The polarization characteristics of randomly oriented nonspherical ice particles in mm and sub-mm frequency range: Implications to the remote sensing of cirrus clouds using satellite microwave radiometry

The depolarization effects of randomly oriented nonspherical ice particles are studied for frequencies ranging from 90 to ~900 GHz. It is found that, given the particle shape and the working frequency, the brightness temperature difference between the vertical and the horizontal polarization measured by a space-borne radiometer is only sensitive to ice particles of sizes within a certain range. The center of this range moves from >1000 μm to ~120 μm for nearly spherical particles when the frequency changes from 90 to 874 GHz. The particle size given here is the median mass equivalent sphere diameter. This range also changes with the particle shape. Generally, particles with a greater aspect ratio show a stronger depolarization effect by larger sizes. These features suggest that radiometric measurements from satellite on the polarization difference may be useful in determining ice particle size and shape in the cirrus clouds