An Assessment of Droplet Size and Liquid Water Content Derived from Dual-Wavelength Radar Measurements to the Application of Aircraft Icing Detection

Multiple parameters are needed to adequately describe the icing condition of clouds, yet those that can be accurately measured using remote sensors are usually limited. In this paper, a detection and classification method using two parameters derived from dual-wavelength (Ka and X bands) radar measurements is explored. The first of these is the radar-estimated size (RES), defined as the cube root of the sixth and third moment size distribution ratio. The RES is shown to be useful in characterizing icing environments through simulations using modified gamma droplet size distributions with realistic bounds based on several sets of in situ measurements. The RES is also relatively easy to retrieve using dual-wavelength radar measurements. The second parameter is the liquid water content (LWC), the total mass of liquid droplets of all sizes. The LWC may be estimated by taking advantage of the difference in attenuation due to the presence of liquid water between the X- and Ka-band radars. In situ measurements of droplet spectra in various research projects were analyzed for quantifying the utility of LWC, RES, and median volume diameter for describing aircraft icing hazard categories. It is shown that a combination of RES and LWC could distinguish environments with a combination of large droplets and higher liquid water contents.