Laser scanners map rock art

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

ANCIENT SCRAPES. Petroglyphs at a site near Little Lake, Calif., as seen in visible light (above) and in a false-color, laser-scanned image (below). Wasklewicz


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 New technique dates glaze on desert rocks) 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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