Monitoring multi-decadal satellite earth observation of soil moisture products through land surface reanalyses

Soil moisture from ERA-Land, a revised version of the land surface components of the European Centre for Medium-Range Weather Forecasts Interim reanalysis (ERA-Interim), is used to monitor at a global scale the consistency of a new microwave based multi-satellite surface soil moisture date set (SM-MW) over multi-decadal time period (1980–2010). ERA-Land results from Land Surface Model simulations forced by high quality atmospheric forcing data. It was shown to adequately capture the temporal dynamic of soil moisture. ERA-Landʹs large scale nature, frozen configuration, global availability and ability to accurately represent soil moisture variability make it suitable to complement typical validation approaches of soil moisture from remote sensing based on ground measurements. Considering locations that have significant correlations for each 3-year sub periods within 1980–2010, averaged soil moisture correlations of SM-MW with ERA-Land (at 95% Confidence Interval) are increasing steadily from 1986 to 2010 (from 0.52 ± 0.10, to 0.66 ± 0.04). The lower correlations mirror the periods where only passive microwave from the Special Sensor Microwave/Image (SSM/I, Ku band at 19.3 GHz) sensor was used, highlighting the importance of multi-sensor capabilities. Overall SM-MW is relatively stable over time with respect to ERA-Land. Good agreement is obtained in semi-arid areas, whilst the tropics and high latitudes (and altitudes) present lower correlations values.