2.3.2. SM2RAIN-ASCAT

The SM2RAIN algorithm was applied to three surface SM products obtained from Advanced Microwave Scanning Radiometer for Earth Observing (AMSR-E), Soil Moisture and Ocean Salinity (SMOS), and Advanced SCATterometer (ASCAT) to develop the SM2RAIN-ASCAT dataset [9]. ASCAT is a scatterometer and consists of the space segment of the EUMETSAT Polar System (EPS), operating at 5.255 GHz (C-band VV polarization) onboard MetOp A, B, and C satellites [55]. The spatial resolution of SM2RAIN-ASCAT is the same as the parent ASCAT SM dataset (previously developed datasets were resampled to spatial resolutions of 0.5◦ and 1◦). SM2RAIN-ASCAT has 12.5 km spatial and daily temporal resolutions available for the period 2007–2018 [46]. The SM2RAIN-ASCAT showed more accuracy when evaluated on the basis of root mean square error (RMSE), Pearson correlation coefficient (R), and detection of precipitation [9].

The main differences between SM2RAIN-CCI and SM2RAIN-ASCAT datasets are the input SM datasets (input products for SM2RAIN-CCI are the ESA CCI SM product [56], and the time span of SM2RAIN-CCI that is available, namely, the period of 1998–2015). Moreover, the SM2RAIN-ASCAT is bias-corrected and calibrated against the Medium-Range Weather Forecasts (ERA5) instead of GPCC-FDD as SM2RAIN-CCI [43,46]. In the current study, version 1.0 of SM2RAIN-ASCAT, released in March 2019, is used.
