Bias in Differential Reflectivity due to Cross Coupling through the Radiation Patterns of Polarimetric Weather Radars

Examined is bias in differential reflectivity and its effect on estimates of rain rate due to coupling of the vertically and horizontally polarized fields through the radiation patterns. To that end, a brief review of the effects of the bias on quantitative rainfall measurements is given. Suggestions for tolerable values of this bias are made. Of utmost interest is the bias produced by radars simultaneously transmitting horizontally and vertically polarized fields, as this configuration has been chosen for pending upgrades to the U. S. national network of radars (Weather Surveillance Radar-1988 Doppler; WSR-88D). The bias strongly depends on the cross-polar radiation pattern. Two patterns, documented in the literature, are considered.