Understanding the process and technology of detecting unmarked graves has become a focus following the announcement that preliminary findings from a survey of the grounds of a former residential school in Kamloops, B.C., indicate that the remains of 215 children could be buried at the site, CBC reports. That determination was made by a specialist who used ground-penetrating radar (GPR), a geophysical survey method to examine the site. The technology is used on sites to determine the presence of underground conduits, water pipes and gas and sewer lines. But it also can be used to scan historic cemeteries and unmarked graves. Survey teams use ground-penetrating radar devices to roll across the surface of the earth. GPR is much like a medical ultrasound, but instead, high-frequency radio waves penetrate the ground to form an image of what may be below, according to B.C.-based GeoScan Subsurface Surveys. The device, a box about 25 centimetres wide with wheels, is pushed or pulled by a technician who scans the land in lines. The device includes a radar-transmitting antenna that sends high-frequency waves into the ground that will bounce back to the receiver if they hit anything that is different from the medium of the soil. A computer can reassemble all of the lines and look at the results in three dimensions. The technology cannot pick up organic matter, meaning it will not be able to determine whether skeletal remains lie below.