Simulations of Polarimetric Bistatic Scattering at Multiple Frequencies

Polarimetric bistatic radars could potentially provide novel radar measurements at a low unit cost, enabling unique microphysical retrievals concurrently with 3D wind retrievals. The recent development of a low-cost passive bistatic weather radar network at the University of Oklahoma's Advanced Radar Research Center (ARRC) has enabled effective bistatic weather observations at vertical polarization. Given the two available channels per receiver, further enhancement of the network to dual polarization is planned. However, little is known about the nature of bistatic polarimetric radar variables, particularly in non-Rayleigh scattering regimes. A time-series simulator for polarimetric monostatic and bistatic radar configurations has been developed to investigate the general tendencies of polarimetric bistatic radar variables (Zdr, ρhv, etc.) in simulated weather events. The simulator employs T-matrix scattering calculations applied to PSDs of rain and varying hail types, allowing for highly detailed simulations of bistatic radar variables. This level of detail places an emphasis on the microphysical scheme within the cloud model used for the meteorological input data, in this case Cloud Model 1 (CM1). Simulations of supercell thunderstorms in CM1 with the Morrison and NSSL 2-moment microphysics schemes are observed by a series of simulated multistatic weather radar networks at S-, C-, and X-band frequencies, with a network layout optimized for multi-Doppler retrievals on a storm-scale level. Generally, bistatic ZDR is found to be usable for discriminating between rain and hail regimes, especially when the bistatic scattering angle is considered. Differences between the two microphysical schemes manifest primarily through variations in the size and spatial distributions of hail, which have great implications for the observed bistatic radar moments. In terms of frequency, S-band appears to be the most effective for rain/hail discrimination, followed by C- and X-band, due to increasing variability in scattering amplitudes at most bistatic scattering angles near horizontal incidence.