Dig Diary: 3D Laser Scanning
by Steve Wilkes, Time Team America Surveyor
To help Duncan Metcalfe and his team of archaeologists record the conditions at Range Creek, Time Team America brought the latest in cutting-edge survey technology: 3D laser scanning. Enabling the remote collection of millions of individual measurements, laser scanners are changing the way we look at and analyze our surroundings. For Time Team America, the laser scanner enabled the recording and mapping of the existing conditions of the Range Creek site faster and in more detail than ever before.
The terrestrial laser scanner used by Time Team is known as a "Time of Flight" scanner. It works by firing out a laser beam and recording the time it takes to reflect back. This is very similar to some conventional survey equipment except that the scanner does this up to 50,000 times a second!
Each return of the laser is recorded as a co-ordinate X, Y, and Z point (or Northing, Easting, and Elevation). As more and more of the these tiny individual points are collected, the data forms a "point cloud," which starts to resemble the area being scanned. The more readings that are taken, the more detailed this point cloud gets. Since each point is an individual reading, any detail recorded can be measured and mapped with high precision and accuracy. A camera inside the scanner also takes a panoramic photograph of the scene being scanned. Every point collected has a color assigned to it based on this panorama, which can provide an important visual 3D record of the site conditions like never before.
Archaeologists are just beginning to explore ways to apply 3D laser scanning to their research. One California-based non-profit organization, CyArk, is using the technology to record important heritage sites around the world -- such as the Mayan city of Tikal and Mesa Verde in Colorado -- as a way of digitally preserving them. Laser scanning data provides the most detailed and accurate 3D record of a building, statue or artifact currently available to archaeologists and historians. This data provides a highly-detailed archive of information that can then form the basis of reconstructions or collaborative analysis between researchers. It also means that any restoration projects that take place on a site can also benefit from a stone-by-stone record of a structure. If elements have to be taken off site for conservation, they would then have a detailed record of its position and be able to return or rebuild accurately. Time Team America used the laser scanner to record some of the Fremont rock art in the canyon. Not only did it record the petroglyphs for future research, but the laser scan also revealed new details in the drawing not easily visible to the naked eye.
Laser scanning is also used as a tool for topographic mapping, the basic survey work of an archaeological site. Laser scanning, when combined with traditional survey, can record a site quickly and accurately and in far greater detail. The incredible data it captures provides a rich resource for mapping and analysis, even after you have left the site. Just like conventional survey equipment, the scanner can also be positioned over survey control points, enabling all the digital site data to be related together. Future work could see the marrying of the geophysical and survey data into the 3D scanned environment. The amount of detail that can be recorded for a landscape also allows for micro-contouring which can often show topographic change caused by subsurface features.
Click to view LIDAR images taken at Range Creek: