Answers.Body: <p>Additional to Mark's answer mentioning the sound speed profile and SOFAR channel, there are effects in shallow water that increase transmission loss, especially for lower frequencies:</p>
  <p>In shallow water sediment interaction of the sound will often be the dominant source of sound attenuation (for anything but very hard sediments) (see: <a href="https://dosits.org/science/advanced-topics/shallow-water-propagation/" rel="noreferrer">https://dosits.org/science/advanced-topics/shallow-water-propagation/</a> &amp; <a href="https://dosits.org/science/advanced-topics/how-does-sound-travel-in-very-shallow-waters/" rel="noreferrer">https://dosits.org/science/advanced-topics/how-does-sound-travel-in-very-shallow-waters/</a>).</p>
  <p>This attenuation is frequency dependent, but generally the seafloor acts like a highpass filter, causing low frequencies (which dominate ship noise and long range noise) to be absorbed (see: <a href="https://www.researchgate.net/publication/343987334_Accounting_for_sea_floor_properties_in_the_assessment_of_underwater_noise_radiated_from_ships_in_shallow_water" rel="noreferrer">https://www.researchgate.net/publication/343987334_Accounting_for_sea_floor_properties_in_the_assessment_of_underwater_noise_radiated_from_ships_in_shallow_water</a> for good introduction and model).</p>
  <p>In general frequencies ~&lt; 200 Hz are absorbed and dissipated in shallow water, and higher frequencies attenuate due to volume scattering and heat loss leaving the dominant noise in shallower waters between several hundred Hz and a few kHz.</p>
  <p>In deeper waters, with no mechanism for low frequency attenuation, low frequency noise can travel very far (even in the absence of a SOFAR channel) given the negligible attenuation loss (see: <a href="http://resource.npl.co.uk/acoustics/techguides/seaabsorption/" rel="noreferrer">http://resource.npl.co.uk/acoustics/techguides/seaabsorption/</a>).</p>
  
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Answers.UserDisplayName: Rasmus
Answers.Body: <p>What you're seeing there is an effect of the ocean <a href="https://en.wikipedia.org/wiki/Thermocline" rel="noreferrer">thermocline</a>.  The speed of sound changes rapidly in the upper few hundred meters of the ocean from a combination of temperature and pressure changes (sound moves faster in warmer water, and in higher-pressure water).  This produces a natural <a href="https://en.wikipedia.org/wiki/Waveguide" rel="noreferrer">waveguide</a> called the <a href="https://en.wikipedia.org/wiki/SOFAR_channel" rel="noreferrer">SOFAR channel</a>, which can carry sounds for thousands of kilometers.</p>
  <p>It's suspected that <a href="https://archive.ph/20120826003933/http://www3.interscience.wiley.com/journal/119693602/abstract" rel="noreferrer">fin whales use this channel for communication</a>.</p>
  
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Answers.UserDisplayName: Mark
Body: <p>I saw the following graph in a blog post about how shipping noise affects whales. Why does the sound seem to propagate better in deep water than in shallow water? Are there any known marine species that changed their preferred depth due to this effect?</p>
  <p><a href="https://i.sstatic.net/8f7JG.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/8f7JG.jpg" alt="Sound propagation" /></a>
  <a href="https://www.frontiersin.org/articles/10.3389/fmars.2019.00606/full" rel="nofollow noreferrer">© 2019 Erbe, Marley, Schoeman, Smith, Trigg and Embling</a></p>
  
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Comments.Text: If one of the answers below answers your question, please 'accept' the answer by checking the checkmark under the vote tally. See https://stackoverflow.com/help/someone-answers
Comments.UserDisplayName: Shannon
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Comments.Text: Could you add a link/credit to the figure? Remember that all content on SE is under the license Creative Common.
Comments.UserDisplayName: Noil
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Comments.Text: @Noil based on reverse image search, I think the original source is https://www.frontiersin.org/articles/10.3389/fmars.2019.00606/full
Comments.UserDisplayName: 416E64726577
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Comments.Text: I've just added it below the image
Comments.UserDisplayName: Noil
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Comments.CreationDate: 2022-06-26T08:47:33.730Z
Comments.Text: Could you please add information on model used (bellhop?) and on frequency?
Comments.UserDisplayName: WMXZ
Tags: <marine-species><sound-propagation><water>
Title: Why does sound from ships propagate better in deep water than in shallow water?
ThreadText: # Why does sound from ships propagate better in deep water than in shallow water?
  
  (Asked by: username_0 on 2022-06-22)
  
  I saw the following graph in a blog post about how shipping noise affects whales. Why does the sound seem to propagate better in deep water than in shallow water? Are there any known marine species that changed their preferred depth due to this effect?
  
  [![Sound propagation](https://i.sstatic.net/8f7JG.jpg)](https://i.sstatic.net/8f7JG.jpg)
  [© 2019 Erbe, Marley, Schoeman, Smith, Trigg and Embling](https://www.frontiersin.org/articles/10.3389/fmars.2019.00606/full)
  
  **Tags:** marine-species, sound-propagation, water
  
  > **Comments:**
  > **username_3**: Could you please add information on model used (bellhop?) and on frequency?  
  > **username_1**: If one of the answers below answers your question, please 'accept' the answer by checking the checkmark under the vote tally. See https://stackoverflow.com/help/someone-answers  
  > **username_2**: Could you add a link/credit to the figure? Remember that all content on SE is under the license Creative Common.  
  > **username_0**: @username_2 based on reverse image search, I think the original source is https://www.frontiersin.org/articles/10.3389/fmars.2019.00606/full  
  > **username_2**: I've just added it below the image  
  
  ---
  
  ## 2 answers
  
  ### Answer by username_5 on 2022-06-23. Score: 10 | Accepted answer
  
  What you're seeing there is an effect of the ocean [thermocline](https://en.wikipedia.org/wiki/Thermocline). The speed of sound changes rapidly in the upper few hundred meters of the ocean from a combination of temperature and pressure changes (sound moves faster in warmer water, and in higher-pressure water). This produces a natural [waveguide](https://en.wikipedia.org/wiki/Waveguide) called the [SOFAR channel](https://en.wikipedia.org/wiki/SOFAR_channel), which can carry sounds for thousands of kilometers.
  
  It's suspected that [fin whales use this channel for communication](https://archive.ph/20120826003933/http://www3.interscience.wiley.com/journal/119693602/abstract).
  
  
  ---
  
  ### Answer by username_4 on 2022-06-23. Score: 9
  
  Additional to username_5's answer mentioning the sound speed profile and SOFAR channel, there are effects in shallow water that increase transmission loss, especially for lower frequencies:
  
  In shallow water sediment interaction of the sound will often be the dominant source of sound attenuation (for anything but very hard sediments) (see: <https://dosits.org/science/advanced-topics/shallow-water-propagation/> & <https://dosits.org/science/advanced-topics/how-does-sound-travel-in-very-shallow-waters/>).
  
  This attenuation is frequency dependent, but generally the seafloor acts like a highpass filter, causing low frequencies (which dominate ship noise and long range noise) to be absorbed (see: <https://www.researchgate.net/publication/343987334_Accounting_for_sea_floor_properties_in_the_assessment_of_underwater_noise_radiated_from_ships_in_shallow_water> for good introduction and model).
  
  In general frequencies ~< 200 Hz are absorbed and dissipated in shallow water, and higher frequencies attenuate due to volume scattering and heat loss leaving the dominant noise in shallower waters between several hundred Hz and a few kHz.
  
  In deeper waters, with no mechanism for low frequency attenuation, low frequency noise can travel very far (even in the absence of a SOFAR channel) given the negligible attenuation loss (see: <http://resource.npl.co.uk/acoustics/techguides/seaabsorption/>).
  
  
  ---
  
  