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. During the 2004 Winter Icing and Storm Project (WISP04) research radars and radiometers were deployed at NCAR’s Marshall experimental site in Boulder, Colorado to evaluate remote sensing techniques for characterizing cloud icing conditions. The dataset includes Ka-band radar reflectivity and two-channel radiometer liquid water path (LWP) measurements. In this paper, we present results of retrieved cloud microphysical characteristics using these remote measurements.

Cloud LWC and RES are retrieved from the radar and radiometer measurements using (1) the Hitschfeld-Bordan attenuation correction method and (2) the constrained-gamma cloud drop size distribution (DSD) model. The Hitschfeld-Bordan method uses an attenuation-reflectivity power-law relation and adjusts its coefficient with path integrated attenuation (PIA) derived from radiometer measurements. The constrained-gamma cloud DSD method retrieves gamma DSD parameters from radar reflectivity and the PIA. A constant scale parameter (N0) and either a constraining relation between the shape (µ) and slope parameter (Ë) or a fixed µ are assumed. Retrieved cloud LWCs and RESs using the two methods are in good agreement. The retrievals are verified with in-situ aircraft measurements and are in reasonable ranges. The severity of cloud icing conditions can be inferred from spatial distributions of the retrieved cloud LWCs and RESs.