Estimation of cloud droplet size and liquid water content using dual-wavelength radar measurements

Transmitted radiation at W or K/sub a/-band is measurably attenuated by liquid water whereas at X-band is not; the range-differentiated difference between the returned signal is proportional to the amount of liquid present. The liquid water retrieval is confounded by the presence of hydrometeors, either ice or liquid, in the Mie-scattering size range (where the particle diameter is comparable to the radar wavelength). A dual-wavelength system consisting of Xand K/sub a/-bands is best suited for ground-based remote sensing of mixed-phase clouds. Factors such as Mie scattering, shallow clouds, and sensitivity of the X-band radar limited the LWC retrieval. A combination of detailed numerical simulations with radar and radiometer data demonstrated the feasibility of a dual-wavelength system for derivation of range-gated LWC along the beam path under a variety of realistic atmospheric conditions and suggested a technique for determining the presence of Mie scatterers. In this study, tri-frequency radar (X, K/sub a/, W-band) measurements collected during MWISP (Mount Washington Icing Sensors Project) were analyzed. Three different data sets exhibit distinct scattering characteristics: (a) Rayleigh scattering, (b) Mie scattering at W-band, and (c) Mie scattering at both W and K/sub a/-bands. The liquid water path estimates along the radar beam are compared with collocated microwave radiometer measurements. In addition, spatial and temporal variations in LWC and droplet size are retrieved.