Abstract
Microwave radar is an important tool for observation of birds in flight and represents a tremendous increase in observation capability in terms of amount of surveillance space that can be covered at relatively low cost. Based on off‐the‐shelf radar hardware, automated radar tracking systems have been developed for monitoring avian movements. However, radar used as an observation instrument in biological research has its limitations that are important to be aware of when analyzing recorded radar data. This article describes a method for exploring the detection capabilities of a dedicated short‐range avian radar system used inside the operational Smøla wind‐power plant. The purpose of the testing described was to find the maximum detection range for various sized birds, while controlling for the effects of flight tortuosity, flight orientation relative to the radar and ground clutter. The method was to use a dedicated test target in form of a remotely controlled unmanned aerial vehicle (UAV) with calibrated radar cross section (RCS), which enabled the design of virtually any test flight pattern within the area of interest. The UAV had a detection probability of 0.5 within a range of 2,340 m from the radar. The detection performance obtained by the RCS‐calibrated test target (−11 dBm2, 0.08 m2 RCS) was then extrapolated to find the corresponding performance of differently sized birds. Detection range depends on system sensitivity, the environment within which the radar is placed and the spatial distribution of birds. The avian radar under study enables continuous monitoring of bird activity within a maximum range up to 2 km dependent on the size of the birds in question. While small bird species may be detected up to 0.5–1 km, larger species may be detected up to 1.5–2 km distance from the radar.
Highlights
Birds link ecosystem processes and communities over long distances making them special from the perspective of ecosystem services, including transport of energy, nutrients, propagules, parasites, and pathogens (Bauer & Hoye, 2014; Whelan, Wenny, & Marquis, 2008).The study of flight behavior, migration phenomena, and responses of birds to man-made structures such as wind turbines requires ways to observe and document the movement of birds in the area of interest
These methods have been complemented with individual-based telemetry methods (Bridge et al, 2011)
The modeled species-specific detection ranges signify the minimum limit beyond which the avian radar tracking system is expected to lose track of a given bird
Summary
Birds link ecosystem processes and communities over long distances making them special from the perspective of ecosystem services, including transport of energy, nutrients, propagules, parasites, and pathogens (Bauer & Hoye, 2014; Whelan, Wenny, & Marquis, 2008). In addition to radar-inherent limitations, off-the-shelf automated avian radar track-while-scan systems employ algorithms designed to handle unwanted reflections (clutter) and track birds (i.e., moving targets) over time These tracking algorithms may potentially further affect detection of a bird in—irregular—flight with regard to aspect and tortuosity (Dokter et al, 2013; McCann & Bell, 2017). The aim of this study was to verify the performance of avian radar concerning the detection and tracking of small flying objects, such as birds, within the settings of a wind-power plant. Given the environment it was placed in, we investigated the limitations of the avian radar in successfully detecting moving targets. The groundtruthed birds did not represent a representative subset of the geographic distribution of birds in the area, it does give an indication of the range of possible detections
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