Spatial patterns of SMOS downscaled soil moisture maps over the remedhus network (Spain)

Abstract

This paper describes the relationships found between remotely sensed soil moisture, in situ observed soil moisture, and spatial distribution of soil and climatic factors. For the comparison between remote and in situ soil moisture, soil moisture map series at high resolution, obtained by applying a downscaling approach that combines Soil Moisture and Ocean Salinity (SMOS) and MODIS imagery is extracted. The in situ soil moisture series are obtained from the Soil Moisture Measurement Stations Network (REMEDHUS) in Spain. For the spatial analysis, factors such as topography, precipitation, and land uses were mapped from the climatic and cartographic database of REMEDHUS. The comparison between downscaled and in situ soil moisture data resulted in correlation coefficient (R) values between 0.40 and 0.70, bias between -0.04 and 0.16 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 root mean squared difference (RMSD) between 0.07 and 0.19 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> . Regarding the spatial correlations between downscaled and spatial factors, no clear patterns were found when considering the topography (Topographic Wetness Index, TWI), and the land uses (Landsat classification). Nevertheless, the downscaled soil moisture was more related with the spatial distribution of precipitation (Antecedent Precipitation Index, API), with significant correlations varying between 0.24 and 0.55.