Estimating Mean Surface Backscatter from GPM Surface Backscatter Observations

The radar on the Global Precipitation Measurement (GPM) mission observes precipitation at 13.4 GHz (Ku-band) and 35.6 GHz (Ka-band) and also receives echoes from the earth’s surface. These surface measurements are important to GPM for estimating the path-integrated attenuation in precipitation. For land, a measurement of the surface in rain is compared with prior measurements of the same location under non-raining conditions. These prior measurements are stored in a database; in doing so, there is a trade between space and time resolution and number of samples. One of the goals of this paper is to investigate variation of surface backscatter in both time and space to understand how to best construct the database. The author finds that due to inhomogeneity of backscatter in time, increased time averaging can increase measurement standard deviation. This is similar to the effect of spatial averaging noted by Meneghini and Jones (2011). Spaceborne precipitation radar has also been used previously for monitoring of surface water and vegetation. A second goal of this paper is to further investigate this application, using GPM dual-frequency backscatter to perform a global classification.