Diving With Active Sonar, what is safe?

[coleusna2006]

Conversion is as follows:
Intensity is power / area = power /(4*pi*r^2)
SPL = 10 log(intensity/reference intensity)
reference intensity in water is 6.7*10^-19

Use these values to back calculate range, or solve for power for a given range

My office mate solved the same problem using the sonar equation and arrived at nearly the same answer.

 

[tursiops]

reference intensity in water is 6.7*10^-19

??
What units are you working in? I'd have thought the reference intensity would be 1 microPascal.

 

[coleusna2006]

Tursiops, you are correct. The reference pressure is 1uPa but I am working in intensity vice pressure. It is easer to solve this problem this way. The reference intensity is 6.7*10^-19 watts/m^2. Reference intensity = (reference pressure)^2/(Density of sea water*speed of sound in sea water)

 

[tursiops]

Tursiops, you are correct. The reference pressure is 1uPa but I am working in intensity vice pressure. It is easer to solve this problem this way. The reference intensity is 6.7*10^-19 watts/m^2. Reference intensity = (reference pressure)^2/(Density of sea water*speed of sound in sea water)

I haven't played with this stuff for a long time, but I used to play with it a lot, on paper and in the water.
My gut feeling is your conversions are off somewhere and you are overestimating the effects on humans by a lot. I accept the TNO work, and I accept your statement that your sonar levels are 65W, so all that is left is your conversions and calculations.

 

[NAM001]

How are you converting your 65W source power to pressure?

Im not sure how either he is I think using the system power draw and comparing it to xmitt power. My sonar was about 200kw at 245 db. Measuring it differently it would 145 db depending on what 1db equals. Ill assume upa. power doubles every 6 db. So if his SPL is 167 and my sonar spl at 196kw was 247 then he is 80 bd down form 196kw .... That wold be 1/2 196kw, 13-14 times By that I would guess his power output is about 24 watts in the water at high freq and that is next to not there at all. That 24 watts in the water falls in line with a 65 watt overall system power draw. You have to remember that you could put 500 watts of 1 megahurt nthe water and not even know it it is there. frequency matters.

 

[coleusna2006]

I started this post to try to find out what was a safe SPL for a diver in the frequency range mentioned previously. Based on the second reply I found an article that I posted a link to. The answer is that 167dB is safe at this frequency. Thank you to everyone who posted a reference.

I don’t want to sound arrogant and that is why I did not post this until now but I am finishing my second masters degree in Engineering, this time from MIT. I am also a submarine officer, so it is fair to say that I also have practical expertise with sound in water and sonar as well. My calculations are sound for the liberal assumption of single arrival path.

For the comment of frequency mattering, of course it matters. Attinuation at the range I am talking about is neglagable.

That being said the sonar system has a few lower power level settings. With the 2.8W setting the safe range is between less than 1 m to about 2.6m (I don’t have my calculations in front of me.

 

[tursiops]

I started this post to try to find out what was a safe SPL for a diver in the frequency range mentioned previously. Based on the second reply I found an article that I posted a link to. The answer is that 167dB is safe at this frequency. Thank you to everyone who posted a reference.

I don’t want to sound arrogant and that is why I did not post this until now but I am finishing my second masters degree in Engineering, this time from MIT. I am also a submarine officer, so it is fair to say that I also have practical expertise with sound in water and sonar as well. My calculations are sound for the liberal assumption of single arrival path.

For the comment of frequency mattering, of course it matters. Attinuation at the range I am talking about is neglagable.

That being said the sonar system has a few lower power level settings. With the 2.8W setting the safe range is between less than 1 m to about 2.6m (I don’t have my calculations in front of me.

LOL. Yes, please don't sound arrogant. I used to teach in that program at MIT.
Check your calculations and assumptions. Even submariners can make mistakes, and at some point you learn to trust your gut feelings. And my gut feeling is you are not there yet.
Out.

 

[coleusna2006]

LOL. Yes, please don't sound arrogant. I used to teach in that program at MIT.
Check your calculations and assumptions. Even submariners can make mistakes, and at some point you learn to trust your gut feelings. And my gut feeling is you are not there yet.
Out.

I would not have posted then if I had not double checked them. My office mate conducted the same calculations as well but used a the sonar equation, vice intensity, to solve the problem and arrived at the same answers that I did. Based on the content tone of your posts here, if I was you I would be hesitant “trusting my gut”

 

[Duke Dive Medicine]

@Duke Dive Medicine ?

Thanks for the shout-out Rob. I do not have the math chops to debate this with a couple of nukes. The first place I'd have gone would have been the Navy Diving Manual and that's already been mentioned.

Best regards,
DDM