Improved SMAP Dual-Channel Algorithm for the Retrieval of Soil Moisture
Julián Chaubell, Simon Yueh, R. S. Dunbar, Andreas Colliander, Fan Chen, S. Chan, Dara Entekhabi, Rajat Bindlish, Peggy O’Neill, Jun Asanuma, Aaron Berg, David D. Bosch, Todd G. Caldwell, Michael H. Cosh, Chandra Holifield Collins, José Martínez‐Fernández, M. S. Seyfried, Patrick J. Starks, Zhongbo Su, M. Thibeault, Jeffrey P. Walker
Abstract
The soil moisture active passive (SMAP) mission was designed to acquire L-band radiometer measurements for the estimation of soil moisture (SM) with an average ubRMSD of not more than 0.04 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> volumetric accuracy in the top 5 cm for vegetation with a water content of less than 5 kg/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Single-channel algorithm (SCA) and dual-channel algorithm (DCA) are implemented for the processing of SMAP radiometer data. The SCA using the vertically polarized brightness temperature (SCA-V) has been providing satisfactory SM retrievals. However, the DCA using prelaunch design and algorithm parameters for vertical and horizontal polarization data has a marginal performance. In this article, we show that with the updates of the roughness parameter h and the polarization mixing parameters Q, a modified DCA (MDCA) can achieve improved accuracy over DCA; it also allows for the retrieval of vegetation optical depth (VOD or τ). The retrieval performance of MDCA is assessed and compared with SCA-V and DCA using four years (April 1, 2015 to March 31, 2019) of in situ data from core validation sites (CVSs) and sparse networks. The assessment shows that SCA-V still outperforms all the implemented algorithms.