2.3.1. SMOS-CESBIO L3 Surface Soil Moisture

The global SMOS L3 SSM product over a 25-km EASE-2 grid was used. The SMOS L3 processor of CESBIO [48] uses the same physically based forward model as the L2 processor [49], with only minor differences that are mainly related to the gridding system. The L3 SSM retrievals are obtained from the SMOS L1C v.620 brightness temperature. On a given day, the L3 algorithm processes several orbits in the same loop. Later, filtering is applied to select the best estimate when several retrievals are available for the same pixel. Therefore, this product is a daily composite of filtered and binned SMOS SSM data [50].

The SMOS-CESBIO L3 SSM is disseminated in separated daily ascending and descending orbits. Similar to the process used for SMAP L4, the area corresponding to the Iberian Peninsula was clipped. Then, a daily average of the ascending and descending orbit maps was applied.
