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AQUARIUS/SAC-D Soil Moisture Product Using V3.0 Observations
[13-Nov-14] Bindlish, R., Jackson, T., and Cosh, M.
Presented at the 2014 Aquarius/SAC-D Science Team Meeting
Although Aquarius was designed for ocean salinity mapping, our objective in this investigation is to exploit the large amount of land observations that Aquarius acquires and extend the mission scope to include the retrieval of surface soil moisture. The soil moisture retrieval algorithm development has focused on using only the radiometer data because of the extensive heritage of passive microwave retrieval of soil moisture. The Single Channel Algorithm (SCA) was implemented using the Aquarius observations to estimate surface soil moisture. SCA is also the baseline algorithm for the Soil Moisture Active Passive (SMAP) radiometer-only soil moisture product. Ancillary data inputs required for using the SCA are vegetation water content, land surface temperature, and several soil and vegetation parameters based on land cover classes. The Aquarius soil moisture algorithm that was initially implemented with Aquarius V2.0 dataset was modified to account for the adjustments made in v3.0 dataset. Aquarius v3.0 brightness temperature observations are lower than v2.0 observations by about 4-5K over land. The recalibration module to correct for the higher brightness temperatures in Aquarius 2.0 observations was removed from v3.0 soil moisture code.
The resulting global spatial patterns of soil moisture are consistent with the precipitation climatology and with soil moisture from other satellite missions (Advanced Microwave Scanning Radiometer-E and the Soil Moisture Ocean Salinity (SMOS)). Assessments were performed using in situ observations from the USDA Little Washita and Little River watershed soil moisture networks. Results showed good performance by the algorithm for these land surface conditions for the period of August 2011-June 2014 (RMSE=0.041 m3/m3, aRMSE=0.034 m3/m3, Bias=-0.013 m3/m3, and R=0.838). We are currently expanding our in situ observations to extend the validation of the Aquarius soil moisture product to other geographical domains. This radiometer-only soil moisture product will serve as a baseline for continuing research on both active and combined passive-active soil moisture algorithms. The products are routinely available through the NASA data archive at the National Snow and Ice Data Center (NSIDC).

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