Development of a four-channel underwater passive acoustic monitoring system for the use of underwater vehicles

The purpose of this research is to develop a four-channel underwater passive acoustic monitoring system for the use of underwater vehicles. Humans have received abundant blessings of the ocean, and thus it is very important to recognise marine biodiversity and to maintain sound ocean ecosystems for the sustainable utilisation of the ecosystem services. Final goal of this research is to realise a long-term and wide-range monitoring of marine mammals using autonomous underwater vehicles, and to evaluate the healthiness of ocean ecosystems and environments. Underwater glider has no propulsive machinery, and then it is one of the most suitable underwater vehicles for acoustic observation. It is widely known that killer whale is the top predator of ocean food chain. Recently, passive acoustic monitoring (PAM) of marine mammals has appeared in the spotlight. This paper deals with a 4-channel underwater passive acoustic monitoring system. Maximum operational depth is 400 metre. The system consists of four hydrophones, pre-amplifier with anti-aliasing low-pass filter, a 4-ch portable recorder. It is also equipped with a 3-axis digital compass, a GPS device, and a 2-ch serial data logger so as to estimate the accurate direction of sound source even though the system may be drifted in the waves.