Studies have shown that a combination of supercooled liquid water (SLW) content and droplet size contributes to accretion on an aircraft surface. The accretion of SLW onto an aircraft surface is defined as icing. Remote measurement of liquid water content (LWC) and mean droplet size are essential for quantifying icing severity. Icing severity of a single-phase cloud consisting of small cloud droplets can be quantified easier than in the case of a mixed phase cloud containing liquid and ice particles. Recent in situ aircraft observations in dicate that more than 60% of icing clouds are mixed phase. In most of the mixed phase clouds, mean ice particle size is an order of magnitude larger than droplet size and hence ice particles enhance radiation measured by the ground-based radiometer through scattering of the emission from vapor, liquid, and atmospheric gases.

This paper studies the scattering effects of ice particles on ground-based multi-frequency microwave radiometer measurements. A microwave radiation transfer model for calculating brightness temperature of a mixed-phase cloud is developed. The brightness temperature is calculated based on the rigorous radiation transfer model for clouds with or without ice particles present. The enhancement of the radiation due to ice particles is studied as a function of ice water path (IWP) and ice particle size. It is found that enhancement in down-welling radiation is a sensitive function of mean particle size. The temperature and vapor profiling as well as liquid water retrieval are all affected by enhanced scattering of ice particles. An approach for quantifying enhanced radiation due to ice scattering is proposed and also a method for improving the accuracy of temperature, vapor, and liquid profiling using K and V-band microwave radiometer is investigated.