Seeing Beneath the Surface: How Ground-Penetrating Radar Works

Ground-penetrating radar (GPR), a technology developed for gas and oil exploration, allows archaeologists to identify the possible presence of subsurface features without digging. In the photo above, an antenna transmitting impulses and receiving echoes is dragged over the site by author Yonathan Mizrachi (right) and an assistant. It sends high-frequency electromagnetic impulses into the ground. When the signal hits the interface between two subsurface layers, such as the surface of a buried wall or a cavity beneath the ground, part of the signal is reflected back. The rest continues still deeper to be reflected by other layers or objects (see diagram below).