Cloud liquid water content and particle size retrievals using dual-wavelength radar measurements

A technique for estimating liquid water content (LWC) using simultaneous dual-wavelength radar observations is proposed and tested. The method takes advantage of the differential liquid water attenuation of the two wavelengths. This is accomplished by comparing the power returned from a non-attenuated wavelength (S-band, 10 cm) and an attenuated wavelength (Ka-band, 8 mm) to estimate the liquid water attenuation values of the Ka-band wavelength. The estimates are over radar ray segments that are long enough to result in a measurable attenuation signal, typically about 2 km. The total attenuation over the ray segment is then apportioned to the radar range resolution (150 m) using the S-band reflectivity. The LWC is computed from the Ka-band liquid water attenuation estimates. An important advantage to this technique is that the Ka-band liquid water attenuation is directly related to LWC without any dependence on the drop size distribution, a unique property of this wavelength.

The estimated LWC data can then be used to estimate the median volume diameter (MVD) and the radar estimated size (RES). The preliminary LWC, MVD and RES retrievals compare well to aircraft probe measurements. This paper will present the proposed retrieval method, and show examples from the Rain In Cumulus over the Oceans (RICO) and Refractivity Experiment for H2O Research and Collaborative Operational Technology Transfer (REFRACTT) field experiments.