Retrieval of cloud microphysical parameters from 94-GHz radar doppler power spectra

A technique is presented that uses Doppler spectra collected from a vertically pointing 94-GHz radar to reconstruct cloud and precipitation drop size distributions. A conceptual model describing the broadening of Doppler spectra by turbulence was adapted from earlier works presented in the literature. This model was then used as a basis for an algorithm that solves for parameters describing the turbulence and drop distribution. Numerically simulated Doppler spectra, calculated from known drop distributions, were first used to test the accuracy of the retrieval algorithm. The tests indicate that the retrieval algorithm can accurately retrieve the turbulence parameter and characteristic diameter but is less able to correctly determine the shape parameter. The technique was then applied to actual Doppler spectra collected from a liquid-phase stratus cloud. Vertical profiles of cloud properties such as liquid water content (LWC), effective radius, total number concentration, and mean vertical wind were obtained. The LWC profiles compared well with concurrent aircraft observations both in magnitude and profile shape. Integrated liquid water path agreed with microwave radiometer observations. A discussion is also presented on the limitations of the retrieval algorithm and the feasibility of retrieving cloud microphysical properties in a variety of situations.