Multitemporal soil moisture retrieval from 3-days ERS-2 data: Comparison with ASCAT, SMOS and in situ measurements

The use of soil moisture maps derived from satellite remote sensing measurements in operational applications (e.g. hydrology) was generally limited to instruments providing low resolution data (scatterometers, microwave radiometers) so far, because only these instruments offered a suitable temporal resolution. However, with the launch, in 2014, of a new generation of synthetic aperture radar (SAR) systems working at L- and C-bands (i.e., SMAP, Sentinel-1), it is expected the availability of soil moisture maps characterized by high spatial resolution and short revisit time. This kind of data give also the opportunity to improve the quality of SAR-derived soil moisture maps by applying multitemporal inversion techniques that, using a time series of SAR data, allows for dealing with the well-known ill-posedness of the retrieval problem. In anticipation of the availability of Sentinel-1 images, this study uses a dataset of ERS-2 SAR data with a revisit time of only three days to test a multitemporal soil moisture retrieval algorithm, already designed within the framework of project funded by European Space Agency, when vegetation is well-developed. As validation data, the in situ measurements of a set of stations belonging to the International Soil Moisture Network are used. To provide further insights on soil moisture retrieval from satellite microwave data, SAR retrievals and stations measurements are also compared with the estimates provided by ASCAT and SMOS.