LIDAR for History and Archeology

NOTE: This is an adaptation of an article written for the Northwest Hills Civic Association (NWACA) newsletter.

For orientation, black dot is intersection of Far West Blvd. and Mesa Drive in Northwest Hills. Click to enlarge.

You’ve probably heard of LIDAR. It’s what enables many self-driving cars to sense their surroundings. OK, except maybe Elon Musk who thinks it’s "expensive, ugly and unnecessary". But even he may be re-thinking LIDAR. LIDAR (Light Detection and Ranging) works by emitting laser pulses, then measuring the time it takes for the pulses to travel to objects and back, using this information to create detailed 3D models of objects.

But rather than mounted to a car, LIDAR can also be mounted below an aircraft, drone or even satellite to build digital elevation models of the earth’s surface; “bare earth” models excluding trees, buildings, and other surface objects. This has been a game-changer in fields like archeology enabling the detection and mapping of features – old trails, structures, burial depressions, geologic features – that are hidden beneath dense vegetation and hence not visible in aerial photos, and which can also be difficult to access and survey in person.

In the news a commonly reported use in archeology has been the detection and mapping of lost Mayan cities in the dense jungles of Central America where many Mayan ruins are hidden beneath the jungle canopy. Here in Travis County we have a similar problem; rather than jungle, we have trees and other vegetation covering much of the county, for example in the Balcones Canyonlands Preserve (BCP) west of our neighborhood. While a preserve now, this was home to Native Americans for thousands of years, and starting in the 19^th century European American settlers constructing ranches and farmsteads.

I recently had a chance to examine several sites in the BCP with USGS LIDAR data. One site we visited a few years ago, about 6 miles northwest of the neighborhood, was a collection of stacked limestone walls. It was quite a hike reaching them through a thicket of trees and brush, and once there it was hard to make sense of the layout. Oral interviews collected by archeologists when the area was acquired by Travis County for inclusion in the BCP suggested the site had been a stage stop along a historic road from old Jollyville[1] to Anderson’s Mill, with nearby springs for passengers to enjoy. With LIDAR the assemblage of old roads to and from the site, layout of corrals and buildings, and location of springs in nearby rock shelters became very apparent.

A drawback with LIDAR is that the data reflects the time at which it was collected. Since it is a relatively new technology, many areas you’d like to investigate have already been developed, hence the LIDAR is reflecting the development, not features of a historic site. Still with areas like BCP and other preserves like those in our neighborhood’s canyon lands it is a powerful tool for “seeing” what is there hiding beneath the dense overgrowth.

LIDAR data is publicly available in varying resolutions through the USGS. Included here is a birds eye LIDAR view of our own NWACA neighborhood. Enjoy.

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[1]For more on Jollyville, see What's Up with Jollyville Road?