The Bio-Acoustic Sonar uses active acoustics to measure populations of zooplankton and fish. The sonar emits sound waves into the water column which bounce off organisms back towards the sensor in a phenomenon known as “backscatter.” The more organisms, the higher the backscatter. The cabled sonar instruments stream data back to shore in near real-time. Sonar signals are calibrated using tungsten spheres of a known size and density, and validated by conducting net tows to capture and count organisms of relevant size in the sonar deployment area.
The cabled sonar instruments (modified Kongsberg Simrad EK60 Echo Sounder; OOI series ZPLSC-B) sense active acoustic pressure waves at 38 kHz and 200 kHz on single channel transducers, and on a 120 kHz split beam transducer.