Hello,

I am very much interested to how frequency of sound varies in water. Also, how the frequency varies with temperature and depth? What are the different formulas related to this? Secondly, how can we determine the best frequency of operation? I would be very thankful if anyone could answer the above questions or point to materials explaining the above.

With regards

Welcome.

Sound underwater is affected by different speed propagation, frequency response, attenuation, depending on temperature, depth pressure, salinity, suspended solids...

Tables are available on the web. The "best frequency" depends on what do you want to do, and bear trade-offs, as everything.

 

Read something about side scan sonar and will learn how different frequencies yield different results, to pick your preferences.

 

----> https://en.wikipedia.org/wiki/Side-scan_sonar

I wish to transmit sensor data. Expected data rate is around few tens of Kbps.

Here you go

 

The bible

 

http://www.amazon.co.uk/Underwater-Acoustic-Positioning-Systems-Milne/dp/0419121005/ref=sr_1_1?s=books&ie=UTF8&qid=1455642872&sr=1-1&keywords=underwater+positioning+systems

 

and a useful e-paperback

 

http://www.amazon.co.uk/Acoustic-Network-Underwater-Positioning-System-ebook/dp/B007QF5IZO/ref=sr_1_2?s=books&ie=UTF8&qid=1455642872&sr=1-2&keywords=underwater+positioning+systems

Any ultrasonic carrier frequency above twice the data rate should suffice, at a power that reaches destination range.

 

----> https://en.wikipedia.org/wiki/Nyquist_rate

 

Will this tickle ¿? ----> http://www.sonardyne.com/products/all-products/instruments/1146-ucomm-underwater-acoustic-modem.html

 

----> http://www.edgetech.com/images/ut-news/EdgeTech-Sea-Technology-mag-article-on-freq-selection.pdf

 

For short ranges, clear waters I would venture/evaluate optical links instead of acoustical.

"how frequency of sound varies in water" is a bit unclear. For instance, the frequency of a sound created in the air keeps the same if it passes to water.

 

The frequency produced by some generators may vary if they're immersed due to the mechanical load by the water's mass.

 

The best frequencies to use in water differ from the atmosphere. For long range, lower frequencies are better, but the gradient of temperature and salinity along the depth create odd effects, with a layer around -800m that guides the sound.