Laser scanners map rock art

Sid Perkins

From Philadelphia, at a meeting of the Association of American Geographers

Researchers have developed a way to use laser-based surveying instruments to create detailed images of ancient etchings on stone. The new technique, which provides far more information than photographs do, could enable archaeologists to quickly catalog the ancient rock art, or petroglyphs, at sites that are geologically unstable or vulnerable to theft or vandalism.

The prototype equipment uses a green laser beam that scans back and forth to generate three-dimensional maps of objects and terrain, says Thad Wasklewicz of the University of Memphis in Tennessee. Those maps, which can be compiled in just a few minutes, span a 40° field of view and contain up to 1 million data points—each of which is accurate to within 6 millimeters.

Ancient artists created petroglyphs by scraping away a dark, mineral-rich coating called desert varnish (SN: 1/3/04, p. 14: Available to subscribers at http://www.sciencenews.org/articles/ 20040103/note15.asp) to expose underlying light-colored material. The intensity of laser light that reflects off the varnish is different from that which bounces back from exposed rock. After field data have been collected, analysts can digitally assign a different shade of color to each intensity level of reflected light and thereby create high-resolution, false-color images of the art.

Wasklewicz and his colleagues field-tested their technique at a site near Little Lake, Calif., where some petroglyphs date back as long as 14,000 years ago. With their equipment, the researchers generated large-scale maps of the ancient lava flows, as well as detailed images of art on individual rocks. In some cases, the laser scans picked up the faint traces of ancient petroglyphs that couldn't be seen with the naked eye because they were obscured by a fresh coat of desert varnish, says Wasklewicz.

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Letters:

Using laser technology that has an apparent resolution of only about half a centimeter is somewhat laughable. I also wondered whether the "fresh coat of desert varnish" was an April fool joke. Actually, I really look forward to every new issue. You do a great job.

Fred Dombrose
Charlotte, NC

For images that weren't three-dimensional, the equipment produced detailed, 1-megapixel images, on par with many digital cameras. The "fresh" coat of desert varnish was several thousand years' of minerals deposited by the desert itself.—S. Perkins

References:

Wasklewicz, T., et al. 2004. A new technique for mapping petroglyphs. Annual Meeting of the Association of American Geographers. March 16. Philadelphia. Abstract.

Further Readings:

Perkins, S. 2004. New technique dates glaze on desert rocks. Science News 165(Jan. 3):14. Available to subscribers at http://www.sciencenews.org/articles/20040103/note15.asp.

Sources:

Thad Wasklewicz
University of Memphis
Department of Earth Sciences
113 Johnson Hall
Memphis, TN 38152-3550

From Science News, Volume 165, No. 14, April 3, 2004, p. 222.