# Hydroacoustics (Doppler)

1. Jan 22, 2014

### JoaoCorvina

Hello!
I'm was wondering if there is anyone that could help a Marine Biologist finding a "simple" way to calculate the sound amplitude degradation with the increasing distance. For example a source produces a sound of 237 dB re 1μPa at 1m (x) and the speed of sound in the water is 1500m/s (y) at what distance is lower than 170 dB re 1μPa at 1m. Considering the sound propagation as in a plane, not in 3 dimensions and the only input I need is the source (in this example was 237 db re 1μPa at 1m) and the speed of water.

If someone could help with this would be great! Would love to understand this matter a bit more!

2. Jan 22, 2014

### Staff: Mentor

I don't know the answer to your question but there's a classic book that may:

Principles of Underwater Sound by Urick

In chapter 5 (page 100+) there's a discussion on spreading loss from a point source, and from a line source.

One thing to be aware of is the distinction between intensity and decibel level. Intensity for a point source decreases by r^2 whereas decibel levels use logarithms ie transmission loss = 10 log(r^2) = 20 log (r) in decibel units.

3. Jan 22, 2014

### JoaoCorvina

Thank you for the correction! I meant intensity!