Soil Moisture: Analysis of SMAP Satellite Products in Plain Zones

Soil moisture (SM) plays a vital role in the water and energy cycles, affecting evapotranspiration, infiltration, and runoff processes. The SM available for evapotranspiration is crucial for food security, especially given the significant in-terannual variability in the yield of rainfed crops in large agricultural regions. Due to the limited availability of field data, satellite-derived values are essential for studying SM. Therefore, evaluating this information across different surfaces, climates, and soil types is paramount. This study analyzed SMAP data (36 km, 9 km, and rescaled to 1 km) and the SMAP/Sentinel-1 product (1 km and 3 km) concerning field data to understand the behavior of SM products with different spatial resolutions. The study areas include short grass and rainfed crop zones in the Pampean region of Argentina and in Northern Italy, ranging from semiarid to subhumid/humid climates. In both regions, results showed that the 9 km product exhibits errors between 5% and 15% in the Pampean region and 7% in Italy. While the 36 km data behaves similarly, higher spatial resolution data shows increased errors, ranging from 5% to around 20%. Therefore, it is recommended to consider validations for the 1 km and 3 km products and avoid using them directly without prior evaluation.