Bright Band Errors in Radar Estimates of Rainfall: Identification and Correction Using Polarization Diversity

Abstract

A principle source of error in rainfall rates derived from the radar reflectivity (Z) is caused by the enhanced radar return due to melting snowflakes in the bright band. We present observations of two S-band polarization radar parameters which enable the bright band to be simply identified. The technique involves transmission of horizontally and vertically polarized radiation and reception of the co-polar and cross-polar return signals. The linear depolarization ratio (LDR) is defined as the ratio of the cross-polar to the co-polar return and p(H,V) as the correlation of the time series of the horizontal and vertical co-polar return. The high values of Z in the bright band are accompanied by values of LDR above -18dB and p(H,V) below 0.8. In echoes where no bright band is present the values cf LDR are everywhere below -20dB and the correlation is always close to unity. We discuss potential problems in implementing these techniques for C-band radars with one degree beamwidths, and also consider how they could be used to identify spurious echoes from ground clutter and anomalous propagation.