Comparison of SMOS level 2 and level 3 soil moisture at the SMOSREX site

The ESA (European Space Agency) satellite mission SMOS (Soil Moisture and Ocean Salinity) was launched in November 2009 and has been providing data on ocean salinity and soil moisture over continental surfaces for the last 4 years. SMOS satellite is a passive L-band (1.4 GHz) interferometer that measures the surface soil moisture (top 5cm) with an overpass time at 6 am and 6 pm (local time) and a radiometric resolution of ~ 43 km in average. With a quasi polar orbit, it covers the entire Earth surface in 3 days. The CATDS (Centre Aval de Traitements des Données SMOS) ground segment developed by the French space agency CNES, provides so called “level 3” soil moisture products that are time aggregated products, on the EASE (Equal Area Scalable Earth) Grid with a ~25 km spatial resolution. The retrieval algorithm is based on the radiative model L-MEB (L-band Microwave Emission of the Biosphere). The aim of this paper is to present the different soil moisture products that are delivered by the CATDS such as daily products, 3-day and 10-day composites, monthly averages, discuss different features of the product contents, and also presenting the validation of the SMOS data. Several in-situ sites are equipped with various soil moisture sensors providing soil moisture measurements for different climate areas. For instance, the SMOSREX (Surface Monitoring of the Soil Reservoir Experiment) site was developed to test the SMOS soil moisture retrieval algorithm. Two fields (bare soil and grassland) were monitored with Delta-T theta probes and a cosmic ray neutrons probe that measures the soil moisture over a large area (~ 700m). This site was stopped in 2012 which provides us with more than two years of data that can be compared to SMOS derived soil moisture values