Multi-Sensor Towed Array Detection System (MTADS)
Traditional detection and characterization technologies for unexploded ordnance (i.e., bombs and shells, or UXO) involve hand-held magnetometers operated by technicians who must slowly walk across a survey area. When the detector indicates a ferrous object, the operator marks the location. Known as the "Mag and Flag" method, it is time consuming and dangerous, as well as inefficient. Many ordnance items are often disguised by the presence of extensive "clutter" on the land surface. Large and deep ordnance items are often not found because they are difficult for an operator to "visualize" because large items generate such large magnetic fields that it's sometimes difficult to pinpoint or even notice them against a background of magnetic disturbances. In 1992 the U.S Army Corps of Engineers estimated that more than 50 percent of the area at UXO sites could not be surveyed using the hand-held approach. Also, conventional "Mag and Flag" produces no certifiable survey product, and quality assurance and quality control are difficult. The Multi-Sensor Towed Array Detection System (MTADS) technology is designed to address these issues. It should be noted, however, that other technologies have been developed to address some of the shortcomings of the "Mag and Flag" approach.
The MTADS tow vehicle is a custom-built off-road vehicle, specifically modified to have an extremely low magnetic signature. It is equipped with an array of passive magnetic and active electromagnetic induction sensors that digitally record evidence of buried UXO or large metal objects such as drums and storage tanks. Advanced systems are also equipped with an array of chemical sensors and a Global Positioning System (GPS) device to detect and map the location of buried UXO. The MTADS enhances the speed of detection typically by a factor of ten compared with the Mag-and-Flag method. The system can survey 10 to 25 acres per day and provide data at high density (70,000 to 100,000 measurements per acre). The electromagnetic induction sensor detects small ferrous and non-ferrous materials. (Some munitions are made of non-ferrous metals. Most artillery fuses are non-ferrous and are still hazardous if they have separated from the projectile. Many very small ferrous items cannot reliably be detected by magnetometers.)
An advanced system of MTADS places the platform on a helicopter. This permits the system to detect and classify targets the size of general-purpose bombs or large caliber shells over large areas and areas not amenable to vehicular based surveys. Airborne magnetometry has been used in DoD programs associated with airborne submarine detection and in the commercial geophysical mining exploration arena. The effects of platform-induced magnetic noise can be minimized by the application of aeromagnetic compensation techniques that account for pitch, roll, and yaw and altitude.
Limitations and Concerns
Vehicular towed systems are limited, primarily because of difficult topography and vegetation. Satellite-positioning technology and alternative navigation systems under consideration will not increase the potential survey area significantly. GPS navigation is limited to areas with good sky view, limiting operation in heavily wooded areas. In areas where GPS reception is not possible, an alternative location system, such as acoustic or laser navigation, may prove useful. As an alternative, a one-person portable detector equipped with ultrasonic ranging may be used when GPS signals are degraded due to vegetation.
No existing technology for characterizing buried UXO achieves the 100% detection rate sought by many neighbors of military property containing UXO, though they approach that for items on or just below the surface.
MTADS is a characterization technology that may enhance the safety, speed and thoroughness of environmental clean up. Because conditions vary from site to site, other munitions characterization technologies, it must be validated for each deployment.
Data interpretation is a key to the success or failure of this technology.
Magnetic and electromagnetic detectors have diminished accuracy in highly magnetic soils.
MTADS is primarily designed to detect UXO in soils (i.e., up to 25 feet for large objects and up to 3 feet for small objects). It is also capable of locating ferrous objects such as buried drums in landfills. The U.S. Department of Defense (DoD) is responsible for over 15 million acres of weapons ranges in the United States, and over 1,500 sites may require the cleanup of UXO.
Technology Development Status
MTADS using a magnetometer and an electromagnetic induction device has been used successfully, and it is a commercial technology.
Other Resources and Demonstrations
See ESTCP UXO Cost and Performance Report, Multi-Sensor Towed Array Detection System (MTADS), September, 1999. See http://www.serdp-estcp.org/content/download/4446/66132/file/199526.pdf
See http://www.serdp-estcp.org/Tools-and-Training/Munitions-Response/Wide-Area-Assessment for multiple descriptions of airborne assessments using similar sensors.