[MARMAM] New Paper on "200 kHz" sonar with side lobes audible to marine mammals

Brandon Southall brandon.southall at sea-inc.net
Wed Apr 16 01:54:36 PDT 2014


On behalf of my co-authors, I would like to let you know about a new 
paper on the audibility of high frequency sonar systems to some marine 
mammals. We investigated the acoustic "leakage" of energy into side 
lobes from the 200 kHz center frequency of three commercially-available 
sonar systems. These active sonar systems were being used in efforts to 
detect and track marine mammals around a tidal power turbine site and 
they were not expected to be audible to the animals based on their very 
high frequency. However, behavioral observations of killer whales 
suggested they were in fact detecting them. Our acoustic analysis of the 
systems indicates that there is sufficient downward spread of energy in 
the side bands to expect that these odontocete cetaceans could in fact 
hear them. We conclude that received levels at animals would very likely 
be well below those that could be harmful, but that they could be 
audible and potentially affect behavior over ranges of hundreds of 
meters. A reference to the paper, weblink to the Open Access manuscript, 
and the article abstract are given below. The lead author was PNNL 
engineer Zhiqun (Daniel) Deng and both he and I would appreciate any 
comments or questions on the paper.

Thank you,
Brandon Southall

Deng ZD, Southall BL, Carlson TJ, Xu J, Martinez JJ, et al. (2014) 200 
kHz Commercial Sonar Systems Generate Lower Frequency Side Lobes Audible 
to Some Marine Mammals. PLoS ONE 9(4): e95315. 


The spectral properties of pulses transmitted by three commercially 
available 200 kHz echo sounders were measured to assess the possibility 
that marine mammals might hear sound energy below the center (carrier) 
frequency that may be generated by transmitting short rectangular 
pulses. All three sounders were found to generate sound at frequencies 
below the center frequency and within the hearing range of some marine 
mammals, e.g. killer whales, false killer whales, beluga whales, 
Atlantic bottlenose dolphins, harbor porpoises, and others. The 
frequencies of these sub-harmonic sounds ranged from 90 to 130 kHz. 
These sounds were likely detectable by the animals over distances up to 
several hundred meters but were well below potentially harmful levels. 
The sounds generated by the sounders could potentially affect the 
behavior of marine mammals within fairly close proximity to the sources 
and therefore the exclusion of echo sounders from environmental impact 
analysis based solely on the center frequency output in relation to the 
range of marine mammal hearing should be reconsidered.

Brandon L. Southall, Ph.D.
President, Senior Scientist, SEA, Inc.
Research Associate, University of California, Santa Cruz
9099 Soquel Drive, Suite 8, Aptos, CA 95003, USA
831.332.8744 (mobile); 831.661.5177 (office); 831.661.5178 (fax)
Brandon.Southall at sea-inc.net; www.sea-inc.net

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