Drop shape and DSD retrieval with an X-band dual polarization radar

Several drop size distribution and drop shape retrieval methodologies were proposed and evaluated mainly at S-band where attenuation effects are usually negligible. However, recent improvements in attenuation correction allow to extend such retrieval techniques at attenuating frequencies, such as X-band. Most up to date attenuation correction methodologies are based on a constraint so that the path attenuation is distributed over each range bin contained in the path. These techniques have been improved exploiting the inner self-consistency of radar measurements. This self consistent methodology provides an optimization procedure to obtain the best estimate of attenuation and differential attenuation. The main goal of this study is the examination of the drop shape and drop size distribution retrieval from X-band radar measurements after attenuation correction.

Interpretation of polarimetric radar measurements in rainfall such as differential reflectivity and specific differential phase shifts depends on the mean raindrop shape–size relationship. Following the results obtained on the drop shape variability by Gorgucci et al. (JAS, 2006), a more robust algorithm to obtain the mean raindrop shape from polarimetric radar measurements is used. Once the mean drop shape is determined, it is possible to retrieve DSD parameters from radar measurements. The procedures are evaluated using both X-band profiles simulated from measured S-band profiles and radar measurements collected in 2001 by the NOAA X-band polarimetric radar during the field campaign at the NASA Wallops Island facility in Virginia.