Chemistry Division Team Receives ESTCP Award for Airborne MTADS Array

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Scientists from the Naval Research Laboratory's Chemistry Division received the Project of the Year Award from the Environmental Security Technology Certification Program (ESTCP). ESTCP is the Technology Demonstration Validation Program managed by the Office of the Deputy Undersecretary of Defense for Installations and Environment (DUSD/I&I). Principal investigators Dr. Herb Nelson, of the Chemical Dynamics and Diagnostic Branch, and Dr. Jimmie McDonald, a former Chemistry Division employee who is now with AETC Incorporated, were commended for developing and demonstrating an airborne version of the Multi-sensor Towed Array Detection System (MTADS) for large-scale unexploded ordnance (UXO) geophysical surveys.

The award citation states, "Airborne MTADS has proven to be an efficient and highly reliable survey platform against a variety of ordnance threats. Already, geophysical investigations on several ranges, including the Badlands Bombing Range in South Dakota, the Aberdeen Proving Ground in Maryland, and Isleta Pueblo in New Mexico, have demonstrated the airborne MTADS to be an effective and reliable means for UXO detection and mapping. This is truly a capability that we have never had before. It will improve the ability of the Department [of Defense] to prioritize and conduct cleanups, as well as save the Department millions of dollars."

Dr. Jeffrey Marqusee, ESTCP Director, on presenting the award, explained, "Many formerly used ranges that are contaminated with UXO are thousands of acres in size. Wide-area assessment tools that can survey large tracts of land efficiently are required, but traditional ground-based survey procedures are too inefficient and costly. Accordingly, a long-standing Defense priority requirement has been to produce an efficient and economical survey system with production rates and costs appropriate for large areas."

The vehicular MTADS, or Multi-sensor Towed Array Detection System, which was originally developed by Drs. McDonald and Nelson under ESTCP sponsorship, provided a reliable UXO surveillance system that typically surveys tens of acres per day. Dr. Marqusee added, "However, at this rate, it would take 750 days at $400 to $800 an acre to survey a typical 15,000 acre range. Clearly, the survey rate had to go up and the costs come down."

Drs. Nelson and McDonald adapted the MTADS magnetometry technology for deployment on a helicopter platform. "The airborne MTADS has demonstrated survey production rates up to 500 acres per day at a cost of $100 per acre - an order of magnitude reduction in cost from traditional mag and flag survey methods," concluded Dr. Marqusee.

"Mag and flag" refers to the traditional way of finding UXO, where technicians walk survey lanes laid out in a field, swinging a metal detector in front of them. The most commonly used detector for UXO is a magnetometer, hence the "mag," explained Dr. Nelson. The magnetometer, similar to the sensors on the MTADS, detects perturbations in the measured magnetic field due to buried ferrous metal objects, including iron bombs, projectiles, and mortars. When the UXO technician gets a "hit" from the instrument, he puts a flag in the ground and later comes back to dig up the source of the signal, hence the "flag." "The problem with this [method]," Dr. Nelson added, "is that since the anomaly strength falls off as the cube of the distance from detector to the object, small, shallow things, like fragments from explosions, give big signals in one spot while large, deep things, like bombs, give smaller signals over a much larger area." Overall, the mag and flag method tends to give a lot of false alarms - not false in the sense that no metal is there, but false in the sense that the thing identified is not dangerous - and tends to miss deeply buried bombs, added Dr. Nelson. In addition, the mag and flag method depends on the concentration level of the operator, which varies as the day goes by. Because it costs about $200 to have a potential UXO target dug up for investigation, identifying too many fragments drives the costs up substantially, explained Dr. Nelson.

Beginning in 1995, the vehicular MTADS was developed by Drs. McDonald and Nelson under sponsorship from ESTCP, a corporate Department of Defense (DoD) program that promotes innovative, cost-effective environmental technologies through demonstration and validation at DoD sites. MTADS consists of trailers with arrays of sensors that were towed by a dune buggy-like vehicle. The vehicle system was a big advancement from the mag and flag method. It proved to be an excellent detection system, with the capability to cover approximately 20 acres a day, providing reliable and accurate data. The vehicular MTADS technology was later commercialized through a Cooperative Research and Development Agreement (CRADA) with Blackhawk Geometrics, of Golden, Colorado.

But, because many ranges are 10,000 to 100,000 acres, there was a need for a system to cover large areas. Thus, Dr. Nelson and McDonald were sponsored by ESTCP to develop and demonstrate an airborne version of MTADS that had all the capabilities of the vehicular MTADS, but increased the coverage to 400 acres a day.

The objective of the airborne MTADS array project was to design and build an efficient and economical UXO survey system, in which production rates and costs were appropriate for surveying of large tracts of land. This system was designed to locate buried caches of ordnance and to confirm areas that are "uncontaminated." It also retained all the basic MTADS capabilities of detecting, locating, and identifying individual ordnance items. According to Dr. Nelson, the airborne MTADS system is capable of detecting ordnance of 2.75-inch rocket warheads and larger.

In explaining how the system works, Dr. Nelson described, "The system deploys a linear array of 7 Cs-vapor magnetometers spaced at 1.5-meter intervals in a forward-mounted boom. The system is certified for operation on all models of the Bell Long Ranger helicopter with high skids. Two Global Positioning System antennas mounted on the forward boom provide positioning and helicopter roll and yaw measurements. An inertial measurement unit in the aircraft and a 3-axis fluxgate gradiometer, also located in the sensor boom, redundantly provide additional attitude measurements. Laser, radar, and acoustic altimeters provide altitude information. A pilot guidance display provides survey progress and platform information in real time. The data acquisition electronics rack, mounted in one of the rear seat positions, is interfaced to all system components."

According to ESTCP, it is estimated that in excess of 10 million acres of land in the continental United States may be contaminated by UXO. MTADS was developed as a state-of-the-art vehicular towed array for large-scale UXO geophysical surveys. The airborne MTADS project, an analog of the vehicular MTADS, permits surveys of areas that do not hospitably support vehicular towed arrays, e.g. because of rough terrain or vegetative ground cover.

Also noted on the award citation are Mr. David Wright and Dr. Nagi Khadr, of AETC, Inc. Mr. Wright was the major contributor on the hardware issues and Dr. Khadr was the lead on software analysis issues.

A CRADA for the airborne MTADS is being negotiated with Sky Research, of Ashland, Oregon, to commercialize the airborne system.

Airborne MTADS magnetic anomaly map of the Impact Area at the Badlands Bombing Range, SD, showing the main bull's eye in the middle of the area, with significant numbers of UXO throughout the site.

The MTADS Family - The man-portable array (left foreground), the vehicular array (right foreground), and the airborne magnetometer array.

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