The Estimation of Clear Sky Emission Values from Cloudy Radiometric Data

This report determines the effects of clouds on sidelooking microwave radiometers and develops a technique to adjust cloudy emission values to equivalent clear emission measurements. Clouds of varying liquid water contents and altitudes were used with atmospheres representative of the arctic, mid-latitudes, and tropics. Their effects on microwave brightness temperatures were examined for frequencies between 15 and 55 GHz on a ground-based radiometer viewing at zenith angles from 0 degrees to 89 degrees. The strongest cloud effects were found for low elevation angles at frequencies away from the water vapor and oxygen lines. A technique is proposed which uses cloudy emission measurements made by a scanning two-channel radiometer, and a statistical inversion procedure, to infer equivalent clear emission values.