Recent advances in airborne survey technology yield performance approaching ground-based surveys

Abstract

Airborne magnetic and electromagnetic systems have been very effective over the years for mineral prospecting and in support of petroleum exploration. More recently, these towed-bird systems, operating at sensor altitudes of 30–50 m, have supported environmental investigations. The towed-bird systems can provide regional data for site investigations, such as locating or delimiting the boundaries of waste areas, identifying geologic contacts that influence environmental issues, or mapping saline intrusion. However, these conventional systems cannot provide the resolution required in many environmental and engineering problems because the distance between sensors and target objects is too great. Ground-based surveys are often suitable for addressing these problems but, for many sites, the area can be too large to be expediently addressed with surface geophysics. Contamination of government land with unexploded ordnance (UXO) is one such large-scale problem. As military bases are being closed and returned to civilian use, the removal of UXO has become a critical problem. By one estimate, about 11 million acres within the United States, roughly the sum of the areas of the states of New Hampshire and Vermont, are contaminated with UXO. This includes Department of Defense (DOD) sites, Department of Energy (DOE) sites, Native American sites, and National Park lands. At some DOD sites, large areas are currently off limits for training pending removal of UXO. In other parts of the world, UXO threatens people's lives every day. In the 1990s, two coauthors of this article, Holladay and Gamey, began to address the UXO problem while working at Aerodat in Toronto. They devised a three-magnetometer system, the HM-3, in which the sensors were mounted in booms attached directly to the helicopter. This architecture provided an opportunity for the pilot to safely fly much closer to the surface. During subsequent joint projects with Oak Ridge National Laboratory (ORNL) researchers, both …