Quantitative Measurements of Path-Integrated Rain Rate by an Airborne Microwave Radiometer over the Ocean

Abstract

Data on the airborne microwave radiometer, which is one of the sensors of the airborne microwave rain-scatterometer/radiometer (AMRS) system, are analyzed to infer path-integrated rain rate measured from topside. The equation of radiative transfer is used to relate quantitatively the antenna temperature to the rain rate profile inferred by the scatterometer. The influence of the ocean surface temperature on the radiometer measurements of rain is evaluated by a model computation. The theoretical prediction agrees excellently with the measurements. The effect of nonuniform rain along the propagation path is also evaluated by using the experimental data. It is shown that the excess antenna temperature (difference between the antenna temperature under raining and no-rain conditions) in the 10 GHz band is proportional to the path-integrated rain rate, and a method for determining the reference temperature (antenna temperature under a no-rain condition) is suggested.