Hindawi Publishing Corporation Advances in Meteorology Volume 2013, Article ID 769275, 13 pages http://dx.doi.org/10.1155/2013/769275 Research Article Using WSR-88D Polarimetric Data to Identify Bird-Contaminated Doppler Velocities Yuan Jiang, 1,2,3 Qin Xu, 4 Pengfei Zhang, 3,4 Kang Nai, 3 and Liping Liu 1 1 State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081, China 2 Nanjing University of Information Science and Technology, Jiangsu Province 210044, China 3 Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma, Norman, OK 73072, USA 4 National Severe Storms Laboratory, David L. Boren Boulevard, Norman, OK 73072, USA Correspondence should be addressed to Qin Xu; qin.xu@noaa.gov Received 6 May 2013; Revised 21 May 2013; Accepted 21 May 2013 Academic Editor: Jidong Gao Copyright © 2013 Yuan Jiang et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. As an important part of Doppler velocity data quality control for radar data assimilation and other quantitative applications, an automated technique is developed to identify and remove contaminated velocities by birds, especially migrating birds. his technique builds upon the existing hydrometeor classiication algorithm (HCA) for dual-polarimetric WSR-88D radars developed at the National Severe Storms Laboratory, and it performs two steps. In the irst step, the fuzzy-logic method in the HCA is simpliied and used to identify biological echoes (mainly from birds and insects). In the second step, another simple fuzzy logic method is developed to detect bird echoes among the biological echoes identiied in the irst step and thus remove bird-contaminated velocities. he membership functions used by the fuzzy logic method in the second step are extracted from normalized histograms of diferential relectivity and diferential phase for birds and insects, respectively, while the normalized histograms are constructed by polarimetric data collected during the 2012 fall migrating season and sorted for bird and insects, respectively. he performance and efectiveness of the technique are demonstrated by real-data examples. 1. Introduction Radar echoes from migrating birds can severely contaminate Doppler velocity measurements (Jungbluth et al. [1]; Gau- threaux et al. [2]). For meteorological applications, especially quantitative applications in radar data assimilation, it is necessary to remove bird-contaminated velocities using an automated identiication technique. Such a technique was developed previously before the operational WSR-88D radars in the US were upgraded with dual-polarization capability (Zhang et al. [3]; Liu et al. [4]), but the technique could only crudely detect and remove bird-contaminated veloci- ties volume-wise or tiltwise (for each sweep) because the usable input data from operational WSR-88D radars were limited to relectivity and velocity measurements. A major drawback of this previous technique is that it rejects the entire volume (or tilt) of velocity observations even if only a fraction of the volume (or tilt) is contaminated by migrating birds. Now, almost all the operational WSR-88D radars in the US are upgraded with dual-polarization capability, which is essential for discriminating between meteorologi- cal and nonmeteorological scatterers and for distinguishing diferent hydrometeor types. In the hydrometeor classiica- tion algorithm (HCA) developed for polarimetric radars at the National Severe Storms Laboratory (NSSL) (Straka and Zrni´ c[5]; Zrni´ c and Ryzhkov [6]; Zrni´ c et al. [7]; Schuur et al. [8]; Ryzhkov et al. [9]; Park et al. [10]), birds and insects are not distinguished and labeled as biological scatterers entirely. his HCA is designed to remove biological scatterer contamination from meteorological scatterers for the pur- pose of quantitative precipitation estimation (QPE). It is thus timely and desirable to develop an improved technique that