Archaeological Imaging at Uncle Tom’s Cabin

Using ground penetrating radar to survey for unmarked graves.

Uncle Tom’s Cabin is a heritage site operated by the Ontario Heritage Trust.  It takes its name from Harriet Beecher Stowe’s novel.  The cabin once belonged to Reverend Josiah Henson, on whose life Beecher Stowe loosely based the events of her novel.  It stands on land that was once the Dawn Settlement – a self-sufficient Black community in part founded and financed by Henson that was intended to give Blacks who escaped to Canada a new life with opportunities to prosper. You can learn more on the OHT’s site.

Part of the settlement included the Henson Family cemetery, which includes a memorial stone to Josiah Henson, and which is still in use for family members. As part of its site management, the OHT wanted to investigate the possibility that there were unmarked graves on the cemetery lot.  In 2011, they approached the University of Western Ontario to come and survey the lot with the ground penetrating radar (GPR) equipment acquired for the Sustainable Archaeology: Western facility. This was a follow up to a survey performed in 2008 by UWO using a different kind of geophysical imaging technique called Magnetic Gradiometry.  This survey, conducted through a partnership between the OHT and Timmins Martelle Heritage Consultants (TMHC), was inconclusive, and it was hoped that the radar would prove more effective.

GPR in Use – courtesy of Ed Eastaugh, UWO Anthropology

GPR works by sending radar waves from an antenna into the ground.  These reflect off of buried objects, but also changes in the soil distribution. This can detect areas that have been disturbed – for example by digging a grave.  These reflections are captured by software, which indicates areas where the waves have reflected.  In order to cover an area, the machine is wheeled in parallel lines inside a predetermined grid. Trained operators can interpret these data and images and get a sense of what the reflections mean throughout the survey area.

Composite map of radar reflections – Red indicates probable disturbances.

In the above image, we can see the original radar image superimposed on a map of the cemetery. Below, we see the ‘translation’ of that radar image into the location of unmarked graves.  The survey uncovered upwards of 300 unmarked graves on the site, and one clear area in the north that could be used for future internments.

Graphical representation of the likely location and density of graves at the Henson Family Cemetery