Abstract
In August 2020, soil moisture active passive (SMAP) released a new version of its soil moisture and vegetation optical depth (VOD) retrieval products. In this article, we review the methodology followed by the SMAP regularized dual-channel retrieval algorithm. We show that the new implementation generates SM retrievals that not only satisfy the SMAP accuracy requirements, but also show a performance comparable to the single-channel algorithm that uses the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> polarized brightness temperature. Due to a lack of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> measurements we cannot evaluate the accuracy of the VOD. In this article, we show analyses with the intention of providing an understanding of the VOD product. We compare the VOD results with those from SMOS. We also study the relation of the SMAP VOD with two vegetation parameters: tree height and biomass.
Highlights
T HE soil moisture active passive (SMAP) mission was designed to acquire and combine L-band radar and radiometer measurements for the estimation of soil moisture (SM) with an average unbiased root-mean square error of no more than 0.04 m3/m3 volumetric accuracy in the top 5 cm of soil for vegetation with water content of less than 5 kg/m2 [1], [2]
We looked into the time difference between the Normalized Difference Vegetation Index (NDVI) τ ∗ peak location and the peak location of the RDCA vegetation optical depth (VOD) climatology and for MDCA VOD and RDCA VOD
core validation sites (CVSs) assessment of soil moisture retrievals. 5 years (04/01/2015-03/31/2020) of data were used to compare the accuracy of MDCA with SCA-V and RDCA
Summary
T HE soil moisture active passive (SMAP) mission was designed to acquire and combine L-band radar and radiometer measurements for the estimation of soil moisture (SM) with an average unbiased root-mean square error (ubRMSE) of no more than 0.04 m3/m3 volumetric accuracy in the top 5 cm of soil for vegetation with water content of less than 5 kg/m2 [1], [2]. The new implementation of the dual channel algorithm (DCA), which uses the two polarized brightness temperature measurements (H and V), generates SM retrievals, . In order to understand the performance of the VOD product, it is common to compare it to similar products from other missions and to look at it in relation to other vegetation parameters such as tree height and biomass. The soil moisture and ocean salinity (SMOS) mission [6], produces simultaneous retrievals of SM and VOD based on angular information in its V- and H-pol brightness temperature products. CHAUBELL et al.: REGULARIZED DUAL-CHANNEL ALGORITHM FOR THE RETRIEVAL OF SOIL MOISTURE AND VOD
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