Question For All You Asw And Nuke Guys.

[SDirickson 0]

One of the questions on my Naval Science final had to do with the basic characteristics of active and passive sonar. It was something like;

 

Passive sonar has which properties:

A. Stealthy

B. Longer Range than Active

C. (Blatantly Wrong)

D. (Blatantly Wrong)

 

Now, I got a bit confused here. I even went down and asked my instructor about it. He should have known, after all, he's a HH-60B pilot and does ASW work for a living. He told me, and I quote, "There is one obviously correct answer."

 

I knew A was correct, because passive sonar doesn't send any sound waves into the water, it's basically just listening. But then, I thought passive had a longer range as well. Ignoring the whole thermal layer, and sound waves bouncing along it and all the other quirks of sound when travelling through water, I thought active could only work to a certain distance, before the sound lacked the energy to bounce back. Passive, however, could detect an active burst from twice as far away as the pinging sub.

 

I think I put down A, just because I didn't feel like arguing any more, but shouldn't both answer choices have been correct?

[Skater 0]

You came to the right place, because I am a Sonar Tech!

 

Technically, A and B are correct. However, the safe answer is A. The reason is that Active transmission has the capability to give longer range under certain conditions that I will not go into here. Also, you will get more information, especially for targeting purposes, at longer range with active transmission than you would with passive, and you would get that information very quickly. Passive listening can get you info, over a long period of time, and you can stay quiet and stealthy. You can move fast while using active, and still get usable info. You cannot transit at high speed using passive and expect to get anything in return.

 

Passive listening has it's pro's and con's as does active transmission.

 

Given a choice, I would stay passive, firm up the contact, stay stealthy, get a firing solution, maneuver the boat, fire off axis, turn the fish with the wire, and go active on the torpedo when 145 degrees off of actual bearing. But that's just me. :)

 

-Skater

[Beer 0]

I believe that SDirickson believes that because of the 2PL (out and Back Propagation Loss) for the Active Sonar equation, it only has 1/2 the range as Passive. This is not the case. However I would agree that in most cases Passive has longer ranges than Active (so the distractor answer "B" is an inviting choice).

 

A perfect example of a case where Active has better range than Passive (therefore removing "B" as a viable answer) would be tracking a newer Diesel underway submerged with DIFAR bouy's. A DICASS (Active) in the same location as a DIFAR would likely have greater detection range than the Passive DIFAR.

 

Why? The sub is quite (SL is low), and the noise from it is scattered and absorbed, thus does not make the detection threshold of the DIFAR; the Active DICASS has a SL that is high, and can make the trip out and back despite some scattering and absorption and exceeds the detection threshold. Because the SL (the Active PING) is high it can take the 2PL hit on the Active equation and still meet detection requirements.

 

LOL Don't worry if ya get your wings, your NATOPS written Exams will be multiple choice too, with even better distractors! B)

 

Cheers

Beer

[Seawolf 0]

Damn Beer, That was beautifull it brought tears to my eyes. ;)

 

A:Stealth is the correct answer young grasshopper.

[SDirickson 0]

Alright, you've sold me. You're right, Beer, I was thinking about the propagation loss. Just like using radar, I thought that passive had twice the range because it could hear the pings from farther than they would return to, so to speak.

 

Now, question number two, what is it called when the sound, bouncing between thermal layers, allows you to hear it from specifically distanced rings around the sub. Convergence? Something like that? If I remember, I think it was like 20 knots out and 60 knots.

 

I'll be honest, all my sub knowledge comes from Mr. Clancy, so I'm definately a beginner.

[Beer 0]

Convergence Zones or CZ for short, ask your instructor about it for ranges.

 

Cheers

Beer

[Dagger 21]

and remember get a screw count so you don't pop some poor liner with an ADCAP(like i tend to do in SC)

[Guest MrMudd]

You guys gave me Wood.

 

I love ASW warfare.

 

Ive been doing the Sonalysts Subcommand for a few years now and am pretty good if not a deadly apponent online.

 

I have done some work on naval projects in my civillian job and had the opportunity to spend a week on an attack boat. The young Sonar Crewman could run circles around me. And i was the Technical rep providing his equipment!

[SDirickson 0]

I'll admit, I wanna go aviation, preferably F/A-18's. But now, I won't be so disappointed if I get an ASW aviation slot, or go nuke or SWO with a destroyer.