Sometimes the use of GPR can be absolutely hilarious, consider this case in point. Several years ago IBM had a problem with a set of pipes carrying hydrogen gas from an above ground storage tank across the parking lot of their plant in East Fishkill, New York. The hydrogen is used in making computer chips. IBM had issued a contract for some archaeological excavation work to be performed in their parking lot. The contractor was given blueprints of the lot that showed two sets of pipes in different places after they had been told there were only one set of pipes.
Needless to say with the information supplied the contractor wasn’t sure of exactly where the pipes were. He became especially nervous after some of the officials at IBM had informed him that if he broke either of the pipes it would cost him $8 million a minute. He had heard about Ground Penetrating Radar, so he found out who manufactured the units, and put in a phone call to the manufacturer, Geophysical Survey Systems, Inc. of Salem, New Hampshire who had a policy of giving GPR jobs to the nearest owner of one of their units to the job site.
Presently we received a phone call from the contractor explaining his problem. We showed up bright and early the next morning with our unit, set the instrument up, selected the proper antenna for the job, and went trolling for the errant pipes. The antenna we selected looks for the entire world like a power lawnmower with an extension cord leading back to the unit in the van. After we had been going back and forth in the parking lot for a while we attracted some attention from the denizens inside the plant, and out came some junior executive who asked what we were doing.
We explained what we were looking for, and how the GPR unit worked, and with that he went back into the plant. About twenty minutes passed when several more executives came out from the plant including the general manager who invited us, and our GPR unit, to come back into the plant. We marked off with a can of spray paint where we stopped with the GPR survey, and followed them into the plant. The general manager explained to us they were having the same problem inside the plant with the same set of pipes, and they also having the same problem finding the pipes because they had two sets of prints showing the pipes in different locations.
IBM is one of the most high-tech companies in the world, but their best effort was a janitor with a pair of bent coat hangers dowsing for the pipes. We got an extra job out of the deal where everybody paid us by the hour for our services.
This is how GPR works: It is similar too your kitchen microwave in that it uses a cavity magnetometer to generate the radar micro waves, but the similarity to a microwave oven ends there. The power generated by a GPR unit is roughly 1/20,000 of the power generated by a microwave oven. The beam is not focused, so it is not like a searchlight, but more like a floodlight. GPR does not generate a sharp image like a camera, but rather an image produced by the radar waves acting against the difference in dielectric strength between the earth and any object buried in the ground. This produces an echo that is returned to the GPR unit that converts it to an image on some form of monitor where it can be interpreted by the operator into useful information about subsurface conditions. The readout can be either a digital image on a screen, from an archaeology site sometimes, or a printout from a multichannel oscillograph.
Most GPR units use both systems together because the printout is hard copy that can be stored. The digital copy is also stored in some sort of device that stores memory.
Author Bio John Carter is a geologist that paid his way through college as a commercial helicopter pilot in the NY Metro area. He has had extensive experience as a prospector, and operated an environmental consulting firm specializing in environmental site assessments and is certified by the State of Connecticut as an Environmental Analyst III. In his early life he worked as an experimental machinist on aircraft and electronic parts before receiving his degree as a geologist. Carter also owns the website Gold Mining and Prospecting.
More of John Carter’s Articles
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