Author Topic: Optimal SI distance for recordings  (Read 6399 times)

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Offline Wingnutt

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Optimal SI distance for recordings
« on: September 01, 2011, 05:07:24 AM »
I would like to survey some artificial reefs where I fish at and record them for viewing at home.  I've noticed on my unit (798) when I get into slightly deeper water (around 75-100 ft) it becomes difficult to discern objects if I have the SI set at a high range due to the screen being smaller.  I'm curious, if I make a recording at those long distances, will it be easier to view on a large screen at home on Humviewer?  I would like to optimize my range and view/mark objects at home rather than on the water if possible but I obviously need to be able to see the objects.  My goal is to make as few passes as I can and still be able to see what I need to see... the 'targets' that I will be marking range in size and composition from concrete reef balls (maybe 4'X4' ft) to 200 foot steel ships.


Offline sonar2000

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Re: Optimal SI distance for recordings
« Reply #1 on: September 01, 2011, 09:16:54 AM »
Yes it will be a better display on humviewer or most any external viewer.
Something you might try is to turn contour on and get rid of the water column.
That way you will see a bit more right and left with a smaller side to side distance..
Contour on is a sellection in your sonar menu.
Chuck

Offline Roddy

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Re: Optimal SI distance for recordings
« Reply #2 on: September 01, 2011, 08:25:18 PM »
Wingnut:; Where are you tring to SI the reef at? Some states in the USA have charts of there man made reef on the www. I have found if you search outside of the posted limit of the reef there are somethings that were missed droped, and charted water depth can be way off. Good luck and enjoy Roddy
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Offline Wingnutt

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Re: Optimal SI distance for recordings
« Reply #3 on: September 02, 2011, 03:20:14 AM »
Thanks Guys!

Chuck, I have tried the contour mode.  It works... sorta.  IMO, there is an awful lot of distortion of the target.  For example, we have subway cars as part of our reef system.  Very easy to recognize... rather large metal rectangle (even on the small screen of the 798).... but when I put it in contour mode to see further out to the side, I can barely recognize the subway car anymore.  Of course, this is changing the view AFTER I have gone by it... not sure if it would be better if the contour mode was set before the pass.

Roddy, yes I do have the wreck charts.  Hard to remember life before the web, but I actually have the published reef guides that were available back in the day.  Also the updates from the web as structure was added.  The problem with them is in an area with a high target density, they will group many targets under one symbol or region.  I wanted to get more specific... mostly in the hopes of seeing areas to drift with less chance of loosing hook rigs.

Offline sonar2000

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Re: Optimal SI distance for recordings
« Reply #4 on: September 02, 2011, 06:40:59 AM »
Something else for SI.. The larger the target the better the shadow.
Small objects below 60 to 70 feet are difficult.
Try scanning with contour mode on....
Capture some picture (snapshots) and post for us also..
Sounds like you are making progress..
Chuck

Offline Humminbird_Greg

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Re: Optimal SI distance for recordings
« Reply #5 on: September 02, 2011, 06:48:16 AM »
Wingnutt,
That distortion is due to the changing water depth.  As the water depth changes, the water column area changes widths and so the amount of data taken from the middle of the standard (non Contour mode) display changes as well.  This shifts the data seen to the sides and causes the distorted looking images.  If the bottom were perfectly flat than there would be no distortion.

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

Offline sonar2000

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Re: Optimal SI distance for recordings
« Reply #6 on: September 02, 2011, 06:54:06 AM »
Exactly...so for his scans I would run contour on....this seems to help......
And for the deeper targets a tow fish will greatly help.
Look in the tow fish photos and see if you can build or have someone build you a fish..
Chuck
« Last Edit: September 02, 2011, 06:56:29 AM by sonar2000 »

Offline RGecy

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Re: Optimal SI distance for recordings
« Reply #7 on: September 02, 2011, 07:00:07 AM »
I really havent played around with the Contour mode too much, but this leads me to ask, Are they using a true Slant Range Correction or are they just stretchinf the data to fit the screen?  If they are using the Slant Range correction to calculate it, there would only be some distortion near the middle.  The farther out you get it should appear like normal.

Liek Greg said, I think Contour mode works best on flatter bottoms when the depth is not changing rapidly or drastically.  Otherwise, I would keep it off.

Robert
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Offline sonar2000

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Re: Optimal SI distance for recordings
« Reply #8 on: September 02, 2011, 07:35:48 AM »
Robert, larger objects cars, trucks, trains, and with the depths over 50 feet I find better images with contour on.
We need to get together and run some sonar in you area where the wrecks are.
Do I need to pick up your stuff in NC for you..
Chuck

Offline Roddy

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Re: Optimal SI distance for recordings
« Reply #9 on: September 02, 2011, 08:34:38 AM »
Chuck, Robert; Septerber is here!! Lets all get togather and WK SI work off of Charleston South!

Roddy >:D
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Offline Roddy

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Re: Optimal SI distance for recordings
« Reply #10 on: September 02, 2011, 08:46:09 AM »
Wingnut; In the Charleston SC waters I have gone as far as to use a drop cam,rov and diving on the reefs.

The SCDNR Reefs are not charted well and personal knowledge is a must.

X= 15 tanks just does not work well!!

Roddy
« Last Edit: September 02, 2011, 08:48:54 AM by Roddy »
Scan,Scan and Rescan Roddy

Offline sonar2000

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Re: Optimal SI distance for recordings
« Reply #11 on: September 02, 2011, 09:37:22 AM »
Good idea Roddy, if the outer banks dont get a bridge or roadwe may vacation in SC. 
Robert, lets see what you are doing the first week of Nov...
I may have my towfish by then ;D :P ::) ;)

You guys have better inshore wrecks than we do.. Ours are pretty far out and deeper....


chuck

Offline Roddy

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Re: Optimal SI distance for recordings
« Reply #12 on: September 02, 2011, 09:46:05 AM »
november is good for me! What say ye Robert?    Roddy >:D
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Offline sonar2000

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Re: Optimal SI distance for recordings
« Reply #13 on: September 02, 2011, 11:28:39 AM »
Good idea..maybe we can come up with some settings and some picture for nasdaq.....to help in his set up and runs...
Although it sounds like he is catching on and getting his stuff right... We may learn from him..... :D
chuck
« Last Edit: September 02, 2011, 11:29:55 AM by sonar2000 »

Offline Wingnutt

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Re: Optimal SI distance for recordings
« Reply #14 on: September 03, 2011, 01:50:30 AM »

X= 15 tanks just does not work well!!


Bingo!! You know the deal ;)

Thanks again everyone for the input.  I will try see if makeing a pass with contour mode on first helps.  There really isn't much bottom depth change in the scan area... maybe a 5' delta.  Even if it doesn't, it's not like I can't find structure... I'm just trying to get more detail on my map to make smarter drifts on any given day.

Offline RGecy

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Re: Optimal SI distance for recordings
« Reply #15 on: September 03, 2011, 10:29:43 AM »
Another issue with Contour mode while searching is that you will not see anything that is sticking up in the water column.  If you pass almost directly over something and it has some relief off the bottom, you may not see it or realize what it is.

Robert
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Offline sonar2000

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Re: Optimal SI distance for recordings
« Reply #16 on: September 05, 2011, 12:56:50 PM »
Split screen with DI helps on this...Again, if you are looking for a large object,.... SI with contour on will be fine...
If the target is small then maybe only one side and tight trails..
Chuck

Offline SonarTRX

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Re: Optimal SI distance for recordings
« Reply #17 on: September 05, 2011, 01:58:52 PM »
Hi Wingnutt,

Basic slant range correction (~similar to the Contour mode) of sidescan sonar images becomes tricky for any sonar processing system, when the depth below the transducer vary signifficantly over a short distance (from ping to ping).  The basic assumption of a flat seabed no longer holds true. Sudden changes in depth below the transducer will result in discontinuities ("shear-lines") in the image, unless the depth profile is smoothened out prior to carrying out the slant range correction.

For best contour mode results, try to run your tracks offset from larger objects of interest (or at least do not pass directly above them). In that way, the depth is fairly steady vertically below the transducer, and the assumed slant-range geometry (triangle) undergo less changes from ping to ping(, resulting in fewer "shear-lines" & distortions of the object.)


Tore

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« Last Edit: September 05, 2011, 02:01:52 PM by SonarTRX »

Offline Wingnutt

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Re: Optimal SI distance for recordings
« Reply #18 on: September 07, 2011, 09:58:01 AM »
Hi Wingnutt,

Basic slant range correction (~similar to the Contour mode) of sidescan sonar images becomes tricky for any sonar processing system, when the depth below the transducer vary signifficantly over a short distance (from ping to ping).  The basic assumption of a flat seabed no longer holds true. Sudden changes in depth below the transducer will result in discontinuities ("shear-lines") in the image, unless the depth profile is smoothened out prior to carrying out the slant range correction.

For best contour mode results, try to run your tracks offset from larger objects of interest (or at least do not pass directly above them). In that way, the depth is fairly steady vertically below the transducer, and the assumed slant-range geometry (triangle) undergo less changes from ping to ping(, resulting in fewer "shear-lines" & distortions of the object.)


Tore

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Damn... and I thought it was because the flux capacitor wasn't getting 1.21 gigawatts. ???

Just kidding, I actually do understand what you're saying.

On a different note, I think I read a post where there was a trial version of your software available.  Is that still available and if so how long is it active for (I won't have any recording to load for a couple of weeks)?  I'm thinking it might be easier to look at the entire reef rather than a small section of the recording.

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Re: Optimal SI distance for recordings
« Reply #19 on: September 07, 2011, 11:00:01 AM »
Hi Wingnutt,

...Yes, I realize that the flux capacitor is usually the problem, but...   :)

I just sent you a PM regarding a trial license for SonarTRX-SI.


Tore

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Offline sonar2000

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Re: Optimal SI distance for recordings
« Reply #20 on: September 07, 2011, 01:00:34 PM »
I thought it was the Quantum Flux Capacitor or the Berillum Sphere..
I get so confused with the techinical terms..
 ::).. :P

chuck


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