The basis of acoustic zooplankton sampling is that sound waves are emitted into the water and objects which have a different density than the surrounding water will tend to reflect sound. A transducer, such as this strut-mounted one resting on the deck, will emit a sound pulse about once a second into the water. When this pulse of sound hits an object, a fraction of the reflected sound is received back by the transducer. This reflected or echoed sound energy is then passed to the echosounder. The echo energy is received by our scientific echosounder .
Sound intensity is recorded by varying scales of black intensity marks on the chart paper.
Output from the echosounder is also recorded digitally by a computer. We run our echosounder while steaming along transect lines during the daylight hours. This echosounder will record intensities of fish and zooplankton in the water below the ship to a depth of 250 m. Acoustic records will be later processed to determine actual biomass estimates . This is part of a chart for our zooplankton acoustic lines in the Strait of Georgia. Black lines indicate our standardized transects.