Evaluation of SMAP Soil Moisture Relative to Five Other Satellite Products Using the Climate Reference Network Measurements Over USA

Satellite platforms provide a unique opportunity to retrieve global soil moisture. The Level 3 soil moisture (L3SMP), enhanced Level 3 soil moisture (L3SMP-E) and Level 4 surface soil moisture (L4SM) products of the latest soil moisture satellite mission, Soil Moisture Active Passive (SMAP), are evaluated relative to five other satellite products using the Climate Reference Network (CRN) with more than 110 stations (each with three in situ probes) over USA from 2009 to present. This large number of stations allows for the categorization of SMAP performance based on land cover types, complementing prior efforts based on the few core validation areas with many in situ observations within a single satellite pixel. The SMAP as well as Aquarius products clearly outperform the other products. Over all land cover types, L3SMP, L3SMP-E, and L4SM are better in the summer than in the winter and they perform best over short vegetation. L4SM has higher correlations compared with CRN than L3SMP over tall and short vegetation whereas L3SMP has higher correlations over crops. On average, L3SMP-E performs as well as L3SMP. There is a mismatch between the point in situ measurements and satellite pixel retrievals driven by subpixel precipitation variability, and its impact on these results is also assessed.