Mapping bragg scatter with a polarimetric WSR-88D

Using a polarimetric Weather Surveillance Radar-1988 Doppler (WSR-88D) radar to distinguish Bragg scatterers from insects and birds in an optically clear atmosphere has the potential to provide information on convective boundary layer depth. Measured median differential reflectivities Z_DR of Bragg scatterers lie between 20.08 and 0.06 dB, which supports the hypothesis that the intrinsic Z_DR of Bragg scatters is 0 dB. Thus, the intrinsic 0 dB of Bragg scatter can be used for verifying of Z_DR radar calibration. Measured copolar correlation coefficients rhv have distributions peaked at about 0.998-1.0. If insects and birds are spatially separated from Bragg scatterers, the dual-polarization capability of the WSR-88D allows distinguishing echoes from these two types of scatterers since Z_DR from biota is significantly larger than 0 dB. In mixtures of Bragg and biota scatter, polarimetric spectral analysis shows differences in portions of the H and V spectra where birds and insects could be contaminating echoes from Bragg scatterers. The values of Z_DR≈ 0 and ρhv≈ 1 that characterize Bragg scatterers allow coherent summation of signals from the H and V receiver channels and restoration of measurement capability lost as a result of splitting power into H and V channels. Further enhancements to data collection and signal processing allow power measurement, with a standard deviation of about 1 dB, of weak echoes from Bragg scatterers having equivalent reflectivity factors of about-28 dBZ at distance of 10 km from the radar. This level of reflectivity corresponds to a refractive index structure parameter C²_n of about 43×10^-15 m^-2/3, a typical magnitude found in maritime air.