The use of simultaneous horizontal and vertical transmissions for dual-polarization radar meteorological observations

Observations have been obtained in which standard dual linear-polarization quantities (Z_DR, phi_DP, and rho_HV) are determined from simultaneous H and V transmissions, measured in parallel H and V receiving channels. This approach represents an optimal way of making dual-polarization measurements; it has the advantage over alternating H and V transmissions that the measurements are not contaminated by the interpulse Doppler shifts and are speeded up by a factor of two or more by not having to alternate between polarizations. In addition, a high power polarization switch is not needed and is replaced by a simple power divider. For the studies of this paper, conducted in the summers of 1998 and 1999, the relative phases of the H and V components were adjusted so that the transmitted polarization was circular. Circular polarization optimally detects the presence of randomly-oriented or randomly-shaped particles and can also be used to determine the orientation angles of aligned particles such as ice crystals. The time saved by not having to transmit alternate H and V signals can be used make true polarization diverse measurements, for example by alternating between circular and slant 45 linear transmissions, or between RHC and LHC polarizations.