers, J., Friesen, M., Pacheco, A., Jackson, T.J., Cosh, M.H., Colliander, A., Berg, A., Rowlandson, T., Magagi, R. 2018. Assessing SMAP soil moisture scaling and retrieval in the Carman (Canada) study site. Vadose Zone Journal. 17(1). https://doi.org/10.2136/vzj2018.07.0132.
DOI: https://doi.org/10.2136/vzj2018.07.0132

Interpretive Summary: The NASA Soil Moisture Active Passive (SMAP) Validation Experiment in 2016 took place in the summer of 2016 near Winnipeg, Canada. Its purpose was to investigate errors which have been observed between the soil moisture from SMAP and the in situ network located in the agricultural domain around the town of Carman, Manitoba. The network was calibrated and compared using multiple scaling methodologies to determine the best approach of bridging the spatial gap between the network and the remote sensing scale. All methods yielded similar high errors, indicating that none of the studied variables in the experiment are able to reduce the validation errors of the network to an acceptable level. Further work will need to be done to determine how the satellite algorithm can be improved.

Technical Abstract: In 2015 NASA launched the Soil Moisture Active Passive (SMAP) satellite. Data from this satellite are being exploited to improve forecasting of extreme weather events and delivery of disaster response. International core validation sites (CVS) have been contributing in-situ soil moisture data to validation and calibrate SMAP soil moisture products. Overall the soil moisture retrieval errors have exceeded SMAP’s mission requirement (errors below 0.04 m3/m3), with the exception of some sites of annual cropland as present at the Carman (Canada) CVS. In 2016, a SMAP Validation Experiment was conduced at the Canadian site in Manitoba (SMAPVEX16-MB) in an attempt to understand the differences between the SMAP soil moisture retrievals and the permanent in-situ network observations. The research presented in this paper analyzed the performance of this network in representing soil moisture within a SMAP pixel and tested five upscaling approaches. Comparisons between the permanent network and SMAPVEX16-MB measurements (from temporary stations and field measures) confirmed agreement among these three sources of soil moisture measures. SMAP soil moisture values were compared to in-situ soil moisture upscaled from the four tested approaches, as well as soil moisture estimated by the NOAH Land Surface Model (LSM). There were similar discrepancies when analyzing all methods (root mean square errors from 0.072 – 0.074 m3/m3 for the four upscaling methods; 0.076 m3/m3 for the LSM approach), yielding no reduction in the soil moisture root mean square error for this site. The SMAP team will continue to investigate other factors that may be contributing to errors above 0.04 m3/m3 at these annually cropped CVS sites.