You've probably already heard that a recent investigation into Shakespeare's tomb for a documentary on the UK's Channel 4 revealed that the bard's skull has likely been removed from his grave. What you may not know, however, is exactly how that was determined. We caught up with one of the researchers to find out more about grave-glimpsing with ground-penetrating radar.
First, in case you missed the bard's tale, here's what happened.
A team of researchers led by Staffordshire University archaeologist Kevin Colls and geophysicist Erica Utsi from EMC Radar Consulting was allowed for the first time to scan William Shakespeare's grave in the Holy Trinity Church in the English town of Stratford-upon-Avon. When the scans were conducted, Colls determined that something was wrong with the grave. "We have Shakespeare's burial with an odd disturbance at the head end and we have a story that suggests that at some point in history someone's come in and taken the skull of Shakespeare," he said. "It's very, very convincing to me that his skull isn't at Holy Trinity at all."
The findings of Colls, Utsi and their team were laid out in a Channel 4 documentary called Secret History: Shakespeare's Tomb that aired on March 26.
Utsi told Gizmag that the equipment she used to look beneath the ground of the church to, in effect, see into Shakespeare's tomb was called a GroundVue3, a rapid-response ground-penetrating radar (known as GPR) system. The device beams radio waves through material and broadcasts information back based on what it encounters. That makes it different than machines used in hospitals and, in fact, makes it similar to radar systems used by airports — albeit with shorter wavelengths and more material between the radar and its target.
"It is not an optical technique and, unlike other medical scanners, the surveyor is not presented with a picture of what lies underground," Utsi told us. "Portions of the electromagnetic signals transmitted into the ground are reflected back to the receiver antenna as the signals meet any other material. Two-dimensional data is presented on-screen in real time. Three-dimensional images are usually formed by processing the data into a 3D data block which can then provide a bird's eye view down into the ground, as you scroll through all of the layers."
Utsi said that initial scans indicated that the graves in the church were shallow — not 17 feet (5 m) deep as had been suggested.
Once she knew the depth of the graves, Utsi was able to adjust the equipment for the best resolution. "I used a 1.5GHz antenna pair (transmitter/receiver) to map the area of the graves," she told us. "I also used a 4GHz antenna for the same exercise. The implication of the higher frequencies is that they equal shorter wavelengths which equal better target definition and more accurate measurements of depth."
Utsi says that the 4GHz antennas had been previously used to investigate a shallow grave in Westminster Abbey to look for what she terms "grave goods," objects in the tomb other than the body. "There were no grave goods in Shakespeare's grave and no evidence of metal as you would expect if a coffin had been used."
In addition to helping researchers peer into graves, Utsi said that GPR has many other uses.
"Its biggest single use on a day-to-day basis is the detection of subsurface pipes and cables in advance of construction and digging, but there are plenty of other applications from security to glaciology." She also suggests that anyone with an interest in learning more about GPR visit the European GPR Association website.
The documentary detailing Colls and Utsi's find is available to watch online.