200 khz commercial sonar systems generate lower frequency side lobes audible to some marine mammals. Deng, undefined; Z. Daniel AND Southall, undefined; Brandon L. AND Carlson, undefined; Thomas J. AND Xu, undefined; Jinshan AND Martinez, undefined; Jayson J. AND Weiland, undefined; and Mark A. AND Ingraham, undefined PLoS ONE, 9:e95315, Public Library of Science, 2014.
200 khz commercial sonar systems generate lower frequency side lobes audible to some marine mammals [link]Paper  doi  abstract   bibtex   

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.

@ARTICLE{10.1371/journal.pone.0095315,
  author = {Deng, , Z. Daniel AND Southall, , Brandon L. AND Carlson, , Thomas
	J. AND Xu, , Jinshan AND Martinez, , Jayson J. AND Weiland, , Mark
	A. AND Ingraham, , John M.},
  title = {200 khz commercial sonar systems generate lower frequency side lobes
	audible to some marine mammals},
  journal = {PLoS ONE},
  year = {2014},
  volume = {9},
  pages = {e95315},
  abstract = {<p>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.</p>},
  doi = {10.1371/journal.pone.0095315},
  owner = {Tiago Marques},
  publisher = {Public Library of Science},
  timestamp = {2014.04.16},
  url = {http://dx.doi.org/10.1371%2Fjournal.pone.0095315}
}
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