Brocca, Luca; Massari, Christian; Ciabatta, Luca; Wagner, Wolfgang; Stoffelen, Ad, 2016, Remote Sensing of Terrestrial Rainfall from Ku-Band Scatterometers, IEEE journal of selected topics in applied earth observations and remote sensing (Print) 9 (2016): 533–539. doi_10.1109/JSTARS.2015.2508065,
URL: http://www.cnr.it/prodotto/i/358465

Rainfall is the most fundamental variable of the terrestrial hydrological cycle. However, in many regions of the world, ground observations are still very scarce or even missing. Recently, a bottom-up approach, named SM2RAIN, for terrestrial rainfall estimation from satellite soil moisture (SM) products was proposed and successfully applied to C-and L-band products from scatterometers and radiometers. Thanks to the multiple Ku-band scatterometers launched in the recent years and a number of new sensors expected in the near future, accurate rainfall estimation at subdaily time scale could be obtained. We present here a first attempt to estimate terrestrial rainfall from Ku-band scatterometers using SM2RAIN. To this end, backscattering data (sigma-0) collected in central Italy from the RapidScat instrument on board the International Space Station are compared with the Advanced SCATterometer (ASCAT, C-band) SM product and in situ observations for assessing its sensitivity to SM variations. Then, RapidScat sigma-0 is used for rainfall retrieval and compared with ground observations over a regular grid of 15-km spacing. The 8-month period from Nov 2014 to Jun 2015 is considered. Results show a very good agreement between ASCAT SM and RapidScat SM index with a median temporal correlation coefficient R of ~0.9 and a reasonable performance (R > 0.52) against in situ data. More interestingly, the performance of RapidScat in 1-day rainfall estimation is found to be satisfactory with median R-values equal to ~0.6. These promising results highlight the large potential of using the constellation of scatterometers for providing an accurate rainfall product with high spatial-Temporal resolution.

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