I have just packed up my trowel after completing the spring excavations for the Glenbow Town and Quarry Project of the Archaeological Society of Alberta – Calgary Centre. Now is the time for reflection and analysis and this year I have some new types of data to contemplate.
I am often asked by members of the public (usually retired geologists), who hike or cycle past my excavation area in Glenbow Ranch Provincial Park, whether we have done any remote sensing at Glenbow. In essence, remote sensing allows you to see what is below the ground without digging it up first. A simple example is using a metal detector and, yes, we have tried this. Sadly, our site is littered with so many rusty nails from the previously existing buildings, that the scatter of positive readings is too large to be meaningful. However, this year, we were fortunate to have a magnetometer survey done by Lance Evans of Lunate Consulting. This type of geophysical survey measures and maps patterns of magnetism in the soil. The contrast between some areas of the soil against the background of the Earth’s magnetic field can indicate past human activity.
Lance graciously came out to the park and conducted surveys in three different areas that are of interest to us. First, his crew marked an area to sample, such as a 20 by 30 meter rectangle. Then, after calibrating their instrument, they carried it across the rectangle in a pattern of parallel lines. The instrument is very sensitive, therefore they had emptied their pockets of cellphones, keys, and wallets (which contained magnetic bank cards). They even had to refrain from wearing clothes with zippers or metal fastenings in order to avoid contaminating the data. After the survey, the information gathered by the instrument was processed by special computer software and a map indicating the strength of the magnetic variation was produced.
This map, in shades of black, gray and white, was interpreted by Lance to indicate areas of metal concentrations, hearth features, and ground disturbances. There are also a couple areas with strong and unusual readings that beg for further investigation. This is my first experience with magnetometry and I am still learning to understand the splotches of black and white on the maps, but I did get the chance to verify the accuracy of the readings. While digging in one of our trenches, we discovered a concentration of nails. Measuring against the site pegs, we determined that it occurred in just the spot where the map indicated a significant metal deposit.
The project also benefited greatly from the contributions of Rapid3D again this year. Peter Dobson returned to Glenbow with some new tools in his grab-bag of technological wonders. First, he demonstrated how to take a series of photographs which then could be manipulated with computer software to create three-dimensional images of artifacts. Next, he set up a laser mounted on a tripod to scan a landscape feature. The resulting computer image allowed us to see the feature with greater clarity before we excavated it. This technique was similar to the scan in 2015 of our completed excavation of the cobble foundation (see November 2015 — Old Stones and New Views: The Use of Futuristic Technology on an Historic Site). Peter finished off with a new, advanced, extremely expensive, hand-held laser scanner to record another engraved stone we located this spring. The computer image produced showed the texture of the stone surface and its alteration in fine detail.
We are very grateful to Lunate Consulting and Rapid3D for donating their time and technology to help us with our project. Their generosity has allowed us to see our Glenbow archaeological sites in a whole new light.
Read about our summer adventures on our project blog.
This article was originally printed in the BERGEN NEWS and is being reprinted with permission.