Many marine animals rely on sound to navigate, communicate, and feed. Cetaceans (whales, dolphins, and porpoises) are especially sensitive to sound in the ocean. Because ADCPs are acoustic instruments, some agencies will require proof that they will not negatively affect these animals while they are deployed and transmitting sound pulses into the water column.
Nortek ADCPs operate over a range of frequencies from 55 kHz to 2 MHz. Once the sound pulse has been emitted, the intensity is greatly reduced within a few meters due to scattering and absorption. Studies have shown no significant behavioural response of marine mammals to ADCPs deployed underwater (Coakley, 2011) - while the lower-frequency instruments may be audible to some marine animals (see attached document "Estimated Auditory Bandwidths for Marine Mammals and Fish"), communications will not be masked due to the short pulse lengths, short duty cycles, and low power output of the instruments, and hearing impairment or other ill-effects are not expected due to the low power output.
Please contact Nortek Support if you require full environmental impact details for your instrument.