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Underwater archeology - help me brainstorm a solution to this vexing problem

alexd

Administrator
Staff member
I have this underwater site I am treasure hunting. It is a sand lake bed in chest deep water. I need to scan every square inch of this lake bed with my detector because artifacts and treasure are there to find. I am scanning the lake bed with a coil that is 6" in diameter. What this means is I have to 'paint' the entire lake bed in the area with the 6" wide coil and, ideally, not miss any spots.

  1. There are no underwater landmarks at the site.
  2. Visibility in the water is not that great. Sometimes I can see the bottom, sometimes not (depends on winds and wave action).
  3. When I start digging up a promising signal, I stir up sediments that can also cloud the water.
  4. There is a gentle current and sometimes strong wave action that obliterates any footprints or holes previously made.
  5. My detector has a built in GPS that I can use to put pins into Google satellite maps, but GPS accuracy is only abut 3 meters, which is not good enough. .

Last year, I dropped 2 floats in the water and tried to walk between them in straight lines to grid off the area. Then I would move the floats to cover the next area over. It worked, sort of, but I probably missed large areas. I was using a larger coil diameter (12") which allowed me to cover area faster, but was not as accurate as the smaller one I want to use this year.

Anyway. My brain storming question is... How can I temporarily mark guides on this area so I can cover every inch of it?
 

agentRC4

TRIBE Member
I would go and get lank marking flags that are 6' high (kinda like a flag on a golf course). You can put stab them into the lake bed and mark your territory and the flag will be above water and won't move or float away (I think)
 
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lucky1

TRIBE Member
bring a couple cement blocks and put them in the water to attach a marker to. This is the cottage trick for marking rocks or logs so boats don't hit them. :)
 

alexd

Administrator
Staff member
The golf flag idea would not work because if the wind picks the waves can get quite large (.75 meters) and wash them away.

As a kid I remember watching a National Geographic special where divers were at an underwater site of an old sunken ship and they were using underwater mini dredges to suck sand way from the ribs of the vessel. On the debris field around it they had overlaid some kind of weighted white plastic grid with 1 metre squares. They used this grid to go after the small stuff in each square and transpose where the objects were found onto a paper map afterwards so they could see at a glance where more finds were made.

I am thinking even a small plastic grid 4 x 1 meter squares might work. I could paint it fluorescent yellow for visibility and work each square, the move the whole thing over to the adjacent spot.

Maybe I should email National Geographic and see if they have any tips....
 

alexd

Administrator
Staff member

That is the answer. Something laid on the lake bed itself instead of bobbing on the surface would give me more accuracy. What to make it out of though? It also has to break down easy for transport on my bike.... Small diameter ABS electrical conduit? I wonder if that stuff floats?
 

glych t.anomaly

TRIBE Member
what about tent poles? the ones that pop out and expand and have string inside?

thin metal poles that easily snap into a grid and break down would be ideal ;)

im sure you could even craft your own, the poles dont have to fit into eachotehr, just for the grin adn then break down into a easily tied up bundle.
 
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agentRC4

TRIBE Member
The golf flag idea would not work because if the wind picks the waves can get quite large (.75 meters) and wash them away.

As a kid I remember watching a National Geographic special where divers were at an underwater site of an old sunken ship and they were using underwater mini dredges to suck sand way from the ribs of the vessel. On the debris field around it they had overlaid some kind of weighted white plastic grid with 1 metre squares. They used this grid to go after the small stuff in each square and transpose where the objects were found onto a paper map afterwards so they could see at a glance where more finds were made.

I am thinking even a small plastic grid 4 x 1 meter squares might work. I could paint it fluorescent yellow for visibility and work each square, the move the whole thing over to the adjacent spot.

Maybe I should email National Geographic and see if they have any tips....
if you could make a clear plastic grid you could pop in GLOW sticks so the grid glows underwater!
 

sk8

TRIBE Member
I usually make survey grids out of PVC pipe because it's light to carry and reassembles easily. I think it would work for underwater, but as some types of the pipe float, a solution might be to fill the structure with water before completing the assembly - that way it will sit on the bottom.
 

Sal De Ban

TRIBE Member
what about some sort of fine-GPS technology? - there has to be something more accurate than 3-metres. or a device that measures distance via sonar?
 
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alexd

Administrator
Staff member


I just found an entire wikkipedia page devoted to underwater searching! baconpanbaconpanbaconpan

Underwater searches - Wikipedia, the free encyclopedia

It is more about search patterns than anything, and is quite comprehensive, so I will see if it can offer any solutions. In the meantime, I have a small piece of that white ABS conduit in the basement, I will see if it floats.
 

alexd

Administrator
Staff member
what about some sort of fine-GPS technology? - there has to be something more accurate than 3-metres. or a device that measures distance via sonar?

My detector has a pretty high end GPS built in, that allows me to set points of various types - findpoints (when you find and recover a target) and waypoints (to get bearings). The problem is, the control box on the detector can't be underwater because the water blocks the GPS satellite signals. Much of this site is just too deep so the control box is submerged.

Also, as I said, the accuracy of non-military grade GPS is not fine enough to mark this site.
 
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coleridge

TRIBE Member
How big of an area do you need to do?

You could buy some orange plastic snow fence from home depot and cut out of it the grid size you want. At each point where you want to secure it to the bottom of the lake you could leave one of the small grid holes and then put stakes through those holes to secure it.
 

glych t.anomaly

TRIBE Member
interesting idea ! ^^^

does that fencing float? and wouldnt you need to cut out teh area that is inside the border of the grid? so you can did and shit easily without having to lift up the whole piece?
 

coleridge

TRIBE Member
Yes you'd cut out bigger holes in the fence to make it the grid size you need.

There are other plastic fence options that might be cheaper. Stuff that has a larger grid and less plastic. But snow fence isn't that expensive and the bright orange would make it stand out.

Yes it would float but it could be secured to the bottom using long tent pegs.

You'd only need two strips of the fence. You'd lay down your first row and then your second right beside it. As you finish searching the first row, you pull up the first strip of fence and lay it down on the other side of the second row. By leap frogging your way along like this you'll be sure to cover the whole area.
 
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