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

Abstract

Observations are presented in which the standard dual-polarization meteorological quantities (ZDR, ?dp, and ?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 ?dp and ?HV when alternating H and V polarizations are transmitted. 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 detect horizontally oriented particles such as rain with the same effectiveness as linearly polarized transmissions, and optimally detects randomly oriented or shaped particles such as hail. Circular polarization also optimally senses nonhorizontally oriented particles such as electrically aligned ice crystals. By not needing to alternate between H and V transmissions it becomes practical to make polarization-diverse measurements by transmitting other orthogonal polarizations on successive pulses (e.g., left-hand circular and +45° slant linear) to aid in identifying precipitation types. It is shown that ?HV from simultaneous transmissions provides the same information on randomly oriented scatterers as the linear depolarization ratio LDR from H or V transmissions, and that LDR does not need to be measured when information on particle canting is not important or is not needed.