Multi-frequency radar Doppler spectrum measurements of cirrus clouds

Improved remote sensing of cirrus cloud particle size and ice mass content is important for validating and improving cloud microphysical models used in climate research. Previous radar studies have shown that cloud particle size can be derived from non-Rayleigh scattering effects at 95 GHz (W-band) using dual-frequency radar. Typically, non-Rayleigh scattering is quantified by comparing 95 GHz Doppler spectra moments to those collected at a second lower frequency such as 35 GHz (Ka-band). The ratio of 95 GHz reflectivity to that at the lower frequency is referred to as the dual wavelength ratio (DWR). Scattering models relate DWR to median volume diameter or some other characteristic size parameter. However, analysis of full Doppler spectrum measurements collected at 33 GHz and 95 GHz reveals additional information from which vertical air motion and parameters of the particle size-velocity relationship can be retrieved. During 2000, the U.S. Department of Energy Atmospheric Radiation (DOE-ARM) Program sponsored the 2000 Cloud Intensive Operations Period (2000 Cloud IOP). A number of unique remote and in situ sensors participated in the IOP, including the University of Massachusetts dual-frequency Cloud Profiling Radar System (CPRS). CPRS operates simultaneously at 33 GHz and 95 GHz through a single one-metre-diameter dielectric lens antenna, which ensures beam co-location. Both the Ka-band and W-band recorded fast Fourier transform measurements of the full Doppler spectrum at vertical incidence