Global Estimation of Soil Moisture Persistence with L and C-Band Microwave Sensors

Measurements of soil moisture are needed for a better global understanding of the land surface-climate feedbacks at both the local and the global scale. Satellite sensors operating in the low frequency microwave spectrum (from 1 to 10 GHz) have proven to be suitable for soil moisture retrievals. These sensors now cover nearly 4 decades thus allowing for global multi-mission climate data records. In this paper, we assess the possibility of using L-band (SMOS) and C-band (AMSR2, ASCAT) remotely sensed soil moisture time series for the global estimation of soil moisture persistence. A multi -output Gaussian process regression model is applied to ensure spatio-temporal coverage of the satellite data sets. It allows a robust computation of temporal autocorrelation and e- folding times. Results over a selection of catchments reveals general agreement between the response of in-situ and satellite microwave observations to hydrological processes. The response of the uppermost-modeled soil moisture layer of GLDAS-1- Noah agrees well with that of the observations, whereas major differences are displayed by MERRA2 reanalysis. The temporal dynamics of the three microwave sensors are shown to be consistent, close to in-situ and to GLDAS-1- Noah, which supports their combination for the global estimation soil moisture persistence.