Development and Evaluation of an Ultrasonic Transmitter Using Frequency–Modulated Tones for Biotelemetry

Abstract

Biotelemetry is widely used to identify the position of aquatic animals. In order to observe micro scale movements of small target species, positioning accuracy is yet to be improved. It is known that frequency modulated signals provides better positioning accuracy. However, the conventional biotelemetry studies have used single-frequency transmitters. The purpose of this study is to develop a new type of ultrasonic transmitter using frequency-modulated tones (FM pinger) to reduce the positioning errors of biotelemetry. We conducted experiments to compare the accuracy of time difference of arrival (TDOA) by using the FM signals and conventional single-frequency signals in an open sea. We tested six patterns of frequency modulation including single-frequency (0, 2, 4, 6, 8, 10 kHz) with two kinds of duration (2, 10 msec.) for each frequency modulation bandwidth. The results showed that the TDOA of frequency-modulated tones provided higher accuracy than single-frequency tones. The average and standard deviation of TDOA of the frequency-modulated tones were close to the theoretical value of TDOA and 0. Therefore, it was considered that the frequency-modulated tones enhance accurate positioning as compared to the single-frequency tones.