Current surface-based technologies have shown improvement in their ability to detect subsurface unexploded ordnance (UXO) but are unable to reliably discriminate UXO from other items that pose no risk. These approaches are also generally labor-intensive, slow, and expensive. Significant cost savings could be achieved if airborne methods were demonstrated to be an appropriate substitute for a portion of surface-based applications. Recent advances in airborne magnetic systems have enabled capabilities that are significantly improved over prior generation airborne-based systems. The objectives of this project were to (1) determine the viability of an airborne-based magnetic system for the detection and mapping of UXO and (2) demonstrate an airborne system for footprint reduction applications to delineate areas of concern.
The Helicopter-Mounted Magnetometer (HM3™) system employed had cesium vapor magnetometers mounted on the tips of three rigid 6-meter booms (one forward and two lateral) that were mounted on the underside of the aircraft. This configuration enabled a nominal instrument altitude of 1 to 3 meters above the earth's surface. Survey lines were interleaved so that three traces of total magnetic field data were collected for each flight line providing a nominal data profile spacing of 3 meters for flight line spacing of 9 meters.
Demonstrations were conducted in 1999 and 2000 at the former Badlands Bombing Range in South Dakota. They involved the detection and characterization of ordnance and ordnance-related debris at previously ground-surveyed locations, a large previously unsurveyed area, and a controlled test site using airborne magnetometer technology. Results validate this technology's utility as a practical and cost-effective method for the detection and mapping of UXO as well as wide-area surveillance associated with footprint reduction activities.
The primary benefit of this system is its capability to cover large areas of ground more quickly and inexpensively than conventional ground-based surveys. Where large UXO items are involved, the wider sensor spacing and higher altitudes found in airborne arrays result in minimal reduction of detection resolution. The airborne system also has an advantage in areas where ground access is limited or complicated by surface conditions (e.g., swamp or marsh), areas with inherent danger from exposure to UXO or other contaminants, and areas with a sensitive ecological environment. At the time of this demonstration, no competing technologies to the HM3™ were known to exist for airborne magnetic surveys.