Global assessments of two blended microwave soil moisture products CCI and SMOPS with in-situ measurements and reanalysis data

Abstract Multiple soil moisture (SM) products have been produced based on observations from microwave satellite sensors nowadays, allowing for the acquisition of global SM dynamics in a timely manner. Currently, only two blended microwave SM products, namely the Climate Change Initiative (CCI) from the European Space Agency and the Soil Moisture Operational Product System (SMOPS) from the National Oceanic and Atmospheric Administration, are available with either better temporal or better spatial coverage than those of other SM products derived from a single sensor. However, an assessment and especially a synchronous comparison of these two products are still lacking, making it difficult to determine a better alternative in actual applications. In the present study, a comprehensive assessment of the two blended products was conducted with reanalysis SM data from the European Centre for Medium-Range Weather Forecasts and in-situ measurements from the International Soil Moisture Network. The scaling strategy of cumulative distribution function matching was used to remove the systematic differences in spatial mismatch between the satellite pixels and ground in-situ observations. The results indicated that CCI reveals overall better accuracy than that of SMOPS with both in-situ measurements and reanalysis data under different climate patterns. Specifically, the overall root mean square error (RMSE) with the in-situ measurements were 0.042 m3/m3 and 0.046 m3/m3 for CCI and SMOPS, respectively. Further investigation also confirmed that SMOPS could be a potential alternative over the regions where CCI is not available, since SMOPS has better spatial coverage than CCI.