In France, during World War I, entrenched opposing armies faced off for years, persistently bombarding one another. It has been estimated that perhaps 10–15% of the shells that were fired failed to explode, at least initially. Many contained highly noxious substances in addition to explosives; consequently, a treacherous and sometimes urgent cleanup problem continues into the present. With no lack of local variations, it continues likewise in a great many regions throughout the world, including the United States. Recent US reports note that something on the order of 3,800 sites—tens of millions of acres—are potentially contaminated, most prominently at current or past military practice sites.1,2 Many of the subject lands are now desirable for other uses, but they must first be surveyed and certified safe within reasonable economy. However, detection and discrimination of UXO have presented daunting technical challenges. The false alarm rate under historical practices is typically enormous, and cleanup costs are very high: field experience indicates that more than 90–95% of excavated items may be nonhazardous scrap or fragments. The remote sensing technologies and conservative decision tools in use up to the present ensure numerous false alarms which, in turn, drives costs.
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