Archaeologists use advanced sensing technologies to map excavations
Archaeologists use advanced sensing technologies such as airborne laser scanning (LiDAR) technology and ground-penetrating radar to map targeted excavation sites.
“The main activity of archaeologists is working out where to excavate, in order to try and find a feature, and we’re very good at it,” said the University of Sydney’s Professor Roland Fletcher, “It’s quite a skill because you have to take into account the nature of the ground surface and then anything you know about where materials are, it’s quite an art.”
Professor Roland Fletcher (Theoretical and World Archaeology) and Dr Damian Evans from the University of Sydney, a member university of the NSSN, lead the Greater Angkor Project in Cambodia. Their team of researchers use remote sensing technology in mapping Angkor, which according to UNESCO, is one of the largest archaeological sites in operation in the world.
“We have used aerial and space platforms to identify the plan of the urban area which is huge, an absolutely enormous place, and we have used ground penetration radar to get into identifying where buried channels are located and actually found the temple which had been seen [before] that nobody had understood what it was for about 40 years.”
In 2012, Professor Fletcher and his colleagues at the Greater Angkor Project used LiDAR to map the main central area of the city of Angkor (approximately 300 km2).
“The reason for using LiDAR is that much of that area [Angkor] is either densely covered with forest or very scrappy vegetation. What you can do with the LiDAR is that you can remove all the vegetation from the image,” said Professor Fletcher.
LiDAR is a remote sensing technology that uses the pulse from a laser to collect measurements. A LiDAR system measures the time it takes for the laser beam to hit an object or surface and reflect to the scanner. The distance is calculated using the velocity of light (299,792,458 metres per second). LiDAR systems can fire around 1,000,000 pulses per second. Each of the returns can then be processed into a 3D visualisation known as a “point cloud”.
“What LiDAR gives you is a 3D image from the top of the vegetation down to the ground,” said Professor Fletcher, “so you can actually get what is called a ‘bare earth image’ uninterrupted by any vegetation, which is very useful.”
LiDAR can also reveal insights about the changes in the climate that caused damage to the environment. For instance, the 3D-processed images produced as a result of LiDAR measuring enable archaeologist to see the damage caused by severe flooding.
“We can actually see erosion damage. Erosion caused by water has very distinct physical forms. We can also see in the middle of the city [Angkor] where the erosion operated at three different levels. First of all, gouged out high, and then further down, and then right down the bottom. So it relates particularly to seeing the effects of a change in climate,” said Professor Fletcher.
Before LiDAR existed, excavators used surveying equipment and conducted their studies on the field, which in the context of a forest is difficult and dangerous.
Archaeology, like many other disciplines, can benefit from developments in the field of quantum sensing, which enable the development of gravity sensors that can reveal what is beneath the surface of the ground.
“What I’m particularly interested in is to get a high resolution, three-dimensional subsurface image, preferably down 20 to 40 meters,” said Professor Fletcher. “That would allow you to see in three dimensions everything that is below the ground surface. So that you would no longer have to excavate first-of-all, to find out what is there. You would be able to see what is there and then research would be much more efficient and much more economical.”
For several centuries (9th to the 15th) Angkor had been the centre of the Khmer Kingdom. With impressive monuments, several ancient urban plans and large water reservoirs, the site is a unique concentration of features testifying to an exceptional civilisation. One of the monuments is the famous Temple of Angkor Wat.
“To give you some idea of how big the whole enclosure area of Angkor Wat is, it’s the same size as the main campus of the University of Sydney. It’s big. It’s very big,” said Professor Fletcher “The temple would stretch from Fisher Library down to the Wallace lecture theatre.”
Access to cutting-edge research equipment can be difficult to arrange without university partners. With over 50 centres of excellence, collaborative research centres and industrial training centres spread across the NSW Smart Sensing Network, access to world-class smart sensing technology and expertise is readily available.