Cirrus Cloud Studies with Elliptically Polarized Ka-band Radar Signals: A Suggested Approach

Abstract

It has been shown previously that the use or elliptically polarized radar signals can help to obtain polarization signatures from tenuous cirrus clouds. Estimates of particle dimension ratios and orientations can be made in situations where conventional circular and linear polarizations fail because of weak echoes in one of the received polarization channels. One way of achieving elliptical polarizations is to install a quarter wave plate before the radar transmitter. This paper introduces two new easily measurable elliptical polarization parameters. These parameters are 1) the depolarization ratio for elliptical polarizations that slightly differ from the circular polarization, and 2) the difference in quarter wave plate angular positions that provide equal returns in both received polarization channels. The use of the elliptical depolarization ratio increases echo in the ?weak? channel without significant change of echo in the ?main? channel. This ratio is used to estimate ice particle deformity (deviation from sphericity). The second suggested parameter can be measured during continuous rotations of the quarter wave plate. It can be used to estimate the combined effect of the degree of common alignment of the ice crystals and their deformity. Operational procedures and possible data interpretations are discussed with emphasis on cloud sensing with Ka-band radar.