Bias in Copolar Correlation Coefficient Caused by Antenna Radiation Patterns

Abstract

We present a theoretical study of the bias in the copolar correlation coefficient (ρ hv ) caused by cross-polar radiation patterns and by unmatched horizontal and vertical copolar radiation patterns. The analysis of the bias induced by crosspolarization radiation is carried out for both modes of operation of polarimetric radars, designated as the simultaneous transmission and reception of horizontally and vertically polarized waves and the alternate transmission of horizontally and vertically polarized waves, respectively. The bias caused by unmatched horizontal and vertical copolar radiation patterns as a function of slight differences in pointing angles and beamwidths is also analyzed. In well-designed weather radars, for the purpose of hydrometeor classification, the overall acceptable bias in the copolar correlation coefficient should be less than about 0.01. The levels of crossto-copolar gain ratios for acceptable performance are indicated. Ultimately, pointing angle and beamwidth tolerances are indicated for horizontal and vertical copolar antenna patterns.

A Unified Formulation of Polarimetric Weather Radar With Application to IQ Data Simulation

“…in [19]. This maximum value of the bias of the copolar correlation coefficient occurs for zero phase shift between copolar radiation patterns, zero phase shift between co and cross-polar radiation patterns, and negligible propagation effects, that is, zero differential phase shift.…”

“…Second, copolar and cross-polar antenna radiation patterns are taken into account in order to validate the main contribution of the method proposed, that is, that antenna effects can be decoupled from scattering effects. For that, polarimetric parameters obtained from simulated data considering copolar and cross-polar radiation patterns are compared to polarimetric variables analytically obtained in [19] and [20]. In [19], the bias of the copolar correlation coefficient caused by cross-polar radiation, for the SHV mode, is analytically calculated.…”

“…For that, polarimetric parameters obtained from simulated data considering copolar and cross-polar radiation patterns are compared to polarimetric variables analytically obtained in [19] and [20]. In [19], the bias of the copolar correlation coefficient caused by cross-polar radiation, for the SHV mode, is analytically calculated. In [20], the bias of the differential reflectivity due to cross-polar radiation is obtained, also for the SHV method.…”

“…Bias of the copolar correlation coefficient for the SHV mode due to cross-polar patterns. Ideal Gaussian coaxial copolar and cross-polar antenna patterns have been assumed Continuous lines: maximum value of the bias of the copolar correlation coefficient [19]. Dotted lines: estimated bias from simulated data.…”

Correction of polarization error in scanned array weather radar antennas

“…It's desirable to form a very narrow beam because of the distributed characteristic of meteorological targets. Nevertheless, for a mechanically scanning weather radar, a narrow beam still has considerable impacts on cross-polar measurements [2]- [6]. Moreover, for a phased array weather radar, it's inevitable that the beam will be expanded while scanning, which means the impacts of limited beamwidth will be emphasized when the beam is off broadside.…”