Estimation of Attenuation at X-band Using Propagation Phase and Differential Reflectivity

An attenuation estimation method that uses both differential reflectivity (ZDR) and propagation phase (ΦDP) concurrently is described. The attenuation method is based on variational algorithm. The majority of the attenuation estimation methods use ΦDP only. A detailed observing system simulation experiment (OSSE) was used to evaluate performance of the variational-based method and ΦDP-based methods for attenuation estimation. The variational-based method always estimated more accurate attenuation than ΦDP-based method. Practical utility of the variational-based method attenuation correction was demonstrated using radar field measurements from TEAM-R (Taiwan Experimental Atmospheric Mobile - Radar) during SoWMEX/TiMREX 2008. Accuracy of attenuation corrected X-band measurements in actual field measurements were evaluated by comparing them with collocated NCAR S-band radar measurements. It was shown that the variational-based method is relatively less sensitive to measurement noise in radar observations. There were instances where large artifacts in ZDR and ΦDP due to steep gradients in storm intensity limited usefulness of the variational-based method, ΦDP-based method is used as an alternate. Variational corrected ZHH and ZDR from attenuation corrected X-band radar measurements is also compared with disdrometer observations.