Ground-Penetrating Radar

I did not use it personally but on an historic cemetery survey here. I followed the someone who used it to find unmarked graves.
We pin flagged his spots and then surveyed the locations.
He had credentials. He had done a lot of civil war sites in the South. etc.
We were lucky that we got the locations tied quickly because soon after the Beevis and Butthead personnel of the landscaping company that maintained the cemetery grounds came and destroyed 90% of the pin flags.

A company I worked for had a unit about 10 years ago that we used to locate utilities. The idea was you get a blip on the radar, then dig it up to see what it is. You can't really tell what's there from the GPR.

I have NOT used one myself, but I did have a Boone County, IN, surveyor tell me about one they have. He said it is not much good for finding stone corners when they are standing upright, but if they got knocked over in the course of being buried they show up pretty good.

I am no technical expert here, but I wonder if it may be because of the angle of reflectivity. When the stone is upright very little surface is "square" to the signal and as a result it gets deflected off to the side. When it's laid over, there is surface to reflect the signal back. Sort of like the idea behind stealth airplanes. So, if this theory is correct, it may depend on the angle of the reflective surface.

The most significant performance limitation of GPR is in high-conductivity materials such as clay soils and soils that are salt contaminated. Performance is also limited by signal scattering in heterogeneous conditions (e.g. rocky soils).
Other disadvantages of currently available GPR systems include:

Interpretation of radargrams is generally non-intuitive to the novice.

Considerable expertise is necessary to effectively design, conduct, and interpret GPR surveys.

Relatively high energy consumption can be problematic for extensive field surveys.

I've heard that GPR will only go 1-3cm in very high clay soils so this would be a concern in Lawton.

Deral

Frank,

I had a chance to play with a unit on an asphalt roadway. I tagged along with the operator and watched the screen intently as he educated me on what to look for. As posted above, stones in an upright position are the hardest to discern. Items like walls the easiest. We were looking for a corner that may have been set around 1680±. We were able to identify a few suspicious points and when the road is resurfaced, I will stake out those spots and with the aid of a backhoe, perform a serious search. The road was supposed to have been reworked last year but with the budget the way it is the project is on hold.

Jim Vianna

i used it on a sunken roadway at Mammoth Cave, ky in 1996, spotted a collapse 600 ft below the surface--designed a land bridge using 3m corrogated interlocking panels filling in between with moist sand-- constructed a 800 ft bridge- would hold 3 busses and 3 fire trucks-- will outlast the park i think---tdd

600 feet below the surface??

> i used it on a sunken roadway at Mammoth Cave, ky in 1996, spotted a collapse 600 ft below the surface--designed a land bridge using 3m corrogated interlocking panels filling in between with moist sand-- constructed a 800 ft bridge- would hold 3 busses and 3 fire trucks-- will outlast the park i think---tdd

You forgot to add ...

"AND THEN WE PACKED UP FOR LUNCH".

We used it once to see if there was a body burried under a home addition that a suspect added on the same time a person went missing. Cut a big hole in the slab, shoveled for several hours and found a burried tree stump. Oops

Frank,

I witnessed a demo failure here in Baton Rouge in the middle 1970s. I was not impressed in its capabilities for south Louisiana. Maybe the X-band stuff is better now ...

Thanks, Cliff. I think I am going to try to get a demo. It is amazing to me how hard it is to get people to demo GPR. They want to rent it out and credit 50% if you like it and decide to purchase. Arghhh.

I am a geophysicist and have used GPR for years. During my field work I often encounter surveyors. In these occasions I put geophysical anomalies I found (underground utilities and underground storage tanks, etc) into base map supplied by the surveyors. Although we use GPS and total stations, too, you guys always do better jobs in surveying.

What do you want to use GPR for?

Several things:

Locating graves
Locating underground pipes and tanks
Looking for layers and house post holes in Indian mounds
Locating stumps below the surface

Interesting. I would recommend a cart-mounted GPR with antenna frequency around 250MHz to 400MHz.

I have been involved with surveys that have used GPR, although never for finding property corners.

For one project, we hired a subcontractor to locate all the underground utilities in a toll plaza for the Whitestone Bridge.
The operator laid out a grid and ran his machine over each section. He was able to find and identify water mains and electrical ducts. We provided the grid using our H & V control datums, so that he could provide a map which we integrated into our surface topo.

The same contractor was used to determine the size and depth of a series of buried tanks in several old refueling centers. The data turned out to be pretty accurate.

We also used a GPR system to establish pavement depths along the Long Island Expressway. After a test section on a portion of the highway that was already being reconstructed (so we knew the depths of each asphalt lift, concrete base and sub-base), the unit was attached to a small trailer and we pulled it along the highway at 55 MPH. We used the six or seven bridge overpasses as waypoints, and thus determined the depth for the center of each of six lanes by making six passes along the highway. We did about five miles of the expressway in less than a day, and just moved along with traffic each time.

The output in this case was a graph, which showed the different densities of the area being scanned, to a depth of about five feet (we were only interested in the pavement and sub-base material anyway). We input the bridge waypoints by clicking a mouse on the laptop it was attached to. Again, this was handled by a subcontractor, with yours truly inputting the waypoints riding in the back of the pickup.

The system worked pretty well and it even showed us the pavement joints and could even identify patched areas where the depth or the material was different, so we had additional control to determine where we were. Where drainage pipes crossed the lane, we could see the image if it wasn't too deep. This enabled the State DOT to forgo closing lanes to take cores.
I'm guessing the sensitivity can be tuned up or down for greater depth perception.