Hello,
I'm part of a long term biological monitoring project, and we need a method of finding exact geographic locations 5-10 years in the future. We are working in all types of land tenures (crown, privately owned, oil/gas leases...forested, cutblocks, agriculture...) and often can't leave any sort of above ground marking. We are also working in areas with heavy canopy cover, so a differential GPS is relatively useless. At most sites, we currently bury an 8 inch iron spike, in hope of going back with a metal detector and relocating those nails. We've been pretty unsuccessful so far.
Does anyone have any suggestions for a method of finding this locations, that technicians could use without a great deal of training?
We use simple handheld Garmin GPS units, with accuracies usually within ~ 10m. We can get back to the general area, but we need to be able to find the exact location.
Thanks for your help.
When you place a buried monument, record the distance and approximate direction to at least two objects (more is better) such that taping back will intersect (nearly right angles if possible) at the monument. If you can find semi-permanent features such as gate posts, unique trees, or stream beds within a few hundred feet and at a decent angle from each other, this should get you close enough to use the metal detector.
Are you allowed to nail "shiner" washers to trees? When those are used on trees or fence posts, it is possible to measure very accurately back to the monument.
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If you are using iron spikes to monument the points, then you MUST use a magnetic locator such as sold by surveyors' supply companies, and not a treasure hunter, in order to have sufficient sensitivity.
If you are limited by budget to a treasure hunter type of detector, then bury aluminum pie plates, not iron. Each detector is optimized for its target.
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Under canopy, it would be essential to let the Garmin GPS average the waypoint for several minutes, or as long as practical. When you return, get in the vicinity, take a new averaged waypoint, and note the distance and direction to the old one.
This practice should get you close enough to find the local features you noted when placing the monument. "37 feet north of the double-trunk tree and 42 feet east of the only maple in the area"
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Hope these ideas help.
Since you mention your work is in heavy canopy, do these technicians know their trees?
I'd be sure they can sketch properly, orient north correctly, and give tie distances to the nearest foot on the face of nearby significant trees (at DBH). Of course, the tie distance will change over time slightly, and you're only trying to find a spike marking your site. The nearest foot should be plenty sufficient. You could also bury an additional 8" spike at the base of the tie trees so your techs knew they found the right ties.
Best to hire a land surveyor in your area of Canada (it sounds like) to use proper techniques along with survey grade GNSS and Optical Instruments to locate points more accurately. Have them provide you with a report along with physical ties.
Lee Green
Thank you very much for the response. It's very helpful.
As a follow up, do you know if magnetic locator effectiveness would be impeded by the water in saturated soils?
To add to my original post, one of our main issues is that we're are often working in areas that are susceptible to significant change (logging, flooded wetlands...). Yes, we will often be able to use shiners, and our technicians also know their trees well. When applicable, we will certainly use the practice of measuring distances/bearing to permanent features, but we may not always have that option.
Yes, that would be ideal, but it's unfortunately not feasible.
I do not have experience with metal detectors, but if
you are going to use a survey grade magnetic locator
then, along with setting the reference points in trees, etc.
I would set a magnet alongside or under each spike.
The magnet will greatly increase the range of
detection of the locator. If you can spend the
money, Bernsten sells some that are encased in plastic.
"....in hope of going back with a metal detector and relocating those nails. We've been pretty unsuccessful so far."
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I don't know if you're using one of those precious metal type detectors or a "real" magnetic Locator such as these
Schonstedt Magnetic field detector
That could make a huge difference for you! Also, the suggestions to create bearing trees is an easy way to get real close to your point!
Dtp
Get some tree paint, yellow or red.
Set your spike, generous use of flo pink flagging will help find it later.
With Compass and Tape measure and take notes on at least 3 nearby trees, note size and species. Put a big spot of tree paint on the tree facing the spike, even better blaze the tree with an axe then paint the blaze but I wouldn't do this without property owner permission. You can also do this with fence posts and utility poles (but maybe be careful about painting those, owners may not like it).
You could get some yellow metal bearing tree tags and nail those to the face of the nearby trees. Leave the nails out at least an inch to allow for growth.
http://www.benmeadows.com/aluminum-location-posters-and-bearing-tree-posters_36814211/
The way the Foresters mark their CFI (Certified Forest Inventory) plots is this:
They use a plastic stake.
On the nearest road at the parking spot they paint up a tree "T.O.P." with tree paint and sometimes a metal tag. T.O.P. stands for take off point. Then they have notes on direction and distance to the plastic stake (sometimes a fair distance). You just follow the bearing and distance with compass and pace until you find the stake. Sometimes they have an obvious flagged trail, flags every 5' or so.
Ummm? Is this a stealth project.
