Abstract

Numerous fatal encounters with large crevasses concealed by bridges of drifted snow have occurred on the Greenland icecap and elsewhere. In response to an urgent need for rapid and reliable means of crevasse detection, a promising geophysical method has now been developed for the Department of Defense. This method is analogous to the four-electrode method of measuring earth resistivities. It is different in that an alternating dielectric displacement-current field is employed rather than a field of conduction current since the ice medium is essentially a nonconductor. As a result, basic differences in technique are necessary. The systems tested in Greenland and Antarctica, to date, which employ this method, continuously indicate or record the capacitive transfer reactance between pairs of electrode sleds or vehicles. Systems have been operated successfully while in motion at surface speeds up to 20 miles per hour. Pronounced and distinctive electrical anomalies have been obtained at every crevasse tested to date. Typical crevasse-detector recordings and details of the equipment and techniques used are presented. Some potential applications of the mutual-capacitance method in mineral prospecting and other fields are suggested.

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