Reply by Rune Allnor September 27, 20062006-09-27
glen herrmannsfeldt skrev:
> Rune Allnor wrote: > > > glen herrmannsfeldt skrev: > (snip) > > >>There is a (fictional) book, "The Ninth Day of Creation", which > >>describes a top secret sonar system. In a quick description, it > >>sends out a whole spectrum of signals and analyzes the result coming > >>back. > > > The author is not a sonar guy, then. The problem with sonars, > > compared to radars, is the frequency-dependent noise and > > losses. Broad-band signals are all but impossible at all > > but the shorter ranges, simply because dispersion and > > frequency-dependent losses see to that only narrow-band > > parts of the signal can be detected. It's all about the water > > as transmission medium. > > I believe like other authors, it was done after interviewing > appropriate people in the field.
I hope so. The problem that there are several types of experts: - The operators who actually use the kits. These guys usually do not have the technical expertise to understand how the kit they use, works. They know how top operate it and what to search for in the data. - The technical maintenace people. They know the nuts'n bolts of the gear and the physical parameters of the signals. But they usually don't know hoe the kit is used. - The theoreticians. They know how set up a data processing scheme for the operatives, but they usually don't know how the kit is used during operations or how the gear looks like. No type of expert are likely to understand the full chain from system design, measurement and final analysis. And of course, everything is filtered through the author, inserting his or her misunderstandings and obfuscations everywhere.
> As well as I remember now, the > transmitted signal is fairly high power, to get above the noise. > That also means that everyone else knows where you are. (I believe > one then leaves the scene as soon as possible.)
One surely ought to...
> As I remember, > it was more like a frequency sweep, which would have other time > dependent effects, but maybe better than a broadband source.
There are plenty of signalling schemes around. All of which work (or not) at the grace of the oceanography.
> >>Not only can it detect the position of a mystery submarine, > >>but also enough to identify the country that owns it. (Presumably > >>by analyzing known submarines.) > > > Well, there is lots of myth and illiteracy regarding sonars. > > > The (fictional!) sonar system onboard the US sub in Tom Clancy's > > "The Hunt for Red October" is capable of doing something similar. > > In the book, the sonar computer analyzes the first data ever > > recorded of the Red October, and comes up with the technical > > details, like type of submarine. In another sequence, where the Red > > October slips away from the US sub, the sonar computer detects > > something that it classifies as some geological activity. > > > Neither type of automated decision-making are possible in the > > real world. > > In this case, there was an expert on the system, one who was part of > the development, on the sub at the time.
As consultant for Clancy?!? You have to be kidding! He did a very poor job, then. Or maybe not. To put it this way: If I were in the navy and asked to consult on a book on navy sonar systems, I would obfuscate the details about what the systems do and how things work, as much as possible. If you read the book carefully (or see the movie), you will note that the sonar operative, when explaining why they didn't detect "Red October" slip away, says something like "The computer system was originally designed for seismic applications. When it finds something in the data it doesn't recognize, it classifies it as magma." Note how carefully that's crafted: A navy guy can say that "I don't understand how this works, but I don't know seismic software." A seismic guy can say the same from the other direction. Of course, all of this is as pure BS as you will ever find it. Neither seismic or sonar data analysis is done that way. The problem is that "Red October" backfired, and now everybody believe that's how things are done, or at least ought to be done. Which, of course, adds nothing to making any actual progress in sonar technology. Rune
Reply by glen herrmannsfeldt September 27, 20062006-09-27
Rune Allnor wrote:

> glen herrmannsfeldt skrev:
(snip)
>>There is a (fictional) book, "The Ninth Day of Creation", which >>describes a top secret sonar system. In a quick description, it >>sends out a whole spectrum of signals and analyzes the result coming >>back.
> The author is not a sonar guy, then. The problem with sonars, > compared to radars, is the frequency-dependent noise and > losses. Broad-band signals are all but impossible at all > but the shorter ranges, simply because dispersion and > frequency-dependent losses see to that only narrow-band > parts of the signal can be detected. It's all about the water > as transmission medium.
I believe like other authors, it was done after interviewing appropriate people in the field. As well as I remember now, the transmitted signal is fairly high power, to get above the noise. That also means that everyone else knows where you are. (I believe one then leaves the scene as soon as possible.) As I remember, it was more like a frequency sweep, which would have other time dependent effects, but maybe better than a broadband source.
>>Not only can it detect the position of a mystery submarine, >>but also enough to identify the country that owns it. (Presumably >>by analyzing known submarines.)
> Well, there is lots of myth and illiteracy regarding sonars.
> The (fictional!) sonar system onboard the US sub in Tom Clancy's > "The Hunt for Red October" is capable of doing something similar. > In the book, the sonar computer analyzes the first data ever > recorded of the Red October, and comes up with the technical > details, like type of submarine. In another sequence, where the Red > October slips away from the US sub, the sonar computer detects > something that it classifies as some geological activity.
> Neither type of automated decision-making are possible in the > real world.
In this case, there was an expert on the system, one who was part of the development, on the sub at the time. -- glen
Reply by Rune Allnor September 24, 20062006-09-24
glen herrmannsfeldt skrev:
> Rune Allnor wrote: > (snip) > > > The general idea behind radar and active sonar systems, is that > > you send out a signal -- and thus have knowledge about what that > > signal looks like, since you control the transmitter -- and search > > for a copy of that same signal in the recieved data stream. > > > In the usual terminology x[n] represents a measured signal > > while h[n] is some system response that you have designed. > > There is a (fictional) book, "The Ninth Day of Creation", which > describes a top secret sonar system. In a quick description, it > sends out a whole spectrum of signals and analyzes the result coming > back.
The author is not a sonar guy, then. The problem with sonars, compared to radars, is the frequency-dependent noise and losses. Broad-band signals are all but impossible at all but the shorter ranges, simply because dispersion and frequency-dependent losses see to that only narrow-band parts of the signal can be detected. It's all about the water as transmission medium.
> Not only can it detect the position of a mystery submarine, > but also enough to identify the country that owns it. (Presumably > by analyzing known submarines.)
Well, there is lots of myth and illiteracy regarding sonars. The (fictional!) sonar system onboard the US sub in Tom Clancy's "The Hunt for Red October" is capable of doing something similar. In the book, the sonar computer analyzes the first data ever recorded of the Red October, and comes up with the technical details, like type of submarine. In another sequence, where the Red October slips away from the US sub, the sonar computer detects something that it classifies as some geological activity. Neither type of automated decision-making are possible in the real world.
> It seemed to me almost like taking > a Fourier transform to find the shape of the object reflecting the > signal.
It could be some sort of reflection-based tomography, much like an Inverse Synthetic Aperture Radar system. The problem with this, is that the medium where the signal propagaties back and forth between the sonar and target, is more or less random, at least on the scale needed to do any sort of phase coherent processing. While it ought to be possible to achieve _something_, it will by no means be comparable to ISAR. Rune
Reply by glen herrmannsfeldt September 24, 20062006-09-24
Rune Allnor wrote:
(snip)

> The general idea behind radar and active sonar systems, is that > you send out a signal -- and thus have knowledge about what that > signal looks like, since you control the transmitter -- and search > for a copy of that same signal in the recieved data stream.
> In the usual terminology x[n] represents a measured signal > while h[n] is some system response that you have designed.
There is a (fictional) book, "The Ninth Day of Creation", which describes a top secret sonar system. In a quick description, it sends out a whole spectrum of signals and analyzes the result coming back. Not only can it detect the position of a mystery submarine, but also enough to identify the country that owns it. (Presumably by analyzing known submarines.) It seemed to me almost like taking a Fourier transform to find the shape of the object reflecting the signal.
> Since you know what signal you transmitted, you have some > idea about what you will recieve. Consequently, you can design > a system response h[n] that helps you detect the transmitted > signal in your measured data stream.
> Once you have designed a h[n] and measured a x[n], you > convolve (not multiply) the two in order to estimate whatever > parameters are interesting to you.
I would have thought you might want an inverse convolution. -- glen
Reply by Jim Thomas September 21, 20062006-09-21
Dilip V. Sarwate wrote:
> "can't praise .. too highly on that count..." > > is. To my tin ear, it sounds like saying that a moderate > (or even a faint) praise is quite adequate on that count, > which is surely not the meaning intended. Ah well, I > suspect that the phrase is well-fixed in the idiom by now.
This was the basis of a skit done on Saturday Night Live maybe ten years ago. In the skit, the nuclear reactor manual said "You can't add too much water to a reactor going into meltdown." It may have involved Will Farrel, but I'm not sure. It was a long time ago and I only saw it once (but it was amusing!) -- Jim Thomas Principal Applications Engineer Bittware, Inc jthomas@bittware.com http://www.bittware.com (603) 226-0404 x536 If a job's not worth doing, it's not worth doing right.
Reply by Rune Allnor September 21, 20062006-09-21
forums_mp@hotmail.com skrev:
> Rune Allnor wrote: > > For starters, you folks are good. Wow!!
Some people are. As for myself, I find that comp.dsp is one of few places that slows down my forgetting stuff I once knew.
> > Once you have designed a h[n] and measured a x[n], you > > convolve (not multiply) the two in order to estimate whatever > > parameters are interesting to you. > Your comment "not multiply" - leads me to believe you're referring to > the time domain here - since time domain convolution is multiplication > in frequency. My beliefs correct?
Yep. I tend to discuss time domain unless we explicitly have agreed that we discuss frequency domain. And old habit of mine. Rune
Reply by Jerry Avins September 21, 20062006-09-21
Randy Yates wrote:

   ...

> Jerry, you're a joy to have around!
<blush>
> I never understood the > relationship and meaning of these words before! Like many people, I > would've thought "inflammable" means NOT flammable! Doh!
The prefix "in" usually means "not" as in "insensitive"; equivalent to "un" as in "unwieldy". Sometimes it is equivalent to "en: as in "enrage". "Inflammable", "inflammation" and "incite" are examples. ...
> Inflammable air, the old chemical name for hydrogen. > 1913 Webster
An old name for oxygen was "dephlogisticated air". Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
Reply by Randy Yates September 20, 20062006-09-20
Jerry Avins <jya@ieee.org> writes:

> Rune Allnor wrote: > >> It took a long time before I understood what "invaluable" and >> "inarguably" meant... > > "Inflammable" is confusing to enough people that the Department of > Transportation requires that trucks with inflammable cargo be labeled > "flammable", a non-word that might have made it into some dictionaries > by now. > > Jerry
Jerry, you're a joy to have around! I never understood the relationship and meaning of these words before! Like many people, I would've thought "inflammable" means NOT flammable! Doh! In fact, my little dictionary bar states: "The Collaborative International Dictionary of English v.0.48" Inflammable In*flam"ma*ble, a. CF. F. inflammable. 1. Capable of being easily set fire; easily enkindled; combustible; as, inflammable oils or spirits. 1913 Webster 2. Excitable; irritable; irascible; easily provoked; as, an inflammable temper. 1913 Webster Inflammable air, the old chemical name for hydrogen. 1913 Webster -- % Randy Yates % "Watching all the days go by... %% Fuquay-Varina, NC % Who are you and who am I?" %%% 919-577-9882 % 'Mission (A World Record)', %%%% <yates@ieee.org> % *A New World Record*, ELO http://home.earthlink.net/~yatescr
Reply by September 20, 20062006-09-20
Jerry Avins wrote:

> > I did it for you before I saw this message. Should I be sorry?
Not at all. I can't imagine how much damage I'd do if I had just half of your knowledge base. Off to order Rick's book. It appears he's a also a regular here.
Reply by September 20, 20062006-09-20
Rune Allnor wrote:

For starters, you folks are good.  Wow!!

> > Once you have designed a h[n] and measured a x[n], you > convolve (not multiply) the two in order to estimate whatever > parameters are interesting to you.
Your comment "not multiply" - leads me to believe you're referring to the time domain here - since time domain convolution is multiplication in frequency. My beliefs correct?