A digital Hydrophone is a passive acoustic sensor (an underwater microphone) that converts sound energy to electrical energy, with a binary stream output. The Broadband Acoustic Receiver (Hydrophone) listens for seismic events, landslides, sea creatures, and human-generated noise in the ocean, and can hear and record everything from marine mammals in the water column to rain at the surface. The OOI requirements specified very broadband hydrophones with good noise floor characteristics and a wide dynamic range. The waters offshore of Oregon are “alive” with the calls of marine mammals, each of which have distinctive vocalizations. By processing the different frequencies, individual mammals can be identified including blue, gray, and fin whales that vocalize at different intervals and pitches.
There are six Ocean Sonics icListen HF broadband hydrophones on the Cabled Array. At the Oregon Shelf and Offshore sites they are cabled to the Benthic Experiment Packages (BEPs), and at the Oregon Slope Base and Axial Base sites they are connected to the Low-Power Junction Boxes. Two others are located on the Platform Interface Assemblies at 200 m water depth on the Shallow Profiler Moorings at Slope Base and at Axial Base.