Applied Geophysics and the Detection of Buried Munitions

Buried military munitions, such as bombs, artillery projectiles, rockets and landmines can present serious safety hazards. Geophysical investigations are often used to detect such munitions so that they can be safely recovered and destroyed. However, different geophysical methods each have particular capabilities and limitations. Magnetometers and gradiometers are well suited to detecting ferrous munitions to depths of two or three meters. However, they cannot detect non-ferrous munitions. Frequency domain conductivity meters are the best tools for detecting landmines containing very little metal; however, they are capable of detecting individual objects only to a depth of a few centimeters. Time domain conductivity meters can detect both ferrous and non-ferrous munitions and are effective to depths of only one or two meters. However they can be adversely affected by shallow groundwater. Ground-penetrating radar can be an effective tool for detecting munitions in sandy soils; however it is ineffective in clayey soils. In addition, Huntsville Center is developing geophysical data management and analysis software called the Ordnance and Explosives Knowledge Base (OE-KB) to improve the munition detection and recognition capabilities of geophysical investigations. However, even using best available hardware and software combinations, geophysical investigations to locate and identify buried munitions are seldom 100 percent successful and it is important to convey this limitation to all involved stakeholders. INTRODUCTION Buried munitions are a serious hazard at many locations both within the United States and overseas. Geophysical investigations are widely used to locate such munitions so they can be safely identified, recovered and destroyed. However, no single munition locator is effective for all types of munitions and in all locations. The purpose of this paper is to describe the main types of geophysical instruments currently in common use as munition detectors, to describe their uses and limitations, and summarize how the data from those instruments can be analyzed to facilitate ordnance detection. There are many geophysical and remote sensing techniques beyond those mentioned in this paper that have application to the detection of buried, surface, or underwater munitions. However, this paper summarizes the methods most commonly used and having widest application. BACKGROUND With the invention of durable, modern fuzed munitions around 150 years ago, a long-term munition safety hazard was created at battlefields and training areas worldwide. That hazard remains long after the soldiers have left. In the United States there are still occasional accidents involving munitions fired during the Civil War (1861-1865). In Europe, accidents involving forgotten munitions are much more common as a result of the two world wars during this century. In France, 630 demineurs (para-military explosive ordnance disposal specialists) have been killed since 1946. On the civilian side, 36 French farmers died in 1991 alone when their machinery struck unexploded shells. Worldwide, a subset of munitions-landmines, is a particular problem. According to the United Nations 110 million mines are buried in 64 countries, most of them unmarked. About 24,000 civilians are killed or maimed by those devices every year. Obviously, the detection and identification of buried munitions warrants a high priority in areas they exist. EOD Operations in Kuwait DETECTING BURIED MUNITIONS Evolution of Ordnance Detectors Military organizations first began fielding devices designed to locate buried munitions, particularly ferrous landmines, shortly before World War II. The first mine detectors generally operated on the principle of simple Report Documentation Page Form Approved