CONTAMINATION OF WIND PROFILER DATA BY MIGRATING BIRDS - CHARACTERISTICS OF CORRUPTED DATA AND POTENTIAL SOLUTIONS

Winds measured with 915- and 404-MHz wind profilers are frequently fou nd to have nonrandom errors as large as 15 m s(-1) when compared to si multaneously measured rawinsonde winds. Detailed studies of these erro rs, which occur only at night below about 4 km in altitude and have a pronounced seasonal pattern, indicate that they are due to the wind pr ofilers' detection of migrating songbirds (passerines). Characteristic s of contaminated data at various stages of data processing are descri bed, including raw time series, individual spectra, averaged spectra, 30- or 60-s moments, 3- or 6-min winds, and hourly averaged winds. An automated technique for the rejection of contaminated data in historic al datasets, based on thresholding high values of moment-level reflect ivity and spectral width, is shown to be effective. Techniques designe d for future wind profiler data acquisition systems are described that show promise for rejecting bird echoes, with the additional capabilit y of being able to retrieve the true wind velocity in many instances. Finally, characteristics of bird migration revealed by wind profilers are described, including statistics of the spring (March-May) 1993 mig ration season determined from the 404-MHz Wind Profiler Demonstration Network (WPDN). During that time, contamination of moment data occurre d on 43% of the nights monitored.