An extensive validation experiment of algorithm ZPHI applied to radar HYDRIX

Since September 2004, Hydrix radar has been in operation at the site of ARVALIS-Institut-du-Végétal in Beauce (France), neighbored by a 25-rain gauge network. HYDRIX is a compact X-band polarimetric radar devoted to hydrological applications. Its primary data (radar reflectivity, differential phase shift, differential reflectivity and correlation coefficient) are processed in real time by ZPHI algorithm, to deliver both the rainfall rate R and the DSD intercept parameter N0*. Systematic radar-gauge comparisons have been performed from the beginning of the experiment, providing a large data set with a wide range of rain conditions. While the classical Z-R algorithm provides a very poor estimate as soon as the hourly rain rate exceeds 3 to 4 mm/h, the ZPHI algorithm provides in all circumstances an unbiased estimate with relative statistical error smaller than 25%.