Inexpensive passive acoustic animal tracking system

Marine bioacoustic research is challenged by economic, logistical, and technical barriers. A multibuoy recording system has been designed. Each buoy contains a DAT recorder (SONY D-8; 9 Hz–22 kHz) with a hydrophone (Hi-Tech HTI-SSQ-41B; 10 Hz–30 kHz) connected to one channel for collecting passive acoustic data. The second channel records time-synchronizing VHF radio signals, for computing time-of-arrival differences between buoys. A GPS data logger documents buoy position. This package is encased in a PVC spar-buoy housing. During analysis, cross correlation and peak picking time synchronize the separate recordings. Cross-correlation or waveform measurement is used to determine time-of-arrival differences of vocalizations between buoys. A hyperbolic least-squares fixing algorithm is used to calculate locations of vocalizing animals. In a calibration test, three buoys were deployed in triangle formation (1.8-km spacing). Light bulb implosions were localized with an accuracy of 0.20 km. The buoys are far less expensive (approximately $1900 each) than systems requiring towed arrays, multichannel signal conditioning/recording, and large tow ships, or fixed bottom-mounted arrays. Buoys are deployable wherever animals are located, in sea state conditions through Beaufort 5. These buoys have recorded eight marine mammal species. [Work supported by ONR, ATOC, AMNH, Friends of LML, and Myers trust fund.]