Tracking Migratory Birds: Applying a Passive Tracking Technique Using Direction of Arrival from VHF Radio Tags
As the offshore wind power industry grows along the U.S Atlantic Coast, biologists need to assess potential conflicts between birds and wind turbines. There is a pressing need to develop accurate tracking systems that can evaluate movements of volant (flying) organisms near offshore wind facilities during both the pre-construction and post-construction phase in U.S. waters. Based on research in Europe, turbines at offshore wind facilities can present a collision risk to birds, as well as a migration barrier. Available tracking technology has difficulties tracking fine-scale temporal and spatial movements of small (<200 >g) volant organisms. The functionality of a direction finding (DF) system that uses phase differences to accu- rately obtain bearings from a 3-element omni-directional antenna array was tested. Each antenna was equally spaced (0.889 m) by a distance of a half-wavelength. The open source Software Defined Radio (SDR) software on a PC integrates the FUNCube dongle (FCD) by setting the tuner frequency and sample rate. The FCD demodulates the received signals and converts them to a digital signal after a series of filtering steps. Once converted, the data is saved to a .wav file for post processing using MATLAB. To test the accuracy of this prototype tracking system, a series of drone flights were initiated, with a digitally-coded VHF transmitter attached, to test the viability of this system. However, one receiver failed due to PC memory issues thus the results for estimating bearings were limited to two antennas. For purposes of algorithm testing, estimates were shifted to the correct quadrants (0° − 180° or 180° − 360°) based on apriori information to com- pensate for the ambiguous bearing estimates from using only two antennas. At very short ranges, bearing accuracy suffered due to the directivity of the antennas. The system performed best (±6°) when the transmitter was farther than 175 m from the array, relatively well (±15°) when the transmitter was over 100 m away from the array, and poorly (±50°) when within 100 m of the antenna array. The research did show it was feasible to track azimuth angles through phase measurements. With further developments to the current design, it could be feasible to design an antenna array and continuous receiver to monitor fine-scale movements of VHF-tagged birds using phase measurements.
"Tracking Migratory Birds: Applying a Passive Tracking Technique Using Direction of Arrival from VHF Radio Tags"
Dissertations and Master's Theses (Campus Access).