The Use of Simultaneous Horizontal and Vertical Transmissions for Dual-Polarization Radar Meteorological Observations

Richard D. Scott, Paul R. Krehbiel, and William Rison

Abstract:

Observations are presented in which standard dual-polarization meteorological parameters (e.g., $Z_{\rm DR}$, $\phi_{dp}$, and $\rho _{HV}$) are determined from simultaneous horizontal (H) and vertical (V) transmissions. The return signals are measured in parallel H and V receiving channels. Because the parameters are determined from simultaneous measurements they are not affected by Doppler phase shifts that increase the variance of measurements from alternating H and V transmissions. The approach has the additional advantage that a high-power polarization switch is not needed. The relative phases of the H and V components were such that the transmitted polarization was circular. Circular polarization is shown to be optimal for detecting randomly oriented particles such as hail, and detects horizontally oriented particles such as rain with the same effectiveness as linearly polarized transmissions. A geometric description is presented of the depolarization caused by different classeclasses of scatterers, based on the Poincaré sphere representation of the polarization state. The description provides a simple way of understanding the various depolarization effects and of determining the relative advantages of transmitting different polarizations. By not having to transmit alternate H and V signals it becomes practical to make polarization-diverse measurements by transmitting independent polarizations, for example LHC and H or LHC and $+{45^\circ}$ slant linear, on alternate pulses to aid in identifying precipitation types.