Triple Collocation Analysis and In Situ Validation of the CYGNSS Soil Moisture Product

Abstract

Cyclone Global Navigation Satellite System (CYGNSS) soil moisture (SM) product is characterized by high temporal resolution, but the relative strengths and weaknesses of this new product are unknown. In this study, we analyze the performance of CYGNSS SM product across varied land covers and climates, using the triple collocation (TC) analysis and in-situ validation. The Soil Moisture Active Passive (SMAP), Advanced Microwave Scanning Radiometer 2 (AMSR2) Land Parameter Retrieval Model (LPRM), and European Space Agency Climate Change Initiative (ESA CCI) Active SM products were used as references as well as data alternatives to calculate TC-based standard deviation ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SD_TC</i> ), correlation ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R_TC</i> ), and in-situ validation Pearson's correlation coefficient (R), unbiased root-mean-square error (ubRMSE). The TC analysis indicated that CYGNSS had a relatively low median <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SD_TC</i> of 0.024 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> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R_TC</i> of 0.419. Validation based on 251 in-situ SM stations showed that CYGNSS obtained a relatively low median ubRMSE of 0.057 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>

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