Noob question on sonar contacts

[desertisland]

I have been wanting to ask this question for a while now:

When using the broadband sonar with towed arrays, is it true that, for every true contact, you will always receive a false contact opposite of the true one at exactly the same angle from your ships's direction?

I guess this is one of the properties of wave motion? Correct me if I'm wrong, I'm intrigued.

I just need to confirm if there will always be a mirrored false contact. Thanks! :hmm:

[Captain Nemo]

When using the broadband sonar with towed arrays, is it true that, for every true contact, you will always receive a false contact opposite of the true one at exactly the same angle from your ships's direction?

I guess this is one of the properties of wave motion? Correct me if I'm wrong, I'm intrigued.

I just need to confirm if there will always be a mirrored false contact. Thanks! :hmm:

That is correct. I can't quite remember the reason why this happens, but to ensure I always assign a tracker to the correct contact, I make a 10 degree turn and watch which one moves with the turn and which one doesn't. The one that doesn't is the true contact.

Nemo

[Aegeus]

Way far from being a sonar expert but i think that is always the case with TA broadband or narrowband.

Dont mean to hijack the thread but here is another sonar question.
I found out that is possible to deploy both your TAs will that help in getting a better fire solution especially if you deploy them in a different length?

By the way first post here so glad to find you guys:up:

[Captain Nemo]

Welcome to the forum. Not sure that you can deploy both TA's at the same time, how would you select starboard and port individually at the sonar station? They also might interfere with each other. Never tried it though to confirm this.

Nemo

[desertisland]

Dont mean to hijack the thread but here is another sonar question. I found out that is possible to deploy both your TAs will that help in getting a better fire solution especially if you deploy them in a different length?
[raise hand]
You can release both TAs in Seawolves but not 688s. Read somewhere (manual? yes I read it cover to cover] that one is only the backup for the other, releasing both will do you no good nor harm except the risk of wrecking both at once.

I also think it is better to keep you TA short. Reduces time for it to snap in line with the ship's direction so you can id the false contact faster.

[Dr.Sid]

Towed array is string of individual hydrophones (many, more then 10).

Direction of incoming sound is derived from time delay of signal on individual hydrophones. If rear hydrophones receive the sound before front ones, the sound source is behind the array. If the time delay is distance between hydrophones divided by speed of sound it means the target is exactly behind the array. If the delay is shorter by sin(45)=0.707 it means the target is 45 degrees from the array axis, if the delay is 0 it means the target is 90 degrees and so on.

With just this you can't tell if the target is left or right. So there isn't in fact any mirror contact. You just don't have the idea if the contact is left or right, so both are displayed. Check FFG sonar, it only shows half the circle.

With sphere and hull arrays this problem does not exist because sounds does not reach all the hydrophones, especially not those on the opposite side of the boat.

[Aegeus]

Welcome to the forum. Not sure that you can deploy both TA's at the same time, how would you select starboard and port individually at the sonar station? They also might interfere with each other. Never tried it though to confirm this.

Nemo
Thanks for the welcoming:)
If you go at the control station and select port or starboard on the TA selection switch you get info from the selected array in the sonar station.
I first found it on a 688 dont know if it works on a Seawolf.
My thought was that if you deploy them in a different length you would end up (?)with two different bearings at the target at the same time which is good for TMA i think.
I am noob so dont know much just learning at the moment

Edit
I ve just tried it on a Seawolf and you cant deploy both

[sonar732]

The main thing to think about with deployment of towed arrays is this....tactics!

The TB-29 is the more sensitive, while the TB-16 has a higher washout speed. In the book the TB-29 is listed as starboard and the 16 is port.

[desertisland]

Direction of incoming sound is derived from time delay of signal on individual hydrophones. If rear hydrophones receive the sound before front ones, the sound source is behind the array. If the time delay is distance between hydrophones divided by speed of sound it means the target is exactly behind the array. If the delay is shorter by sin(45)=0.707 it means the target is 45 degrees from the array axis, if the delay is 0 it means the target is 90 degrees and so on.
Thank you, Dr. Sid, for your answer. It makes sense to me. :up:

In other words, with 4 constants which are the distance between each receptors, the time-lag between each receptor's receiving the signal, the speed of sound, and the TA's aligment, we could determine 2 possible directions of the sound source?

And if all receptors receives the signal at the same time, we could tell that the source is either 90 degrees to the left or the right?

[desertisland]

This is fun. Let me indulge myself a little more. A model for the towed array:

Ask 10 school boys to stand in a row, each 5 meters apart and carries a flag in hand.

Tell the boys to raise the flag if they feel the wind against their cheeks.

By the time lag between each raised flag, and the sequence in which they are raised, we could determined the direction of the wind. But we would get 2 possible solutions since the boys are not asked to tell which cheek is feeling the wind.

[Dr.Sid]

This is fun. Let me indulge myself a little more. A model for the towed array:

Ask 10 school boys to stand in a row, each 5 meters apart and carries a flag in hand.

Tell the boys to raise the flag if they feel the wind against their cheeks.

By the time lag between each raised flag, and the sequence in which they are raised, we could determined the direction of the wind. But we would get 2 possible solutions since the boys are not asked to tell which cheek is feeling the wind.
Well this could work only if you new speed of the wind :|\\ But generally that's it.
Well in fact it is done in slightly different way. Signals are summed with preset delay which amplifies signals from specific direction. It's called 'array steering' or 'beam-forging'. For BB display many such virtual beams are forged all the time, each for one bearing. It really takes a lot of math to simply see 'ah, there is something loud on bearing 030' :|\\

Edit: I should quit smoking ..

[desertisland]

Do quit, I heard it's bad for health. :)

Another question:

Since the "pair" of contacts are not detected separately but deducted from a single group of data, why doesn't the computer specify them as "pairs" to simplify matters? Especially when you get multiple contact and it can be hard to tell which pairs with which? If they are group into pairs, the captian (or whoever is in charge of such matters) will remember to kill one of the twins. Wouldn't that be simpler?

Oh and I do believe the actual process is more complicated than this. Multiple sounds may overlap in their time of arrival, further complicating matters...:hmm:

[Dr.Sid]

Check FFG sonar, it works more or less as you described. What screens and systems are used on real subs and ships is not known anyway (I mean not told).

For overlapping sounds there is narrow-band, which means even more math with Fourier transformation. With that you can follow one frequency .. and it should be possible to choose some which does not conflict with anything else.

Again .. how much this is used IRL is hard to tell. From what I read you can assign auto-markers even for BB contacts, especially because they can measure actual rate of bearing, even if the bearing changes too slowly to see it on the screen.

But to auto-follow contacts without being fooled by crossing lines you have to follow concrete NB line I guess.

[Wim Libaers]

When using the broadband sonar with towed arrays, is it true that, for every true contact, you will always receive a false contact opposite of the true one at exactly the same angle from your ships's direction?


Almost. The ship's direction is not important, the array direction is. This matters in turns, where ship and array direction are different.

[desertisland]

Almost. The ship's direction is not important, the array direction is. This matters in turns, where ship and array direction are different.

Thanks for pointing that out, Wim. A more accurate description would be "the alignment of the towed arrays".

[Bellman]

A ''Noob question'' - really ? ;)

[desertisland]

A ''Noob question'' - really ? ;)
Really:oops:

I'm the bookish type that talk the talk but don't walk the walk. :doh:

[desertisland]

This is useless in game, just fun to know:

cos A=b/b'

b=(distance between receptors) / (speed of sound in water)
time for sound to travel between receptors while doing so along the array
a constant

b'=time lag between the receptors' detection of sound
what the towed array is designed to find out

A=angle of contact from the string of receptors
with this we get a pair of possible bearings

In practice:

arccos b/b'=A

What to do with A is determined by the sequence in which the receptors receive the sound signal.

If the front receptors receive the sound signal first:
contact bearing = (0 + A) or (360 - A)

If the end receptors receive the sound signal first:
contact bearing = (180 + A) or (180 - A)

[Travis Reed]

I would think that having two TAs out simultaneously could lead to uhm...interesting entanglements...thus, it' not done IRL (at least, no one talks about it being done IRL...)

[desertisland]

I would think that having two TAs out simultaneously could lead to uhm...interesting entanglements...thus, it' not done IRL (at least, no one talks about it being done IRL...)

I'm impressed my TA was never spun into a complex knot with my radio wire. Must be the extra special lubricant they applied to the cables...:up:

[sonar732]

I would think that having two TAs out simultaneously could lead to uhm...interesting entanglements...thus, it' not done IRL (at least, no one talks about it being done IRL...)
I'm impressed my TA was never spun into a complex knot with my radio wire. Must be the extra special lubricant they applied to the cables...:up:

:rotfl::rotfl::rotfl::rotfl::rotfl::rotfl:

[Gorshkov]

One basic question about sonar detection ranges in DW: At what distances can each DW submarine detect others under ideal sea conditions using TA, hull and cylindrical sonars???

Maybe some links to appropriate data would be the quickest answer?

[goldorak]

It depends on the environment (SSP data), time of the year, wether you're playing in littoral waters or in the deep ocean.
It depends also againt whom you're playing, Kilo subs are deadly quiet and can come very close, something under 5nm without being detected.
Nuclear subs are more noisy so are more easily detected.
If you have convergence zones, you might detect a contact out to 30 nm.

The point is this : low frequency waves travel the furthest, the medium frequency not as much and last high frequency waves.
So your primary means of detection is to use the towed array which is tuned to detect low frequency noises.

[SeaQueen]

It depends on the combination of many factors including including the target and receiver depth, bottom type, the geography of the bottom (seamounts, for example, often block convergence zone propagation) and sound speed profile. The mission editor will draw sensor range rings. I use those frequently both in designing missions and as a tactical decision aid.

One basic question about sonar detection ranges in DW: At what distances can each DW submarine detect others under ideal sea conditions using TA, hull and cylindrical sonars???

Maybe some links to appropriate data would be the quickest answer?