Broadband vs narrowband sonar
 

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.

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.

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.

: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.

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 :88)

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?

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...

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.

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.

Wow, I always figured this forum would be watched but how did the figure out the real person behind Bubblehead?

I suppose the did and I.P. check and traced it that way aswell as you saying which sub you served on and when.

Respect to you guys, you have helped a lot with the understanding.

After reading related chapters from Uric's Princleps of underwater sound, Rip's statement looks solid. It's simple matter of what is dominant in the signature.
Without cavitation NB signals dominate total radiated spectrum, even for slow moving surface ships. NB will have major advantages, by telling what is noise and what is signal.
With cavitation (which is normal for surface ships at all but minimum speeds) the broadband noise dominates and covers all the lines. In such case NB will be of little advantage, if any.
Still exact amounts are mystery .. and big no-no from experts I asked. :arrgh!:

A lot of this information I've pieced together from various books I've read. It amazes me that some of this stuff is even remotely sensitive. For example the BSY-2 on the Seawolf uses a network of 70 68030 processors. 68030 are ANCIENT! These are the processors that were in the original MACs. The processors we use at work are orders of magnitude faster. I guess my point is, the technology isn't that special and doesn't need to be so secret, but the application of the technology should be. I.E. missions and operations.

Anyway, this is all off my original topic. Thanks Rip and Dr. Sid. I think that fills in the missing pieces in my mind. But now I am going to be compelled to create a little simulation to prove out these concepts. That curiosity thing just sucks some days.

I don't think that the technology itself is so secret, it's the real world efectiveness of it what is top secret, i.e. what they can or can't detect, what they can or can't hide, etc. Processor power is one thing, but that power might be sufficient if the data the sensors can collect is already detailed enough, or inversely, more processor power might be unnecessary because the current sensor technology can't provide more accurate data to be processed.

Besides, they probably used 70 of those (simple) processors at a couple of 10s of MHz, instead of lets say a more modern (single) P4 cpu at some Ghz, to make the processing parallel instead of serial.

We used to have little books called piping tabs which had every major system laid out in great detail. We used these when we had to shut down a system and tag other valves etc... so they would not be operated in order to maintain safety and perform whatever pm or repair necessary. I went to a garage sale and in a book bin for 50 cents was a piping tab for the Richard B. Russell SSN-687. I bought it from the lady and asked her where she got it and she told me it was her ex husbands who was a Mare Island naval shipyard worker.

At my exiting interview i was told that a 20 year federal prison sentence happens to those who would be caught with schematics of a nuclear submarine.

Even myself here on this subsim site, I want more accurate details about stuff especially sonar when it comes to playing this game, but not at the expense of having classified info being divulged. But now about those Russian boat (he he) I will take all the info I can get, too bad we do not have a Russian sub sailor here who we can pump for info....:D