discussion / Acoustics  / 16 November 2023

Hydromoth for coastal & offshore surveying

Hi all! I'm interested in deploying a Hydromoth on an Uncrewed Surface Vehicle (USV) to collect acoustic data for biodiversity analysis, for coastal and offshore marine surveys. We're especially interested in surveying around seagrass beds.

1. Has anyone tried this on a moving vehicle, and had to filter out the noise of motors? The vehicle is electric, but will be producing sound nonetheless.

2. How are the databases for marine wildlife vocalisations in the UK currently?

I'm very interested in adding this to the sensors we plan to deploy so if you have any info, I'm all ears!



Hi Sol,

I think your concern is well placed.  The pros typically tow an array of hydrophones, in its simpler configuration it looks like a long fat rubber hose containing maybe a dozen transducers feeding their electrical signals to a recording unit back on the ship.  All this is done to reduce noise from the ship, from waves crashing, and flow noise.  The multiple transducers can also be electronically tuned to be directional so that it can be "pointed" away from a noise source (like the ship).

In your position, I would just try the simplest thing that could work, then fix the problems as they arise.  It could be you may need to be dead in the water while recording.  To address surface noise (slapping waves, wind), you could mount the hydromoth low down on a spar buoy, which you tow into position.


Best of luck, it sounds like an interesting project (c:

Hydromoths are great for the price but they do not have the most streamlined housing and audio quality won't be as good as something like a SoundTrap or really any recorder with a proper hydrophone and 16-bit +DAQ system.

If you can afford it, this is an excellent SoundTrap based towed autonomous system NOAA have been using. It might work towed behind an autonomous vehicle

Alternatively, if you can have something inside the vehicle, a simple tape recorder (e.g. Tascam DR40X) and hydrophone on cable  will provide excellent sound quality. You could also use something like a Raspberry Pi with audio focussed ADC hat to record but that would require a bit more programming. Even consider a standard AudioMoth and plug a proper hydrophone into the audio jack - this would still have a 12-bit ADC but would provide better sound quality than a hydromoth (hydrophones are more omnidirectional and there's no air filled causing reflections and attenuation)