Ice crystal size estimation using multiple-wavelength radar

Measurements and simulations of multiple-wavelength radar scattering have demonstrated the feasibility of using multiple-wavelength systems to estimate effective hydrometeor size in ice-phase clouds, and in various forms of precipitation. Radar reflectivity differences occur when the higher frequency experiences non-Rayleigh scattering. For cloud particle sizing, the higher frequency must exhibit non-Rayleigh scattering from small hydrometeors. This occurs at mm-wavelengths where radar systems typically operate in one of several atmospheric transmission windows centered near 35 GHz, 95 GHz, 140 GHz and 215 GHz. The authors present realistic electromagnetic simulations of scattering from ice crystals and spheres that show the importance of ice crystal shape and orientation effects for particle sizing and for calibration. While simulation results show that shape and orientation effects are significant for larger particles they can be neglected for distributions of small, Rayleigh-scattering particles. This implies that calibrations are insensitive to particle shape and orientation.