Use of the surface reference technique for path attenuation estimates fromthe TRMM precipitation radar

Estimates of rain rate from the precipitation radar (PR) aboard the Tropica l Rainfall Measuring Mission (TRMM) satellite require a means by which the radar signal attenuation can be corrected. One of the methods available is the surface reference technique in which the radar surface return in rain-f ree areas is used as a reference against which the path-integrated attenuat ion is obtained. Despite the simplicity of the basic concept, an assessment of the reliability of the technique is difficult because the statistical p roperties of the surface return depend not only on surface type (land/ocean ) and incidence angle, but on the detailed nature of the surface scattering . In this paper, a formulation of the technique and a description of severa l surface reference datasets that are used in the operational algorithm are presented. Applications of the method to measurements from the PR suggest that it performs relatively well over the ocean in moderate to heavy rains. An indication of the reliability of the results can be gained by comparing the estimates derived from different reference datasets.