Multi-parameter polarimetric estimators of rainfall rate at X-band

This paper presents recent results on developments of new polarimetric techniques for estimations of rainfall parameters using X-band radar measurements. These techniques were developed for the transportable NOAA radar which has full Doppler, polarimetric and scanning capabilities. Differential phase shift data allow robust corrections for partial attenuation and differential attenuation of radar signals thus overcoming a traditional problems of attenuating frequencies. At the same time additional advantages at X-band are gained by stronger differential phase shift signals in comparisons with longer radar wavelengths. Different radar based techniques for estimating rainfall rate were compared to the data from the high resolution rain gauges. These techniques include the traditional Z-R relation approach, the method based on differential phase shift measurements with the assumed drop shape and the combined reflectivity-differential reflectivity - differential phase method which accounts for the changes in the drop shape parameter (i.e., in the slope of drop oblateness-drop size dependence). Comparing radar and gauge data showed that the combined polarimetric method outperformed the Z-R and differential phase shift only approaches in a large interval of rainfall rates from about 2 mm/hour to more than 50 mm/hour. No severe contamination of differential phase signal by the backscatter phase shift was observed even in heavy rains. Different polarization transmission schemes (i.e., the fast switch between horizontal and vertical polarizations and 45 degree slant linear polarization transmission) are discussed.