An assessment of SMOS version 6.20 products through Triple and Quadruple Collocation techniques considering ASCAT, ERA/Interim LAND, ISMN and SMAP soil moisture data

In this work, two remotely sensed soil moisture data sets, derived by the Advaced SCATterometer (ASCAT) and the Soil Moisture Ocean Salinity (SMOS), have been compared with the soil moisture provided by the ERA/Interim Land data sets and measured by the in situ probes belonging to the International Soil Moisture Network (ISMN). The Triple Collocation (TC) represents a very useful tool for validating remotely sensed products; in this work, since four sources have been considered, a Quadruple Collocation (QC) approach has been also applied in order to jointly estimate the error standard deviation of the four sources making reference to a common scale as for its magnitude. Both Europe and North Africa were considered during a period starting from June, 2010 to May, 2014. Moreover, the preliminary results of a TC analysis between SMOS, ASCAT and SMAP (Soil Moisture Active/Passive) soil moisture products are shown for the same region of interest considering a period between April and December, 2015.