Differential Reflectivity (ZDR) calibration for CASA radar network using properties of the observed medium

The Center for Collaborative and Adaptive Sensing of the Atmosphere (CASA) has deployed a Distributive, Adaptive and Collaborative Sensing (DCAS) network of four radars in central Oklahoma working as a closed-loop system since 2006. The radars operate at the X-band frequency and are capable of polarimetric and Doppler measurements. The radar network is being evaluated for Quantitative Precipitation Estimation (QPE). QPE algorithms based on radar power measurements (e.g. Z_H and Z_DR) require bias correction. Z_DR calibration is required prior to any application of the self-consistency principle. Two different methods were evaluated for Z_DR bias correction. The intrinsic properties of dry aggregated snow present above the melting layer and light rain measurements close to the ground are used for the study. Results show a Z_DR calibration accuracy of 0.2 dB or less for both analyzed events when both methods are compared.