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SCIENCE OBSERVER

Fossil Hunting, by Radar

Rebecca Sloan Slotnick

Although paleontologists can still be found crouched amid crumbled rock, picking away with small dentist's instruments, they might also be found in some unlikelier places. In a dirigible, say, floating over the Sahara Desert.

At least that's where North Carolina State University physicist Michael Paesler hopes to be someday. Paesler, in association with the Center for the Exploration of the Dinosaurian World, proposes using airborne radar sources to quickly survey large surface areas for dinosaur remains.

Simulation of the Mineseeker dirigibleClick to Enlarge Image

The Sahara is an ideal backdrop, Paesler says, because it is vast but uniform and composed almost exclusively of anhydrous silicon dioxide—dry sand. Flying at altitudes of up to 2,500 kilometers, an airship equipped with a small antenna sends a series of pulsed radar signals at ultrawide band (UWB) frequency down to the ground, where they are reflected by the sand. By coupling a steadily moving source and detector, a "synthetic aperture" is created, simulating a larger antenna and increasing resolution across the field. According to Paesler's model, some of these radar pulses penetrate the desert surface and are reflected by buried deposits of calcium phosphate—the primary material of which bone is composed.

Preliminary tests, performed in the laboratory, indicate that the indexes of refraction values of sand and fossil are significantly different and that ground-penetrating radar (GPR) should effectively differentiate between the two. Paesler is now seeking funding for a pilot project he hopes to get off the ground within a year. The team aims to demonstrate that remote-sensing radar can "detect, localize, and resolve an object with size, mass, and dielectric response essentially identical to that of a dinosaur fossil" even tens of meters below the desert surface, according to the preliminary proposal. They plan to bury a "phantom" fossil, composed of calcium phosphate, beneath dry sand and attempt a recovery.

Despite the simplicity of his proposed technique, Paesler hasn't found much record of fossil recovery using remote-sensing radar—only a small study in the early nineties at Bone Cabin Quarry, an area of the Midwest in which large quantities of dinosaur remains were (and are still being) discovered. The tests were performed by sweeping a GPR system along the ground in areas known to contain dinosaur remains. The scientists met with limited success for several reasons cited in the paper, published in the 44th Annual Field Conference of the 1994 Wyoming Geological Association Guidebook. Little contrast was found between the embedded fossil and surrounding rock, and the surface proved to be irregular. GPR techniques did save the paleontologists some digging, but they were only able to record an average depth of 3.4 feet below the surface.

More recently, synthetic aperture radar (SAR) has been used by military forces to locate land mines for humanitarian purposes. The Mineseeker blimp, developed by the Defence Evaluation and Research Agency and the Lightship Group in the United Kingdom and requested by the United Nation's Mine Action Coordination Centre, made its first foray into Kosovo in mid-November. Preliminary analysis of the results suggests that the airship successfully detected mines with at least the frequency of prior methods. The principles of physics used for remote-sensing radar recovery of land mines and fossils are quite similar. "The military is searching just below the surface for mines, while we will be looking deeper beneath the surface for bones," says Paesler.

Not only does the discovery of fossil remains using remote-sensing GPR or SAR speed up the formerly slow and painstaking process of hit-or-miss digging at select geographic locations, but it may even improve the quality of the fossils recovered. Dinosaur remains emerge from the ground as it erodes from wind and water exposure. Any exposed bones found by a paleontology team toiling at the surface, then, have been sandblasted by the wind—subject to what paleontologists call aeolian abrasion. SAR technology could potentially allow fossils to be uncovered before they have surfaced, resulting in the discovery of better preserved specimens.

Paesler stresses the preliminary nature of his proposal; he hopes to be unearthing "phantom" fossils by the end of the year. And although the location of his phantom digs is still undecided, he mentioned the existence of sand mines in North Carolina—which, he points out, was neighbor to Morocco 200 million years ago—the intended site in the Sahara Desert of his first true remote-sensing radar search for dinosaur remains.—Rebecca Sloan Slotnick


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