Acoustic Moorings

The wet end of the observatory consists of three identical autonomous moored acoustic stations anchored at fixed locations, that pick up and identify the acoustic clicks produced by mammals and transmit the intermediate results in real-time to a land station for further processing and localization. The backbone of each mooring is a stainless steel frame floating vertically on the sea surface and anchored to the seabed with two lines of cable. The mooring has a low center of gravity and is mostly submerged for stability reasons. The section above surface contains a sealed waterproof box that houses a fully autonomous acoustic station for data acquisition, preprocessing and transmission. Acoustic input is provided through a a high-sensitivity low-noise hydrophone located 100 m. below sea level

The station is built around a raspberry Pi 2 microcomputer equipped with a 32 GB SD memory card , a 500 GB solid state disk for data storage, a GPS geolocation module, a GPRS communication module and a multi channel DAQ card that registers and digitizes the received signals. A high sensitivity hydrophone is deployed 100 m. below surface in a special canister that also contains a pressure / temperature sensor. The station is powered through a photovoltaic system that consists of a solar panel mounted on the very top of the mooring, a sealed lead acid battery mounted on the bottom of the mooring (about 2 m. below sea level) for stability reasons and a power regulator inside the system box.

Instrument canister and connecting cable

A custom made waterproof cylindrical canister is deployed 100 m. below surface and connected to the system through an 8 core shielded cable using waterproof SubConn pluggable electrical connectors. Both the cable and the connectors are provided by MacArtney Underwater Technology. The canister -which is made from Ertacetal and can sustain water pressure at depths of up to 200 m.- houses a high-sensitivity low-noise hydrophone (Benthowave Instruments Inc. model BII-7121) along with a depth and temperature sensor (STS ATM.1ST/T - High Precision Transmitter). This modular design has been selected to allow easy replacement of parts.

System Electronics

The core of the system is built around a Raspberry Pi 2 single board computer connected to a high sampling rate data acquisition unit. The system is also equipped with a GPS/PPS unit for positioning and synchronization and a GPRS unit for two-way communication with the land based station. A solar charge controller unit regulates the energy supply, storage and consumption of the system.