The MetalMapper is the first commercially available instrument that collects electromagnetic data in three dimensions to permit the geophysical classification of subsurface anomalies. It is used to distinguish unexploded ordnance (UXO), discarded munitions, and similar items from metallic "clutter."
Much of the effort and expense at a typical munitions response site is expended on the wasteful excavation of objects such as horseshoes, nails, and pieces of barbed wire, as well as "frag," metal from exploded ordnance.
Previous technology, such as single-dimension active electromagnetic induction devices and passive magnetometers, can detect buried metal, but they do not collect enough information to determine whether such anomalies are likely to be explosive ordnance. Typically, using older technology, hundreds of anomalies are excavated for each item of live ordnance found. At Camp Butner, NC, only 0.03% of all excavations were unexploded ordnance (146 out of more than 500,000 digs).
After using conventional detection devices to detect and map subsurface anomalies, the MetalMapper is used to conduct a "cued" investigation. That is, it is placed above each anomaly. It transmits electromagnetic signals in three dimensions, and it then records the return electromagnetic signals in three dimensions. Specially trained geophysicist use those signals to determine the shape and other characteristics of each item, and they compare the collected data against signals documented in a "library" of known munitions. They use the data to compile a "dig list." UXO technicians then excavate all anomalies labeled likely or uncertain ordnance by the geophysicist. In most cases, only a fraction of those items labeled explosive turn out to be non-explosive. (Inert versions of explosive munitions are appropriately treated as explosive.)
The effectiveness of MetalMapper and geophysical classification have been demonstrated at several sites, where the area has first been "seeded" with inert UXO shells and other metal objects. This provides a real-world scenario that accurately determines system performance. Geophysicists create dig lists, and then technicians dig all known anomalies to determine how accurate the classification process, using MetalMapper, has been. The MetalMapper technique has been nearly 100 percent successful in identifying all UXO. When used at non-demonstration sites, it should significantly reduce excavation, cutting project costs by more than half.
Limitations and Concerns
MetalMapper only helps classify known anomalies for excavation. No existing technology for finding buried metal finds 100% of all buried UXO and discarded munitions, so MetalMapper doesn't solve that problem.
For optimum effectiveness, MetalMapper must be placed just above the ground's surface. It is difficult to bring the large, vehicle-towed MetalMapper to all anomalies found in rugged topography and dense vegetation, though in many cases vegetation can be cleared. Other, smaller instruments are being developed to conduct cued investigations in difficult-to-reach areas.
Early versions of MetalMapper tended to break down because they were not fully hardened for field use.
While GPS navigation is normally used to guide MetalMapper to known anomalies, other methods must be used on land, such as heavily wooded areas, where GPS signals are not accurate.
Correct data interpretation is essential to the success or failure of the MetalMapper. Analysis must therefore be carried out by qualified geophysicists.
Electromagnetic detectors, including MetalMapper, have diminished accuracy in highly magnetic soils, such as the iron-rich volcanic soils in Hawaii and basalt on the U.S mainland.
The MetalMapper is used to distinguish between UXO and clutter at sites where anomalies representing potential UXO have already been mapped. In the future MetalMapper or other instruments may be used to detect and classify anomalies at the same time.
Technology Development Status
The MetalMapper is commercially available. It is undergoing final pilot tests under the auspices of SERDP-ESTCP.
Other Resources and Demonstrations
A portion of former Camp Sibert, Alabama, a site with a single munitions type and benign conditions, was selected as the first site in 2007 to establish a performance baseline. At this simple site, well over half the clutter could have been excluded from excavation and nearly all the munitions correctly classified.
A demonstration at a more difficult site, the former Camp San Luis Obispo, California, followed in 2009. The hillside range used for the demonstration contained four known munitions types: 60-mm, 81-mm, and 4.2-inch mortars as well as 2.36-inch rockets. Three additional munitions types were discovered during the course of the demonstration. MetalMapper data collected resulted in correct classification of nearly 1,000 of the approximately 1,300 non-munitions items while identifying 100% of the targets of interest.
http://www.serdp-estcp.org/News-and-Events/In-the-Spotlight-Archive/Success-Classifying-Small-Munitions-at-Camp-Butner. In 2010, a demonstration was conducted at the former Camp Butner, North Carolina. This site is known to be contaminated with items as small as 37-mm projectiles as well as fragments from larger munitions, adding yet another layer of complexity. The advanced sensors were able to correctly identify all UXO while correctly classifying more than 1,900 of the 2,100 clutter items.
See also http://www.cpeo.org/pubs/StakeholderMRForum.pdf CPEO's report on Stakeholder views on the use of geophysical classification to limit dig lists.
For general descriptions of munitions response detection and removal, see the following: