Computer Analysis
Ground Penetrating Radar
Farmer Cemetery
Lake Russell Wildlife Management Area
November 5, 2004
Software: GPS-Slice from the Geophysical Archaeometry Laboratory
as written by Dean Goodman
For more information about this software, go to www.gpr-survey.com or click here on GPR-SLiceThis review is written by Jim Winsness based on the expert advice of Kent Schneider, Regional Archeologist for the United States Forest Service, Atlanta Georgia.
The data collected by the Ground Penetrating Radar consists of files for each path that the unit travels across the grid. At each meter distance, the operator presses a button that defines the distance traveled and the reflected signal is recorded. This data, for one path is shown plotted below:
The unit is recording the difference in electrical conductivity of the sub surface and it is easy to note on the right half of the image, distinct differences. These differences most probably are graves.
What is so special is the use of software GPS-Slice from the Geophysical Archaeometry Laboratory as written by Dean Goodman. This software takes the individual data files, each representing a path across the grid, and allows us to see them all as 3-models!
Lets take a look!
First, lets look at the surface of the whole grid:
Each of the dark areas are possibilities of graves. The colored areas may be surface rocks or areas where we just lifted the radar momentarily. We will go back to each of the areas now to find out what the colors mean!
Lets look deeper now into that cube!
The above image is at a depth of 174.6 cm and look at the right end where several anomalies (graves?) seem to appear. Look back at the first image on this page of the vertical slice as it is precisely the same line!
Lets look at the cube again but slice off the end this time instead of the top:
At the end, you can see the pattern of the original gray cross section, now in color, and showing those same anomalies!
But lets look at horizontal sections of all those gray vertical slices.
What you are seeing above is a cross section, horizontal, at a depth of 118.5 - 134.9 cm. Note again, the 'anomalies' at the right end!
Lets look higher:
The horizontal section shown above is at a depth of 77.5 - 93.9 cm and at this higher depth, the graves at the left, and the one in the middle, are less significant. Is it possible that we have in these areas graves that have not caved in yet? Maybe what we are seeing that is so prevalent in those graves is an open area. We will check that possibility out when we return to the site.
If you think the above images are incredible, you have to realize that they are just single images of what is in fact, an animation package. GPS-Slice allows us to literally peel away from top down, bottom up, or end to end, the horizontal or vertical slices you see above. It is the equivalent of removing one centimeter at a time of earth and photographing what you see. We can speed up, slow down, or stop that animation at any point in the display and use what we are seeing on the computer to direct our activities at the site to analyze each anomaly!
As you can see, the work has just begun. Now we go back to the site with the files and we will correlate what we see with the GPR images with known and unknown grave sites. Where we identify unmarked and unknown graves, we will apply head and foot stones to match the appearance of the surrounding graves.
The value of this project will be determined by just how effective it has been in locating and identifying more graves in this old cemetery.
We will report back as we proceed.