A New Method for Determining Rain Flag of the Sentinel-3 Altimeter

The Sentinel-3 synthetic aperture radar altimeter provides two kinds of rain flag by using the changes of the three backscatter coefficients, which provides a foundation for the comprehensive use of all the backscatter coefficients to determine rain conditions. This paper analyzes the statistical relationship between the two backscatter coefficients of Ku band SAR mode and PLRM mode and the C band backscatter coefficient when it is not rain, then the deviation generated by the backscatter coefficients of the two bands in the rainfall state is compared, provides a new method for determining rain flag. Finally, the measurement data of precipitation radar and altimeter data are matched and verified, and the result of the new method of updating the threshold judgment condition is more accurate.