Broadband vs narrowband sonar

[Shadowmind]

I recently tried the RA mod and it models broadband vs. narrowband contacts differently than the LWAMI mod. In LWAMI 3.08 it seems that contacts appear on narrowband long before you can pick them up on broadband. I didn't think about it much at first and I've been playing with the LWAMI mod for several years.

Recently I tried the RA mod and liked the idea that contacts showed up in broadband long before I could accurately detect their tonals. So I started to dig into it. I've never been on a sub, I don't claim to be a sonar expert, but I do a lot of image/signal processing in my job. So I threw together some graphs to prove out my concept.

It was easier if I just threw everything into a PDF and linked to it. Let me know what you think. Am I totally off base. Is there some fundamental concept I am missing?

Thanks.

[Dr.Sid]

First I think you get wrong conclusion in this: signal only consist of tonals. It's not true, it also consist of wide-band signals, ie noises. Those are hard to see on NB display but they add to total BB signal strength. This plays into BB sooner then NB theory.

Also you should use some different displays for NB .. those from matlab indeed does not look to good and the signal indeed can't be seen very well. Consider longer time window averaging which will cancel noise, also the noise in the sea is not uniform, nor are the tonals. So there can be many different situations.

If you had some really strong one high frequency tonal source, NB would help to differ it from mostly low frequenct background noise.

There is many BB sound sources in the sea. Only NB or aural evaluation can ID them as submarine.

I guess NB is first to identify contact as submarine. But BB could be first to make detection at all, with high false contact ratio. Also most books/movies follow this scenario.

But then I'm not submariner.

[Rip]

I will be a little vague to make sure I don't get too close to the line, but in general each platform has different NB to BB detection characteristics are different for types of contacts. Some specific tonals carry much better as well although they often don't get you much ID wise.

The rules change a good bit in different enviroments. When you are focusing on a specific target a good sonar team will know what tonals they will pick up in what order. They will also have some idea at what point they might gain BB contact.

[Shadowmind]

Originally Posted by Rip

I will be a little vague to make sure I don't get too close to the line

:hmm: Not sure what you mean by this. I didn't think my question was getting into classified areas.

Originally Posted by Rip

The rules change a good bit in different environments. When you are focusing on a specific target a good sonar team will know what tonals they will pick up in what order. They will also have some idea at what point they might gain BB contact.

So, in general, you would most likely pick up a contact in broadband first, and then over time start to sort out the tonals? Is there a difference in the sphere sonar vs towed arrays? One thing my simulation didn't model is the ability of different sensors to pick up signals. I've read that towed arrays, with the longer pick up area, is better at picking up lower frequency signals. But does that translate into a better ability to pick up tonals?

Thanks, This stuff just fascinates me.

BTW: Dr. Sid, I've enjoyed messing around with your ray tracing programs. They are very interesting.

[Dr.Sid]

Tonals come in all frequencies, that is not array dependent. Generally low frequencies travel far away .. but that is also the reason why there is more low frequency noise in the sea. So again, no general rule I guess.

In DW you first pick 50/60 Hz tonal .. that is more in towed array frequency range, rather than in sphere array range. But then DW does not take noise into account in NB.
Also, as I heard, many subs use 400Hz for basic electricity lines, because all the transformers can be much lighter and smaller like that. That would shift the tonal more into SA range, and away from dominant low frequency background noise.

PS: glad you enjoyed my tool

[Bubblehead Nuke]

Originally Posted by Shadowmind

:hmm: Not sure what you mean by this. I didn't think my question was getting into classified areas.

There is a MAJOR problem when you have served on a sub. You can, by admitting or dening something, PROVE something and thus compromise security.

It is the the difference of what you think you know and what you KNOW you know.

I might not tell you the truths, but by telling you want is wrong, tell you what is really right.

Does that make sense?

[Pingjockey]

I have to agree with bubblehead nuke... There are a lot of things you can't talk about...

Now back to the discussion, Rip has it right on the head, a good sonar team will what there looking for...

[Rip]

Originally Posted by Shadowmind

:hmm: Not sure what you mean by this. I didn't think my question was getting into classified areas.

So, in general, you would most likely pick up a contact in broadband first, and then over time start to sort out the tonals? Is there a difference in the sphere sonar vs towed arrays? One thing my simulation didn't model is the ability of different sensors to pick up signals. I've read that towed arrays, with the longer pick up area, is better at picking up lower frequency signals. But does that translate into a better ability to pick up tonals?

Thanks, This stuff just fascinates me.

BTW: Dr. Sid, I've enjoyed messing around with your ray tracing programs. They are very interesting.

The question didn't just the answer could. But didn't.

Some times broadband first but platforms that have been built with acoustic silence in mind will be seen with NB first and may in fact never give much BB levels. The TA is great at low freq tonals and the sphere at the higher freqs. The hull array is middle of the road. A lot can be gained by looking at what tonals are picked up first and what ones are missing or very week. You can even get to the point of knowing about a defect or special equipment on a specific platform and being able to identify/track a specific ship based on data collected by others when recording that platform. Digital tapes of all acoustic and electronic intercepts from a boat are gone over not just by ships crew but by other parties long after the mission has passed.

[Bubblehead Nuke]

Just FYI, for those of you who think there is not a line that we can not cross?

I was contacted some months ago officially (as in certified mail and a phone call to my unlisted number) that I was too descriptive on a few topics and was ... um.. reminded.. of the penalities of information disclosure.

I have been out for over a decade now and even someone like me can still compromise OPSEC if we say too much.

I was a lowly nuke who just pushed the sonar dome & torpedo room around.

These Sonar weenies er.. Techs, now if they cross the line they get REAL serious. They would probably get a knock on the door.