Well-developed standardized methodologies and approaches for assessment of terrestrial munitions and explosives of concern (MEC) exist; however, there are currently no standardized approaches for wide area assessment (WAA) of MEC in freshwater or marine environments.

The objective of this demonstration was to address the lack of a standardized approach for detecting and locating underwater MEC over large areas.

Tetra Tech EC, Inc. (TtEC) developed an approach utilizing multiple underwater detection and mapping technologies and instruments to acquire data sets, which were then used to evaluate ordnance-related conditions and geophysical features representing potential underwater MEC. The platform used for collecting magnetometer data was TtEC’s Marine Gradiometer Array (MGA), which houses instrumentation demonstrated to be effective for the location and identification of MEC in marine or freshwater environments.

Quantitative and qualitative objectives were developed to assess system performance. These objectives and their summarized results included the following:

• Demonstrate ability to detect underwater features of interest and measure the system’s ability to effectively detect targets of interest with magnetic signatures representative of MEC at water depths from 0.5 to 35 meters (m).
• Results: The MGA met the data quality metrics as verified by instrument validation strip (IVS) results and was successful in all water depths (demonstrated at this and other sites).
• Demonstrate timely initial data processing and mapping and provide a qualitative and quantitative assessment of processing times for multibeam echosounder (MBE) data, which is needed to map site bathymetry, locate debris proud of the bottom, and guide MGA data acquisition.
• Results: Survey technicians were able to process the MBE data onboard the vessel and generate draft charts in near real time. On some survey days, MBE data were collected in the morning, processed, and then used in the afternoon to guide MGA data acquisition. TtEC considers this level of efficiency to be quite successful.
• Demonstrate good production rate—this is a measure of the system’s capability to meet established hourly/daily production rates while meeting data quality objectives.
• Results: Quantitative goals set forth in the Work Plan, which were derived from previous experience and theoretical production rates based on survey speed and number of operational hours possible in a day, were met and exceeded. TtEC was able to exceed the projected MBE production rate by more than 50%.
• Demonstrate ease of use—this qualitative objective assesses the ease of implementing the WAA survey for both data collection and data processing.
• Results: Support vessel customization has resulted in a platform well-suited to conduct underwater MEC surveys anywhere in the continental United States. MGA data processing objectives were exceeded due in part to software development funded in part by the Department of Defense’s (DoD) Environmental Security Technology Certification Program (ESTCP).

Using the MGA system to conduct WAA of MEC has several benefits:

• The MGA system is modular and can be disassembled and shipped via FedEx or other freight carrier to any location in the world.

• The modular configuration allows the system to be used in shallow (1 m and less), medium (1 m and up to 35 m), and deep water (35 m and up to 300 m) by altering the system’s setup and tow method.

• The system has a rugged construction, with a weak link that allows for safe detachment from the tow cable while maintaining tracking with ultra-short baseline acoustic positioning system should the towfish contact the bottom. (Note: this functionality performed successfully during the demonstration project survey with no damage to towfish and only minutes of lost survey production.)

• The Overhauser magnetometers used in the MGA system have several advantages: (1) clear, strong proton precession signals using a small amount of power; (2) sensitive to changes in the geomagnetic field and not influenced by a phenomenon termed “heading error”; (3) sensor measurements are temperature independent, avoiding any system drift; and (4) simplified processing and data analysis due to eliminating correction for sensor drift, orientation, and heading error. In addition, the design of the MGA allows the total magnetic field for each magnetometer to be measured, as well as up to 10 two-dimensional magnetic gradients and 3 three-dimensional measured analytic signal vectors measurements. This system is unique in that it provides both total field and vector data.

• The MGA system is highly cost competitive with existing technologies when employed in combination with the data collection and processing tools and methods used in this demonstration project. This competitive cost is provided while detecting MEC over large areas and achieving reliable anomaly locations (approximately 89% of checks on IVS were located to within 2 m and approximately 47% were located within 1 m).

Overall, the WAA method using the MGA is shown to provide accurate and low cost surveys of MEC in marine and freshwater environments than current methods.