Radar/radiometer combination to retrieve cloud characteristics for icing detection

Remote measurements of cloud liquid water content (LWC) and characteristic droplet size (e.g., radar estimated size: RES) are required for quantifying potential aircraft icing hazard (Politovich, 1989; Politovich and Bernstein, 2002; Vivekanandan et al., 2001). During the 2004 Winter Icing and Storm Project (WISP04), research radars and radiometers were deployed at NCAR’s Marshall experimental site near Boulder, Colorado to evaluate remote sensing techniques for characterizing cloud icing conditions. The dataset included radar and radiometer measurements. The best case for single wavelength radar and twochannel radiometer-based retrievals was on March 1011, when a shallow, fairly uniform stratus cloud in the temperature range of ~ -5 to -15C was observed. High liquid water content and little ice was found in the cloud. This cloud began with some patches of relatively high reflectivity (~10-20 dBZ) and snow showers at the ground. It then evolved to low (<-10 dBZ) reflectivity with lots of liquid, as evidenced by numerous pilot reports of icing in the Denver area. Strong ground clutter at S-band limits the usefulness of the data for a dual-wavelength application. Nevertheless, Ka-band radar reflectivity and radiometer measurements were available for retrieving cloud characteristics. In this paper, we present retrievals for cloud LWC and RES from single frequency radar reflectivity and dual-channel radiometer measurements. Retrieval methods are reviewed in Section 2. The retrieval results and comparisons are presented in Section 3. A summary and discussion are given in Section 4.