What Lies Beneath Angkor? Archaeologist Tries to Find Out Using Radar
Till Sonnemann’s work is not so much about groundbreaking discoveries, it’s more about non-destructive verification of archeological theories.
For the past three years, Mr Sonnemann, a PhD University of Sydney student working with the Greater Angkor project, has used ground penetrating radar on various parts of the Angkor complex in Siem Reap to confirm experts’ guesses about what lies buried beneath the monuments of the Angkorian empire.
So far, his radar has turned up four water outlets and various stone features such as tower bases of long vanished temples.
“The opening was about 20 meters wide,” he said of the irrigation outlets he recently discovered, adding the find is significant because it wasn’t known how the water of the Angkor citadel left the Baray Reservoir.
One of the theories was that the water simply diffused through the earthen banks of the Baray.
“Now we know water was taken in and out. But for irrigation or religious or another purpose, it’s still unknown,” Mr Sonnemann said.
Ground penetrating radar, or GPR, is the process that finds and determines the distance of hidden objects by sending radio waves into the ground then measuring the time it takes for the radio waves to reflect off another, buried surface, Mr Sonnemann said.
GPR’s strength are that it is non-intrusive and it can detect buried features and even find objects buried under other objects even before any excavation work is carried out.
“Researchers need to know where these features are before they excavate,” Mr Sonnemann said.
GPR has its limitations, too.
The areas of study need to be dry, relatively clear of obstructions and also do not contain a lot of sediments, Mr Sonnemann said. GPR also cannot tell the age of buried objects.
So far, Mr Sonnemann said he has covered 8 hectares of the complex.
“In comparison to the whole complex that is a tiny bit,” he said, adding he is still working at the site focusing on the Angkorian water management system.
GPR was first employed at Angkor 10 years ago but has been sparsely used because the focus of Angkor research has been on monuments, which the GPR is not ideal for, and because the soils of Angkor also do not yield the strongest results from the equipment, said Dan Penny, director of Greater Angkor, an international research program based in Sydney and is focused on Cambodia’s Angkor period.
GPR is also expensive, and it requires an operator who can process the data, Mr Penny said, noting that Angkor includes many “ancient cultural features” such as house and old temple mounds and canals but a systematic excavation of the entire area is impossible so that is why GPR is useful.
“It is an important tool because it’s non-intrusive or destructive and it brings a series of useful data,” said Christophe Pottier, the outgoing director of Ecole Francaise d’Extreme Orient.
Mr Pottier added that although GPR was first used at Angkor a decade ago, its use has been on small-scale projects and even his organization is still testing the tool in the field.
“[Mr Sonnemann] is going to try to go as far as he can to show the usefulness of GPR,” he added.