Technique for getting range with hydrophones

PurpleCity · 01-25-09, 03:32 PM

When I play with map contacts on, my sound man appears to know the approximate range and bearing of any sound contact. He also seems to know if the contact is closing or moving away.

Is he sending an active sonar ping, or is there another technique for estimating the range?

Soundman · 01-25-09, 03:35 PM

He is pretty good huh? No, he is using passive sonar. The bearing is easy, but yes, they are also pretty good at estimating range.

PurpleCity · 01-25-09, 03:56 PM

Thanks.

Is this realistic, could a sound man actually estimate range just by listening to the screws? I'm assuming they're comparing amplitude and pitch against memory.

Fish40 · 01-25-09, 05:39 PM

I might think a skilled soundman may be able to make a pretty good guestamate as to the range of a target by listening to how far away/close the ship is. A more reasonable and accurate way would be to actively ping a target, and get the range that way. I've done this myself on several occasions. But beware!! If you use active sonar with escorts present, they can and do hear it! I make it a habit to only ping lonely merchants.

RSColonel_131st · 01-26-09, 06:21 AM

In my opinion (without knowing too much about how those old hydros worked), the sound you get from the speaker/headphones is an electric current. It will be louder (more current/voltage) when it's closer, and less when it's further away. Does that sound plausible?

If so, I wonder why they didn't match the hydrophones with a pair of calibrated volt meters, going of known volume levels for near/far away merchants and warships.

Hitman · 01-26-09, 06:31 AM

Quote:

If so, I wonder why they didn't match the hydrophones with a pair of calibrated volt meters, going of known volume levels for near/far away merchants and warships.

They did. That's represented by the green lamp that lights when a contact is made.

Quote:

Is this realistic, could a sound man actually estimate range just by listening to the screws? I'm assuming they're comparing amplitude and pitch against memory.

Well more or less yes, sound intensity obviously increased in principle when the sound source is closer BUT the sound transmission in the sea water is a real headbreaker when it comes to giving exact solutions. A good proof of it is how even today submarines can still stay unlocated if properly hidden below thermal layers and such. That means that you could hear a strong contact for a distant target if the proper sound conditions happen, and inversely not even hear a close contact.

As a 688i/Sub Command/Dangerous Waters player I have readed a lot about the matter, and the only conclusion I have comed upon is that you hardly can draw any conclussions at all

, so variable and strange is the sound propagation thorugh water.

groomsie · 01-26-09, 01:26 PM

The information isn't perfect always (I've ovserved a target appraching in the scope and sound reports it as moving away, etc), nor should it be. But, decent-to-good soundmen can tell you quite a lot, especially if they have time to listen for a while (the information generally improves with time). Clues like the ones noted above (sound intensity for example) are used, but also they count revolutions on the screws and can judge speed; then factor in the relative rate of bearing change (bearing drift) with all the other information and they can make a reasonable guess as to range (ie: a high speed target with slow bearing drift and sound level is relatively constant is at longer range; a high speed target with slow bearing drift and sound level increasing is closing; a low speed target with rapid bering drift and constant sound is close and running "with" you...make sense?).

While I was a surface ship sailor, I did a lot of anti-submarine work during my time and can verify the sound characteristics of the ocean vary greatly. The submarine lives in and depends upon these characteristics to help maximize their advantages, so the sound men become very skilled at making a judgement on their own as to the speed, range, course, and type of contact. Add in the other elements (tracking party doing Target Motion Analysis is a big one) and a sub can tell a lot without even popping up the scope.

In many respects the bearing lines tell too much information if you are using them; you can pretty well nail many target locations using those alone. But there are other elements you don't get so I figure it washes out...

RSColonel_131st · 01-26-09, 03:55 PM

I actually wonder if bearing-only TMA was done back then with pen and paper. It would provide a perfect firing solution or at least a very exact fix for the last short periscope confirmation to be done. But bearing-only TMA on a plot of paper IMHO is not very easy to do.

01-25-09, 03:32 PM	#1
PurpleCity Loader Join Date: Jan 2009 Posts: 87 Downloads: 75 Uploads: 0	Technique for getting range with hydrophones When I play with map contacts on, my sound man appears to know the approximate range and bearing of any sound contact. He also seems to know if the contact is closing or moving away. Is he sending an active sonar ping, or is there another technique for estimating the range?

01-26-09, 01:26 PM	#7
groomsie Electrician's Mate Join Date: Jun 2008 Location: Stoughton, WI Posts: 140 Downloads: 50 Uploads: 0	I'd say it is fairly realistic... The information isn't perfect always (I've ovserved a target appraching in the scope and sound reports it as moving away, etc), nor should it be. But, decent-to-good soundmen can tell you quite a lot, especially if they have time to listen for a while (the information generally improves with time). Clues like the ones noted above (sound intensity for example) are used, but also they count revolutions on the screws and can judge speed; then factor in the relative rate of bearing change (bearing drift) with all the other information and they can make a reasonable guess as to range (ie: a high speed target with slow bearing drift and sound level is relatively constant is at longer range; a high speed target with slow bearing drift and sound level increasing is closing; a low speed target with rapid bering drift and constant sound is close and running "with" you...make sense?). While I was a surface ship sailor, I did a lot of anti-submarine work during my time and can verify the sound characteristics of the ocean vary greatly. The submarine lives in and depends upon these characteristics to help maximize their advantages, so the sound men become very skilled at making a judgement on their own as to the speed, range, course, and type of contact. Add in the other elements (tracking party doing Target Motion Analysis is a big one) and a sub can tell a lot without even popping up the scope. In many respects the bearing lines tell too much information if you are using them; you can pretty well nail many target locations using those alone. But there are other elements you don't get so I figure it washes out...

01-25-09, 03:35 PM	#2
Soundman Commodore Join Date: Jul 2006 Location: Orlando, Fl Posts: 617 Downloads: 60 Uploads: 0	He is pretty good huh? No, he is using passive sonar. The bearing is easy, but yes, they are also pretty good at estimating range.

01-25-09, 03:56 PM	#3
PurpleCity Loader Join Date: Jan 2009 Posts: 87 Downloads: 75 Uploads: 0	Thanks. Is this realistic, could a sound man actually estimate range just by listening to the screws? I'm assuming they're comparing amplitude and pitch against memory.

01-25-09, 05:39 PM	#4
Fish40 The Old Man Join Date: Aug 2006 Location: Yonkers, NY U.S.A. Posts: 1,507 Downloads: 154 Uploads: 0	I might think a skilled soundman may be able to make a pretty good guestamate as to the range of a target by listening to how far away/close the ship is. A more reasonable and accurate way would be to actively ping a target, and get the range that way. I've done this myself on several occasions. But beware!! If you use active sonar with escorts present, they can and do hear it! I make it a habit to only ping lonely merchants.

01-26-09, 06:21 AM	#5
RSColonel_131st Medic Join Date: Jan 2002 Posts: 164 Downloads: 0 Uploads: 0	In my opinion (without knowing too much about how those old hydros worked), the sound you get from the speaker/headphones is an electric current. It will be louder (more current/voltage) when it's closer, and less when it's further away. Does that sound plausible? If so, I wonder why they didn't match the hydrophones with a pair of calibrated volt meters, going of known volume levels for near/far away merchants and warships.

01-26-09, 03:55 PM	#8
RSColonel_131st Medic Join Date: Jan 2002 Posts: 164 Downloads: 0 Uploads: 0	I actually wonder if bearing-only TMA was done back then with pen and paper. It would provide a perfect firing solution or at least a very exact fix for the last short periscope confirmation to be done. But bearing-only TMA on a plot of paper IMHO is not very easy to do.