Differential Phase on Transmission

In the simultaneous transmission and simultaneous reception mode for polarimetric weather measurements, the difference in phase between the horizontally and vertically transmitted waves β determines the polarization of the composite wave. Knowledge of β is needed to a) estimate the depolarization ratio and b) compute errors in some polarimetric variables. We propose estimating β from returns off the melting layer. A sharp change of the differential phase observed at vertical incidence in the melting layer is entirely due to the differential phase on transmission (β). Its root cause is coupling between the Horizontally (H) and Vertically (V) polarized components of the impinging electric field. We hypothesize that a similar change would occur in returns from other scatterers exhibiting a low correlation coefficient between the H and V polarized components.
We compare the transmitted differential phase estimates from data of the 3- cm wavelength radar operated by the OU Advanced Radar Research Center, designated as PX-1000, with the instrumented measurement. The enabler of this measurement is the capability to vary the transmitted differential phase on the PX-1000. Further, we explore estimation of β at pointing directions 30 to 40 degree off zenith aiming to apply the methodology to radars that have upper limit in beam pointing, like the WSR-88Ds.