Multi-frequency and Polarization Radar-Based Detection of Liquid Droplets

Preliminary results of dual-wavelength radar data analysis and model calculations show the potential for detecting liquid water content and droplet size. However, the dual-wavelength technique is susceptible to non-Rayleigh scattering effects, mixed-phase precipitation, and sampling volume differences between two radars. Only a limited verification of the technique is presented in the previous studies by comparing liquid water path along the radar beam with the corresponding microwave radiometer-based liquid path retrieval. In the absence of in situ aircraft measurements, it is difficult to verify dual-wavelength-based liquid water content estimate and droplet size. This limitation can be partially eliminated in the case of tri-frequency (X, Ka, and W-band) measurements because two independent liquid water estimates can be derived using X and Ka pair and Ka and W-band pair observations.

In this paper, tri-frequency radar measurements collected during the Mount Washington Icing Sensing Project (MWISP) were analyzed. The retrieved liquid water contents and droplet sizes were compared. The estimated liquid water path is compared with radiometer observation. The attenuation corrected dual-wavelength ratio at X/Ka and Ka/W were used for estimating particle size. The MWISP data analysis suggest the dual-wavelength technique is limited by a number of radar performance factors such as, (a) sensitivity of X- and W-band radar systems, (b) fluctuation in reflectivity measurements, and (c) sampling volume differences between radars. The paper suggests preliminary specification for an optimal radar system for liquid water content and droplet size estimations.