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What Lies Beneath: Detecting Bombs Under the Earth's Surface

Paul Lima

With the growth in global population, land for housing, business and recreation is in great demand. However, land that seems available might not be suitable for human use if it has served as a battleground in warfare or if the military has used it for practice ranges or the disposal and destruction of munitions. Land mines and unexploded ordnance (UXO) contaminate more than 83 countries. When munitions are fired but don't explode or only partially explode, they are categorized as UXO. Battlegrounds in the First and Second World Wars are a typical example of UXO fields. UXO can also be found in regions of developing nations in the 20th and 21st centuries where civil or proxy wars have been played out (such as occurred in the Cold War). These fields are scattered around the globe. In the U.S., more than 2,000 closed or transferred military ranges are believed to contain UXO. Before land with buried UXO can be reclaimed for housing or other projects, the UXO must be found and removed.

The UXO Detection Challenge

Locating and removing UXO can be complicated, time-consuming and costly. In Europe, there is growing advocacy for UXO and mine clearance, with stronger partnerships emerging between UN, community and government agencies to set out plans for UXO removal. Standard UXO detection techniques in Europe generally make use of traditional grid-pattern borehole drilling. In North America, the civil engineering arm of the military is in charge of UXO clearance. UXO teams in North America, working under guidelines set by the U.S. Army Corps of Engineers (USACE), collect and analyze data for UXO removal with the aid of geophysical techniques and specialized software.

"If we had to remove bombs from flat homogeneous areas such as sand bars, we could easily detect the UXO with geophysical sensors and they would stick out like sore thumbs, but that's seldom the case," says Elizabeth Baranyi, Earth Sciences application programmer with Geosoft.

In areas that are rough or wooded or where the soil is magnetic or covered with lava flow that has a high iron content, sensor readings become busy, making it difficult to distinguish between geological and UXO signals. Other buried objects of similar size, such as a metallic grid, can further complicate the interpretation of data. The discrimination between UXO and non-UXO is a cost concern that is a subject of ongoing research.

Precision and data quality is critical in UXO surveys; all external factors must be minimized as they can interfere with the reading of UXO signals. Examples include steel-toed boots, jangling keys, flopping cables, and even inconsistent walking speeds.

Before the introduction of software, contractors used instrumentation to locate UXO and dig where they found peak readings. This method was knows as "Mag and Flag." "However, the peak isn't necessarily right above the UXO," says Baranyi. "It depends on the size, shape, depth and dip angle of the UXO, and, in the case of magnetic surveys, the magnetic field of the earth. You can dig at the peak and miss the target by a few centimeters, or you might spend a lot of time digging for objects only to find they aren't UXOs." The aim is to improve the quality and the discrimination methodology of the UXO survey data in order to save time and money while ensuring confidence in the outcome.

Since there could be a large number of ordnances in a small area, or a few deadly ones spread over a large area, trying to pinpoint UXO locations is like looking for needles in a haystack – or, as in geological exploration, looking for a rare mineral that might or might not be present. But the process is getting easier, thanks to advanced geophysical techniques, computer-aided analysis, and 3D modeling.

Initial Planning

Exploring for UXO typically starts with initial geophysical planning. A geophysical investigation system capable of pinpointing buried UXO must have four fully integrated components:

• Personnel experienced in the theoretical and practical aspects of detecting UXO and discriminating between UXO and non-UXO. The selection and utilization of geophysical equipment require qualified, experienced individuals.
• Geophysical instruments that are well-suited to detecting buried UXO, taking into account site-specific factors such as the type and depth of the target UXO, terrain, vegetation, and geologic and cultural settings.
• Navigational accuracy and precision, that is, the ability to locate, within the centimeter range, the geophysical data in relation to other known points.
• Procedures for analyzing and interpreting geophysical data generated by geophysical instruments.

If any of the above four components are lacking, the overall geophysical system will not be able to locate UXO precisely. It's important to plan and integrate all aspects of a geophysical investigation carefully and not start fieldwork prematurely.

Geophysical Techniques

Geophysical investigations performed at sites that may contain ordnances can be divided into three categories:

• Geophysical sampling performed at representative portions of a site to characterize a larger area. The objective here is to characterize the distribution, type and condition of UXO across a site in a way that is both economic and accurate.
• Geophysical mapping performed across an entire area suspected of containing UXO. The objective is to locate all detectable UXO that meet pre-determined criteria such as type, size, composition and depth.
• Geophysical interrogation performed at specific locations or small sites to obtain additional target information beyond that gathered by initial investigations. Although slow and expensive, this technique can yield important information about the size, depth, composition and configuration of individual targets or target clusters.

Overall, the objective of such geophysical investigations is to locate UXO while minimizing the number of non-UXO geophysical anomalies. Since unearthing buried munitions is expensive, the data collected must be scrutinized carefully, and computer software is used to help with the analysis and for quality control.

Software for UXO

UXO investigations require the use of digital geophysical mapping software and depend on quality field data. The software is used to minimize the risk of inconsistent data and faulty decision-making. For instance, data filtering algorithms can level and smooth data, eliminate background noise, and enhance geophysical real anomalies that have UXO-like signatures. Software can also help convert high volumes of geoscientific data into knowledge that supports accurate UXO mapping and target detection and narrows selections to a final target list.

As part of its mandate, the U.S. Army Engineer Research and Development Center (ERDC) has been funding the development of technologies for the detection and discrimination of UXO in an effort to improve the process.

One of these initiatives, a co-operative agreement between Geosoft and the USACE, Huntsville Center, has resulted in industry-standard tools to boost efficiency and accuracy in UXO investigations. These UXO Quality Control and Quality Assurance (QAQC) software tools, developed within Geosoft's Oasis montaj platform, are being used at UXO sites around the world to improve data consistency and detection methods.

Beyond quality control, software is essential to UXO project management insofar as it allows work to be recorded, both for review and future audit. With all UXO investigations, it's necessary to demonstrate that the site was cleaned up as well as possible and that everything that was conceivably detectable – based on available scientific and technical capabilities – was in fact detected.

In short, software and quality control measures are essential both for the interpretation of data and the creation of standardized analytical processes. With advancing techniques and the right software, it's possible to manage UXO projects effectively, saving limbs and lives in the process.