GPR. If there were magical letters to cemetery folks GPR is it. Or is it? A lot of folks have seen a typical GPR unit in use. The usual model resembles a lawn mower with a video screen for cemetery uses.
Just as one doesn’t need to know how a car engine works to get a drivers license, the more one learns about a car the more you know when something is wrong or needs attention.
GPR is similar in this fashion. You don’t have to have a degree in geophysics but the more you understand GPR’s uses and limitations, the better information and decisions will be had.
FACT! - GPR IS NOT AN X-RAY MACHINE. Do not expect to use GPR and see bones in a coffin or in the ground.
At its basic level GPR emits a burst/pulse on microwave energy downward. What comes back is/are reflection/s. It is these reflections that the degree or extra training in geophysics comes in handy.
The above picture is what you first see on a typical GPR screen. It displays the depth of the wave, area covered in length. The operator has the option to mark the return waves with arrows. The reflected waves suggest to the user that there might be something of interest or not.
FACT! - IT REALLY HELPS TO KNOW THE SOIL TYPE, RECENT WEATHER (RAIN) AND THE REASON YOU’RE SCANNING THAT AREA.
Soil types affect density which affects reflectance. Recent rain fall or high water table affect reflectance.
Lastly, you have a good reason to believe that you are in the right search area.
I have used GSSI GPR equipment, an industry leader in GPR from Nashua, NH. I have GPR’d veteran graves at the State’s four veteran cemeteries. I can tell you once you start to understand the waveforms it becomes a good tool to find the edge of existing coffin/casket. As long as you understand the soil type, water levels, recent fertilizer/pesticide applications and are fairly certain that there is reason to believe something is done there are the expected depth. See? Simple.
At this point the discussion will become very technical. Let’s end with the understanding and expectation that GPR is a good tool on the belt that may or may not provide the evidence you seek.
by Glenn Roberts