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Old 09-05-2008, 09:56 PM   #1
Diver1111
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Default More side-scan-sonar images

Hi All,

I post some new shots I have taken of old things in the lake:

- Empty Pockets off Diamond: Always tough to get a good shot of as it's water-logged wood (not very reflective) and sits at a right angle to the shore sloping downwards-opposite of what I need for a good scan; Best scans are taken at 90 degrees to the target;

- Crude shot of the Lady of Lake in Glendale;

- Log field off Meredith (west side): Adjacent to the old shake factory, now the site of Church Landing; I am guessing these are very old logs that wound up in the lake on their way to the factory on the shore nearby; This area is littered with such logs;

- "Pile Driver barge w-derrick" off Weirs: I am guessing it is made of wood by the lack of reflectivity; I am told it has/had a derrick on board to drive the piles-the pointed object appears to be the derrick, which I think has fallen over off the end of the barge; Derricks are upright when in position;

- Barge w-derrick #2; Clearly something is laying on the lake floor-long, fairly pointed-derrick?

- Barge-heavy metal on deck; Something very hard is creating the white area; I'm guessing it's industrial equipment of some kind; Whatever it is it's pretty big and box-like, clearly metal;

- Sonar vs. Side-Scan-Sonar: Pile driver barge on sonar (fishfinder)/left image and side-scan-sonar/right image together via a split screen; The barge doesn't even show up on the sonar and considering it's supposed to be 90 feet long you would think it might; You can see what appears to be the derrick again, lying on the lake floor to the left of the main deck; The blue area in the image to the right of the green arrow is the water column (surface to lake floor); The white string-like image is actually my marker buoy (the white dot) and line, descending from the surface of the lake down to the deck; The marker buoy looks like it's hanging in the water column somewhere under water, but it's not; I'm surprised I even picked it up on side scan but it does have some metal clips and rings on it that reflected.
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BroadHopper (09-07-2008), chipj29 (09-06-2008), ironhorsetim (09-06-2008), ITD (09-06-2008), Orion (09-06-2008), Rose (09-06-2008), Senter Cove Guy (09-06-2008)
Old 09-06-2008, 06:19 AM   #2
Winni4life
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Default Great Shots

Always wondered what some of these items looked like. Thanks for posting!!!!
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Old 09-06-2008, 08:08 AM   #3
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Thumbs up Fantastic images!!!

Thanks for posting these great images...I prob. will never dive on Winni, so this is the next best thing. If you ever went by diamond Isl. I would love to see the area in and around the military underwater site. Thanks Again loved it!!!
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Old 09-06-2008, 09:14 AM   #4
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Thumbs up very cool

those are some great shots and to think they aren't all that deep. thanks for posting and tell me where I can see more
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Old 09-06-2008, 10:27 AM   #5
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Default Offsets?

Thanks for posting these, they're great! Based on your description of the last item, it appears you need to be offset quite a bit to get these scans. About how far off the wreck do you need to be to get such an image as the last one at 45' deep? Looks like that sonar has pretty good range.
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Old 09-06-2008, 06:52 PM   #6
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Default Nice shots.

Really clear shots Hans. I'll be picking up a dry suit this winter so we can dive deeper next summer. Like to see the barge with equipment up close.
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Old 09-07-2008, 06:42 AM   #7
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Default

I have to say I am very interested in these but I have no idea what I am looking at. Can someone help? Even reading the descriptions doesn't help me. Sorry to be so stupid.
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Old 09-07-2008, 08:19 AM   #8
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Default Answer

Orion:
Distance needed from target will vary by depth and scan range. Range with this unit is up to 480 wide, left and right combined; Distance at the time I took them of the barge was approx. 50 feet, or a 1:1 scale (50 feet of water, 50 feet away); Get too close and the image will split, giving the illusion that part of an object is standing in the water column itself-this can be very misleading to an interpreter unless they were on board the vessel at the time the image was taken;

Tis:
Stupid has no bearing on your question-if you don't know you don't know-that's not stupid at all;
Answers: Empty Pockets was a 1950's-era cabin cruiser (without the cabin anymore) in 55 feet of water off Diamond; The Lady of the Lake is an 1888-era steamship that was to be scuttled in the lake after being stripped but sank prematurely while being towed out-sitting in Glendale about 400 feet out from NH Marine Patrol HQ; Log field off Meredith-a well known sawmill produced shingles (shakes) way way back on the point in Meredith-logs were floated there for production; The Pile Driver barge sits off Weirs Beach-was once used I am told for viewing a large fireworks display in about 1922-when things got going too many people went to one side at once, the barge listed and sank;
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Old 09-07-2008, 06:09 PM   #9
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Default

Diver, what I mean is, I don't know what I am looking at. Some of the "items" seem to be on the left and some on the right. Maybe I need to read your last paragraph a little more carefully. It reminds me of an xray, I have no idea how they see anything. Thanks.
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Old 09-07-2008, 07:40 PM   #10
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Default Notice the headings

Especially on the last four scans, if you look at the headings, which are compass headings (true degrees versus magnetic degrees), there are passes heading 071 degrees, mainly easterly, and 256 degrees, mainly westerly; there is also ones of 068 degrees and 143 degrees, giving different views of the same object. The frames also give you information as to looking to the right or looking to the left and I believe how many degrees of the heading of the boat.

You could almost make a circle, and with the headings (071) and the fact it is a right side scan of 085, keeping the center of the circle as the object, you could then plot the four different passes that Diver made to obtain these scans.

As a former air traffic controller, it does seem to make sense to me, and I hope that Diver will correct me if I am wrong.
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Old 09-07-2008, 09:35 PM   #11
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Default Answers

Hi All,

To clarify-Upthesaukee is correct. The Course (aka Heading) is the direction my boat is traveling.

In the picture referenced-"85" is 85 feet-the scanning distance I chose out from the boat, out 90 degrees from the direction of travel of the boat. A right angle. I can set this up to 240 feet per side. Hence 480 feet total scan if scanning left and right simultaneously. Hardcore commercial units can easily go 1,000 feet or more per side. However to generate larger images on the screen I will often scan one side only, thus reducing the total width of the scan BUT getting larger images on the screen.

If I am trying to locate something or just curious about an area, I will "scan wide" using both sides available to varying distances dictated by water depth. This is how I found the barge. I had an idea of where it was but no specifics, so I scanned two sides at once, made only a few passes and saw an interesting image, then moved my screen cursor (yes we have cursors) over the TOI/target-of-interest and marked it (I can move my cursor over any object, lock on to it and capture it's Lat/Lon. Then it's only a matter of navigating over the object by selecting Go To in my chartplotter-choosing the TOI just captured-and get right on it. Very useful to say the least).

If you look carefully at the green arrow in the image in question, you will see the image of a boat-my boat-just above it. This will tell you where the boat is in relation to the entire image. The green arrow says I am scanning to the right. The boat image is cut in half because I am only scanning to one side. If I was scanning left and right at the same time, the entire boat icon would appear.

Multiple passes by a TOI is Side-scan 101; Images can be badly twisted for a number of reasons-so you need to scan as many times as necessary to develop a feel for what you have. This is why I have several different Courses indicated in the images-different passes.

Hope it helps.
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