Side scan sonar

In principle, the term SONAR means a horizontal scanning device. Echosounders mean vertical scanning.

Basically they are the same stuff, but in shipbuilding / shipdesign one differentiates between the high resolution (often long range / low frequency) SONAR for Mil. and scientific purpose and the much cheaper Echosounder for lower end applications.

But it is not completely wrong to call a fish finder sonar as well.

Regards
Richard

 

Side scan differs from 3-D swath mapping in several aspects, most importantly that side scan looking for the "shadow" of items proud of the sea floor away from the track of the tow-fish, while a sounder is measuring the height of the bottom directly under the xducer and side lobes then developing a plot over multiple pings. Both can be used develop 3-d bathymetry.

See these sites for the differences between side scan and multi-beam swath theory:

http://www.absoluteastronomy.com/topics/Side-scan_sonar

http://www.antarctica.ac.uk/bas_research/instruments/swathbathymetry.php

 

Thanks Richard, I assumed it to be something like that. To me, sonar is what a sub uses to observe where it is going and destroyers to find the sub.

In my "computer life" trying to get a very rewarding order from a dredging company, I designed and built a tube shaped object that was to be towed under a large RIB. It contained an array of 8 ultrasonic transducers that were actuated sequentially. The signal was recorded together with position data and software later made that into a 3D picture of the seabed.
I used a towed instrument because the RIB was in choppy seas most of the time and a fixed transducer supplied unreliable data. We called it a depth scanner, but I guess you would call it sonar now. Jehardiman's links show more or less similar devices for the same purpose.

But guys from (I think) Simrad with more experience made a fixed device that supplied longitudinal and transverse angle reference signals. With that plus the depth data the software could calculate the actual depth even when the RIB had swayed violently during the scan.

The client was skeptical about a towed device from the beginning, so we only got the order for a number of very expensive industrial computers.

 

The towed / submerged device has the advantage of staying in calm conditions, of course.

There are "forward scanning" sounders on the market since more than 15 years now, but I still have not seen a clear, crisp picture produced by them. (til 2007)

After all, one could say look at the price tag. Is it over 50.000€ it´s a sonar.

 

Humminbird and now also Navman have 3D side scanning echo sounders.. Kind of poor man's version of a real side scan sonar. Limited range but enough for fishing and diving in shoals. Gives picture good enough to find small anchor or fallen fishing rod in 20m water..

edit: not sure about the Navman but Lowrance has another such device..
edit2: also found an interesting site for Humminbird owners http://forums.sideimagingsoft.com/ to boost their side imaging units..

 

Sound and infra red

http://gdr-isis.org/Kiosque/theses/Christophe-Collet-20000511.html

This study was done in Brest by CNRS, University of Bretagne, ENS, and Ecole Navale

You will learn, how, from 1990 to 2000, was improved marine acoustic imagery (sonar), by using a statistical discrimination of additional layers, like infra red.


So the real question is:

How deep is the pocket for the project ?

 

That was at least 120 dK !



For our peers not so familiar with the SI units:

http://www.boatdesign.net/forums/hy...c-generator-create-jobs-31205.html#post338909

a short extract:

May I suggest that we honor the master of drivelling, the drivel artist and guru Kistinie by naming the universal drivel unit after him. In order to display the mediocre drivelling produced by the rest of us on the same instrument, the scale would have to be logarithmic.

So, lets unite on the common unit "dK" (deciKistinie). It is just an unfortunate coincidence that it is pronounced "dekay", so any associations to the mental status of the priest of drivel is unintentional........

 

120 dK ?
Yes, why not...

Did you notice that Joe can do his own software development.
I would not bet he is unable to de-hum a sonar image with an added IR image.

In this case, you will get an additional 0 dK Apex.
120 dK + 0 dK = ? (Take care, dK is a Ln quantum scale)


A 2010 dK question for you Apex :
Do you know what "Ecole navale" is ?

 

http://www.oceanecology.ca/sidescan sonar.htm
Has a nice overview of the subject. The Ocean Engineering course I'm taking has covered the theory in some detail, and I have to admit that the math is more than challenging to the old brain!

I'm hoping to learn more about the algorithms used to develop the image. (There are some open-source software packages that do this)... All we need is an open-source towfish project!

 

Well said TerryKing !
Thanks.


...Open ...

Open is a Magic word, to see new things

 

You have an interesting range of writing styles Kristinie.

I think you might enjoy writing a novel. And you would probably find yourself being quite good at it.


I see you don't worry too much about being attacked in public. That's good; too many people take themselves way too seriously.

Side scan sonar is on one avenue being considered for this project, and yes we do have the capability to integrate other sensing devices with the sonar and other images. In ways that others with direct experience have never thought of before.

Thanks for all the help ya’ll are providing.