Answers.Body: <p>I do not know what these sounds are either.  But I would suspect self-noise on the mooring, and would recommend a close look at any plastic parts that could rub against the hydrophone, its cable or against other parts of the mooring close to the hydrophone (e.g., cable tie or elastic suspension bands against the hydrophone capsule, or subsea float shifting against a polypropylene rope).  Can you correlate the incidence of the sounds against sea conditions or current speed perhaps?</p>
  
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Answers.Body: <p>Thank you for your answers! We are investigating the plastic hypothesis (we didn't think about it) even if we don't think it is the case, as our systems are moored with very few plastic + we are using the same system on numerous hydryphones since a long time and we never noticed this type of sounds! + the irregularity and variety of sounds make me think it is not something like that. We have new recordings with similar sounds. We will continue to investigate and I will send more spectro later. We are also investigating if it is related to environmental conditions.</p>
  
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Answers.Text: Hi Marjolaine, thanks for your feedback and let us know your findings. Please consider to move your comment to the comment section below your question or one of the answers ("Add a comment" buttons)
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Answers.Body: <p>I admit that I have no idea what the sound could be, but I would like to offer one or two considerations.</p>
  <p>Any mystery sound begs for special care during analysis.</p>
  <p>Absorption loss at 40 kHz is ~10dB/km, at 100 kHz ~40 dB/km and at 150 kHz ~65 dB/km. So, if you see a sweep from 100 to 40 kHz, the source must be very close.</p>
  <p>Apart from the first figure where nice FM sweeps are visible, other sounds are more pulsed sounds, i.e. high amplitide modulation, or sequences of transients.</p>
  <p>Vertical lines (beginning and end of sound event) are indications that the sound started and ended abruptly, which is typically for mechanically generated sound.</p>
  <p>I first would try to exclude system sound. Plastic is very famous for such high frequency sound, especially when plastic ropes rub on plastic containers. Is there any plastic in the system that can be the culprit? If yes, then I would not get too excited about the mystery sound. If not, then save the save the time and sound snippet, in case this sound repeats in the future.</p>
  <p>Concerning natural sounds, I would check if there are any indication on the presence of, say, seals or cetaceans, before or after these sound events.</p>
  
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Body: <p>In the North of France, we have several recordings full of very high-frequency dolphin-type sounds (like clicks, whistles, calls?, burst pulses. etc...) with almost all frequencies above 40kHz up to 150kHz and the whistles/moan/call types are very short in time. We have consecutive days full of these sounds in December, January, and February, and then the occurrence is decreasing. For now,  these patterns happened in at least 2 recording stations; one at 7 km from the shore, the other one at 35km offshore. Days and night.</p>
  <p>I'm showing you several spectrogram types. Any idea what it could be?</p>
  <p><a href="https://i.sstatic.net/aVhPX.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/aVhPX.jpg" alt="enter image description here" /></a></p>
  <p><a href="https://i.sstatic.net/Y2FFp.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Y2FFp.jpg" alt="enter image description here" /></a></p>
  <p><a href="https://i.sstatic.net/d29dT.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/d29dT.png" alt="enter image description here" /></a></p>
  <p><a href="https://i.sstatic.net/3e0vp.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/3e0vp.png" alt="enter image description here" /></a></p>
  
Tags: <pam><mystery-sound><vocalization><frequency><acoustic-monitoring>
Title: Very high frequency sounds in Northern France
ThreadText: # Very high frequency sounds in Northern France
  
  (Asked by: username_0 on 2023-10-17)
  
  In the North of France, we have several recordings full of very high-frequency dolphin-type sounds (like clicks, whistles, calls?, burst pulses. etc...) with almost all frequencies above 40kHz up to 150kHz and the whistles/moan/call types are very short in time. We have consecutive days full of these sounds in December, January, and February, and then the occurrence is decreasing. For now, these patterns happened in at least 2 recording stations; one at 7 km from the shore, the other one at 35km offshore. Days and night.
  
  I'm showing you several spectrogram types. Any idea what it could be?
  
  [![enter image description here](https://i.sstatic.net/aVhPX.jpg)](https://i.sstatic.net/aVhPX.jpg)
  
  [![enter image description here](https://i.sstatic.net/Y2FFp.jpg)](https://i.sstatic.net/Y2FFp.jpg)
  
  [![enter image description here](https://i.sstatic.net/d29dT.png)](https://i.sstatic.net/d29dT.png)
  
  [![enter image description here](https://i.sstatic.net/3e0vp.png)](https://i.sstatic.net/3e0vp.png)
  
  **Tags:** pam, mystery-sound, vocalization, frequency, acoustic-monitoring
  
  
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  ## 3 answers
  
  ### Answer by username_1 on 2023-10-20. Score: 2
  
  I do not know what these sounds are either. But I would suspect self-noise on the mooring, and would recommend a close look at any plastic parts that could rub against the hydrophone, its cable or against other parts of the mooring close to the hydrophone (e.g., cable tie or elastic suspension bands against the hydrophone capsule, or subsea float shifting against a polypropylene rope). Can you correlate the incidence of the sounds against sea conditions or current speed perhaps?
  
  
  ---
  
  ### Answer by username_0 on 2023-10-27. Score: 1
  
  Thank you for your answers! We are investigating the plastic hypothesis (we didn't think about it) even if we don't think it is the case, as our systems are moored with very few plastic + we are using the same system on numerous hydryphones since a long time and we never noticed this type of sounds! + the irregularity and variety of sounds make me think it is not something like that. We have new recordings with similar sounds. We will continue to investigate and I will send more spectro later. We are also investigating if it is related to environmental conditions.
  
  > **Comments:**
  > **username_2**: Hi Marjolaine, thanks for your feedback and let us know your findings. Please consider to move your comment to the comment section below your question or one of the answers ("Add a comment" buttons)  
  
  ---
  
  ### Answer by username_3 on 2023-10-18. Score: 0
  
  I admit that I have no idea what the sound could be, but I would like to offer one or two considerations.
  
  Any mystery sound begs for special care during analysis.
  
  Absorption loss at 40 kHz is ~10dB/km, at 100 kHz ~40 dB/km and at 150 kHz ~65 dB/km. So, if you see a sweep from 100 to 40 kHz, the source must be very close.
  
  Apart from the first figure where nice FM sweeps are visible, other sounds are more pulsed sounds, i.e. high amplitide modulation, or sequences of transients.
  
  Vertical lines (beginning and end of sound event) are indications that the sound started and ended abruptly, which is typically for mechanically generated sound.
  
  I first would try to exclude system sound. Plastic is very famous for such high frequency sound, especially when plastic ropes rub on plastic containers. Is there any plastic in the system that can be the culprit? If yes, then I would not get too excited about the mystery sound. If not, then save the save the time and sound snippet, in case this sound repeats in the future.
  
  Concerning natural sounds, I would check if there are any indication on the presence of, say, seals or cetaceans, before or after these sound events.
  
  
  ---
  
  