LiDAR – or Light Detection And Ranging – is a form of laser-scanning, initially used in meteorology. Over the past decade or so, archaeologists have begun routinely to use the technology, drawn to its ability to capture extraordinarily accurate, high-resolution, 3D data. It works by using light sensors to measure the distance between the sensor and the target object. This results in a series of ‘dots’ that computer wizardry is able to convert into a 3D mesh.
The principle behind LiDAR is quite simple: light travels very fast – about 300,000km per second, 186,000 miles per second, or 0.3m per nanosecond, and LiDAR measures the time it takes for the light to return to its source. Naturally, the equipment required to measure this has to operate extremely fast, and it is only with advances in modern computing technology that this has become possible.
Archaeologists may use LiDAR on the ground, where it is able to record buildings or monuments in extreme detail. But, as at Angkor, it can also be used from an aircraft (the team used a helicopter), with the sensor recording all that lies on the surface of the ground, whether buildings, vegetation, or the earth itself. Indeed, at Angkor Wat (see CWA 77), LiDAR has, for the first time, allowed the easy and efficient mapping of terrain normally obscured by dense and protected vegetation.
Given the accuracy and speed of data-capture, LiDAR is far more cost-effective than traditional survey methods. It is also non-destructive and chronologically informative. Is this the future of aerial archaeology? Certainly fieldworkers in many parts of the world think so: witness recent LiDAR surveys at Caracol in Belize and, last year, at the pre-Classic Maya settlement at El Mirador, Guatemala, or the pioneering survey of the grounds of the colonial Wye Hall Plantation, near Chesapeake bay in the United States – once owned by William Paca, governor of Maryland, one of the signatories to the Declaration of Independence.
This is an extract from our feature The secrets of Angkor Wat: How archaeology is rewriting history. Read how the results of LiDAR surveying have revolutionised our understanding of the Cambodian temple complex in CWA 77. Click here to subscribe.