Lasers Used to Map Ancient Water at Angkor, Provides Clues on Population

Jonathan Cox / Khmer Times No Comments Share:

The secret to the number of people who actually lived in the city center of Angkor Thom may lie not in the number of buildings but in the number and size of its ponds, according to a new archaeological study released last week. Until now, most research about the Angkor city center has focused on the grand temples, while the mundane details of everyday life – such as where the city’s residents got their water – have been ignored. This new study, published last week in Archaeological Prospection, finds secrets in these mundane details.

Since ponds were used as the water supply by the city’s residents, the team of researchers – led by Kasper Hanus of Adam Mickiewicz University in Poland and Damian Evans of the University of Sydney – hypothesized that the number of ponds could provide a clue to the number of residents. “Small-scale ponds were a vital part of the water management system of Angkor,” the study said.

Counting the number of ponds that existed in the 14th century can be a difficult task, but using detailed maps created with airborne laser scanning, and making clever use of a depth mapping algorithm, the archaeological team was able to estimate the number of ponds in the area. 

The study yielded some surprising results, showing that the actual population of the area may have been much lower than previously thought.

The research team’s population estimates were based partly on reports recorded by a Chinese envoy to Angkor named Zhou Daguan in the late 13th century. Daguan said that groups of between one and three families shared a single water source. With this vital piece of information, the team decided that mapping water sources in the Angkor city could give a clue to the number of its inhabitants.

Mr. Hanus and Mr. Mickiewicz used maps of the Angkor urban complex created with airborne laser scanning (or LiDAR) by the Khmer Archaeology LiDAR Consortium in 2012.

LiDAR scans can collect data about the topography of a landscape, even through dense tree cover, by bouncing lasers off the ground and recording how long it takes for each to reflect back into the sensor. Using the billions of data points this process gathers, it’s easy to generate detailed maps of an area. While archaeologists once mapped terrain on foot, with a large amount of guesswork, LiDAR maps like this have provided a new level of precision.

Using an algorithm to detect the location of ponds in the city center, the researchers mapped 1,651 ponds within the walls of Angkor Thom, the city center, and a total 3,170 ponds in the greater area. 

Given Zhou Daguan’s reports from the 13th century, they estimated that the actual population in Angkor Thom may have been around 30,000 – much lower than the current estimates of 90,000. Further research is needed, though, before any conclusions can be drawn about how many people actually lived in Angkor.

“Now that we can clearly identify the number and areas of ponds…the density of residents per hectare remains one of the few critically important pieces of the demographic puzzle that are missing,” the study said.

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