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Bird strikes are the most common wildlife hazard to aviation safety (Dolbeer et al. 2000). Advances in habitat management at airports through the elimination and reduction of attractants, in combination with hazing and lethal control, have reduced avian hazards 120 km, this approach can be used to delimit locations of postbreeding and nocturnal roost sites of birds such as purple martins (Progne subis; Fig. 13.2), as well as to quantify the density of birds (Russell and Gauthreaux 1998) and bats (Horn and Kunz 2008). The greatest limitation of the WSR-88D for use in biological studies has been the size of the radar’s legacy pulse volumes (1° × 1 km), which increases with increasing distance. This corresponding growth prohibits gathering information on small, individual targets and combines the return from several different types of targets into one pulse volume. The upgrade to superresolution should improve this shortcoming, but resolution cells (0.5° × 250 m) will still be sampling a large volume of atmosphere. Because the lowest antenna scan is at an angle of 0.5° above the horizontal, it is commonplace for low-flying targets to go undetected because they are below radar coverage. Terminal Doppler Weather Radar Although terminal Doppler weather radar (TDWR) has not been assessed adequately for its ability to detect migrating birds, its operational characteristics suggest it should be an excellent sensor for that purpose (Istok et al. 2008). TDWR was developed for the Federal Aviation Administration in the early 1990s to detect real-time wind shear and high-resolution precipitation data, and as of 2009, 45 units were deployed near major airports across the USA (Fig. 13.3). The radar operates at the C band or 5-cm wavelength (5,600–5,650 MHz) and has a peak power of 250 kW. Antenna beam Fig. 13.2. Display of the WSR-88D radar at Cincinnati, Ohio, USA, at 1039 GMT on 2 August 2010. The circles show Purple Martins (Progne subis) departing from overnight roosts. The strobe is from the rising sun, which emits microwaves similar to those emitted by the radar. The density of birds can be estimated from the reflectivity scale (in decibels relative to Z, or dBZ) on the right. Fig. 13.3. Locations and station codes of the 45 terminal Doppler weather radar units in the USA. The units are located near airports to monitor wind shear and severe weather. 144 wildlife monitoring width is 0.55°, and the antenna completes twenty-three 360° sweeps every 6 min in severe/hazardous mode. Reflectivity of targets can be measured to 460 km distant while Doppler (radial) velocity of targets can be measured to 89 km (55 miles). Although similar in operation to the WSR-88D, the resolution of TDWR is greater, and TDWR antennae can scan below an angle of 0.5° above the horizontal, providing information on bird activity at the scale of an airfield. High-Resolution Marine Surveillance Radars Casement (1966) was one of the first to use marine surveillance radar on a ship to study bird migration, and interest in using marine radar to study bird movements subsequently increased (Williams et al. 1972, Williams 1984). Because of the relatively low cost of marine surveillance radar, this technology has been used extensively for bird detection at airports (e.g., MacKinnon 2006) and for environmental impact studies (e.g., National Academy of Sciences 2007). Technical Specifications The following radar characteristics are known to in- fluence the results obtained from radar studies of bird movements: • Transmitter power (e.g., 5, 10, 25, 50, or 60 kW) • Frequency or wavelength • Pulse length and corresponding pulse repetition frequencies • Antenna beam characteristics • Antenna rotation speed • Tuning of the receiver • Magnetron or solid state • Gain setting • Range setting • Ground and sea- and rain-clutter settings • Beam-brilliance setting Most of the small, mobile radars used to monitor bird movements have been low-powered (5–60 kW) marine-surveillance radars of 3- or 10-cm wavelengths and are commonly referred to as “avian radars.” The transmitter power of the avian radar should be as high as possible (≥25 kW) to maximize resolution and sensitivity . Long pulse lengths enhance detectability but have lower resolution, whereas short pulse lengths increase resolution with decreased detectability. The greater the transmitter power, the greater the cost, but a 50-kW radar operating on short pulse will produce superior results for bird detection than a 10-kW unit operating on short pulse. Marine radars can be purchased in...

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