# Would ultrasound be a valid method of mapping ocean floors given the perceived "gel" is ocean water?

I am a scuba diver, with a big idea that would require me to map various dive sites as I went to them and dove in them. The typical size and other implications of sonar technology would essentially render this impossible.

So I thought, would it be possible to use ultrasound instead? This would theoretically require a device that could, instead of seeing through the warm gel that hospitals use, see through cold ocean water. I've done some research but have not gotten a definitive answer, which is understandable since no one has asked the question.

And, secondly, if ultrasound is not possible, what else is typically (or not typically) used in oceanography besides sonar?

Thanks!

• en.wikipedia.org/wiki/Sonar#Hand-held_sonar_for_use_by_a_diver Feb 23, 2021 at 22:47
• Gel is not necessary, water is fine . The gel is used because it is more convenient than a steady stream of water. Millions of miles of pipe and RR rails have been inspected with UT using water couplent retained in an elastomeric tire. Feb 24, 2021 at 0:52
• And seismic transmission in seawater has been used for offshore petroleum exploration for many decades. Feb 24, 2021 at 0:59
• There isn't really a fundamental difference between Ultrasound as used in medical contexts and Sonar. The choice of frequency for a sonar application is a compromise between range and resolution - medical ultrasound uses high frequencies to resolve fine detail at short range. Sonar tend to use longer frequencies, trading off resolution for range. Feb 25, 2021 at 14:41

It seems that attenuation is much greater at ultrasound frequencies:

50 khz   12-15 dB/km
0.5khz   0.024 dB/km


It depends on what distance and resolution you need.

• Afaik scuba divers only rarely go deeper than 40m, it is life-threatening due to caisson disease. Using helium-oxigen bottles helps some tens meters, but it is not cheap. And they are interested mostly on the seabed below them. So I believe, the 50kHz could work. Feb 23, 2021 at 19:31
• en.wikipedia.org/wiki/Sonar#Frequencies_and_resolutions Feb 23, 2021 at 21:48
• Reading the numbers you state, one could infer the audible ping to trace a submarine displayed in the movies would be much more suitable than ultrasound. But reading about hydrography here states echo sounding routinely deploys 200 kHz for depths up to 100 m, and deep water sounding 33 or 24 kHz. Feb 25, 2021 at 16:34

Optical LIDAR systems for marine use are being developed and are being used for accurate mapping of archaeological remains under water. See https://optics.org/news/8/3/26. However if a sonar is too big and impractical, I imagine oceanographic LIDAR is similarly out of scope.

• Interesting tech, but yeah. I appreciate the info! Mar 1, 2021 at 14:53