Determination of Cloud Liquid Water Distribution by Inversion of Radiometric Data

Abstract

A method is described whereby the distribution of liquid water through a cross section of a cloud may be determined from radiometric data. It involves the scanning of the cloud by a pair of ground-based centimeter wave radiometers and measuring the emission from a multiplicity of different directions. The time required to obtain all of the necessary information should be less than three minutes. The emission is sensibly independent of the presence of ice in the cloud and depends essentially upon the integrated liquid water content along the path. Corrections need to be made for the mean temperature and water vapor profiles in the cloud and the clear air environment. If there is significant water content in drops larger than about 1 mm diameter the emissivity becomes drop size dependent, so the technique is useful only in the preprecipitation phase of cloud development or before the rain rate reaches about 1 mm h?1. The distribution of liquid water is determined by mathematical inversion procedures. Simulation studies suggest that the technique should be capable of yielding the liquid water content to within about 10% of the maximum water content within the cloud with a spatial resolution of a few hundred meters.