Optimizing quantitative precipitation estimates using a noncoherent and a coherent radar operating on the same area

A 40 hour period of rainfall during the 1994 Piemonte flood is analyzed; da ta from 69 rain gages were considered as well as 5 min maximum reflectivity maps acquired by an old, noncoherent radar and a "new-generation" Doppler one. The two C-band radars share a similar, hostile radar detection environ ment: the good view from the radar sites produces severe ground clutter con tamination in an adverse orography. Furthermore, we are working at long ran ges (distances between radar and gages up to 214 km). The data of both rada rs have been postprocessed with a texture-based technique for ground clutte r removal, because, especially for noncoherent radar data, postprocessing b rings a significant improvement. The macroscopic "biases" related to the ra dar detection environment are reduced using a correction technique based on a weighted, multiple regression. The correction technique requires effecti ve clutter suppression. Best results are obtained by weighing the regressio n with the total amount of rain estimated by radar. Within the 40 hour obse rvation period the average precipitation measured by the gages is 160 mm. T he average of uncorrected radar values at gage locations is about 40 mm onl y (for both radars). Thanks to the correction procedure, both the underesti mation and the normalized standard error are reduced by approximately a fac tor of 3 (the normalized standard error is defined as the standard deviatio n between radar and gages divided by the mean radar values at gage location s).