Potential operational performance of rainfall algorithms using polarisation radar

Errors in the estimates of rainfall from observations of radar reflectivity with conventional radars can potentially be reduced by the use of polarisation techniques. Both differential reflectivity and differential phase shift essentially depend upon the fact that oblateness of raindrops increases with size. However, the polarisation signatures are quite small and we show that it is difficult to achieve the desired accuracy at each radar gate for the dwell times associated with a radar scanning at the rate needed for an operational system. Instead we suggest that there are various integral polarisation parameters which can be accurately estimated along the radar path, and that these integral properties can be used as a constraint which can be used to improve the accuracy of rainfall estimates.