Correcting for radome interference effects on differential reflectivity measurements; implications for operational rainfall estimates

Operational radars with a polarimetric capability have been installed in the UK and France. Analysis of the monthly mean values of differential reflectivity, ZDR, in light rain reveals a reproducible azimuthal variation of 0.4dB peak to peak. The changes in this azimuthal offset from month to month appear to be quite small. It is believed that this interference is due to the construction of the radome or to objects close to the radar. An accuracy of 0.1-0.2dB in ZDR is required for improved rainfall rates, so, unless these azimuthal variations are removed, the prospects for improvements in rainfall estimates using the polarimetric information would appear to be slim.

In this paper the azimuthal variation of ZDR and other polarisation parameters as a function of elevation angle will be analysed in detail, means of correcting for these offsets will be suggested, and an analysis of rainfall rates with and without the azimuthal correction will be presented.