Humminbird Side Imaging Forums
Side Imaging Forums => 797c SI => Topic started by: PT on January 31, 2010, 07:22:31 PM
-
I recently shot some sonar of a collapsed wooden wreck in 20 metres (60ft) of seawater. The wreck is encased in a mound of mud and shells and stands 2 metres (6.5ft) above the surrounding seabed. When viewed in Humviewer; is it possible to estimate the amount of hull structure remaining by measuring the sonar image?
Thanks for any help
PT
-
If you use Martin's new Humviewer 44...there is a measuring tool under the "Utilities" button at the top left of the page....
-
Martin's Humviewer is a fantastic tool, but what I am trying to work out is how far the sonar signal will penetrate into the mud, and will there be a reflection from a deck or the inside of the hull. And if so, what should it look like.
PT
-
PT
The mud will absorb the sonar signal, so the bottom picture will appear deeper. The best way to see this is to do to a know area of different bottoms, weed, rocks, sand, stone and mud. record these so you can review them several times.
George
-
PT you ask a very good question. In general sonar on the color screen in the 200 transducer will show the bottom where a hard bottom will be thin and a soft bottom such as mud or sand will appear thicker. Ok this is the first layer of reflected signal and from the display we most of the time see several layers and colors on the 2d. Your question of what if the material under the soft bottom (mud and not very thick) is a hard material. what will be the return on the bottom display. If the mud is not very thick then you will probably see the second layer. Darn these questions. Now you have added another project to my already busy projects this spring. ;D I will see if I can dig some holes and put some thick wood or metal under a known layer of Mud. This should be interesting. Hmmmmmm just how far can we see under the bottom layer and what is the relationship of hard to soft at this point. Thanks. chuck
-
is it possible to estimate the amount of hull structure remaining by measuring the sonar image?
Wooden wrecks and wet wood is allways a problem to find and to see with sonars and sidescans. Old wood contains up to over 90% of water. The signal goes through the wood. The good thing is that its not going back trough the wood so its leaving a shadow behind the wood. IF IT IS POSSIBLE!
Therefore old wood wrecks should be scanned from a long distans, so you could get a longer visibel shadow behind the wreck. So it is the shadow you actualy can see, not the wood it self.
If you want a picture of a wooden wreck, that is laying close to the shor,take the picture from the shallow waters out to the deep water. Drive your boat as close to the shoreline as you can. Then you get longer shadows.
Kimi
-
I talked to a friend of mine who was running sonar in the 90's looking for old airplanes. He indicated that you would be able to see a dark sahdow under mud but that other than length was about all you could tell. The planes were mostly metal frame and composite so he was not too sure of wooden wrecks. He also indicated that the 2d down would or might be the best screen to use. he felt that a lot of under the mud might be overshadowed by side imageing. Hope this helps and if you get any images from your runs please post for us to see. Chuck
-
Is this what you guys are talking about.
Soft mud with hard bottom underneath?
Sorry about the poor image quality, I am just now learning how to adjust my settings. These are default 797 settings.
(http://i803.photobucket.com/albums/yy319/ezdaar/side%20scan/S00014.png)
-
Yes on the 2d display you will see thickness of bottom or softness or hardness. Depends on the bottom but the display will show these features. chuck
-
Apolgies for butting into your post, PT, but I think this may be a picture of one of the 18th century wooden rowing ferries that used to cross Windermere. It's the right size and shape and in the right place and I am presuming that this is buried in the soft bottom silt and the lighter outline is the wood showing up harder than the silt. Certainly more modern wrecks and detritus lay on the silt and not under it. The 'L' shaped item to the left of the zoom is a modern anchor for a floating mooring.
(http://i703.photobucket.com/albums/ww34/IRCKevin/S00075.jpg)