Improved magnetic sensor system technology is needed to address the environmental problem posed by hidden and buried unexploded ordnance (UXO) at sites such as Formerly Used Defense Sites and other closed or active weapons test ranges. In particular, this project’s research and development (R&D) effort addressed the need to develop improved man-portable sensing platforms and advanced signal processing technologies that will more efficiently and cost-effectively perform detection and discrimination of UXO. The R&D effort focused on development of (1) an improved man-portable magnetic sensing technology for real-time, point-by-point Detection, Localization and Classification (DLC) of magnetic UXO and (2) new signal processing approaches that will allow the portable sensor and other future sensor systems to perform more effective DLC of UXO in magnetically cluttered areas.
This project’s initial objective was to develop and demonstrate a man-portable magnetic sensor based on the magnetic Scalar Triangulation and Ranging (STAR) concept. Subsequent to the successful demonstration of the magnetic STAR (MagSTAR) technology, the project was extended with the objective of developing the technology for use in magnetically cluttered environments.
Researchers developed a new magnetic anomaly sensing-based technology concept for localization/classification of ferrous UXO-type targets. The new technology measures and processes scalar magnitudes of the gradients of the direct current (DC) magnetic anomaly fields that emanate from magnetically polarized ferrous objects. In the context of this sensor development effort, the term DLC means that the new technology will detect the presence of the ferrous objects, determine the object’s vector location, and measure the object’s magnetic dipole moment vector. Here the term “classification” signifies accurate measurements of the three-dimensional (3-D) vector components of a ferrous object’s magnetic dipole moment.
According to tensor theory, the magnitude (also denoted as “gradient contraction”) of the gradient tensor of a vector field is a rotationally invariant scalar quantity. Furthermore, electromagnetic theory indicates that the magnitude of the tensor that represents the gradient of the magnetostatic dipole field of a magnetically polarized object has a robust mathematical/geometrical form that is analogous to that of a central potential field that is centered on the source of the dipole field, that is, on the magnetic object or ferrous UXO. Therefore, a multi-tensor magnetic sensing approach that exploits the mathematical and geometrical properties of the tensor magnitude field should be resistant to the effects of sensor platform motion and be capable of true real-time DLC of magnetic targets. In particular, these theoretical considerations indicate that gradient contraction data from a properly designed, 3-D multi-tensor magnetic gradiometer can be used to perform point-by-point (standoff) localization and classification of magnetic UXO by applying a unique, motion-noise-resistant magnetic STAR concept.
The researchers first designed, constructed, and conducted preliminary tests at Naval Surface Warfare Center Panama City Division (NSWC PCD) of the prototype man-portable MagSTAR sensor system. R&D results included theoretical modeling of STAR sensor performance, development of algorithms (coded in MATLAB) for data acquisition, target localization and residual motion noise compensation, design and construction of the first man-portable STAR sensor, and laboratory and field tests of MagSTAR hardware and software subsystems, such as field sensing and signal processing elements.
Field tests of the prototype STAR sensor system, while being hand-carried by a single individual, consistently demonstrated near real-time (within a total system delay of about 3 seconds) point-by-point DLC of magnetic targets at ranges of 5 to 7 meters from a 14.5 amp x meter-squared (Am2) magnetic dipole target that was used to simulate the UXO signature of a medium-sized munition. The prototype MagSTAR sensor that achieved these results represents the world’s first successful man-portable magnetic sensor system technology for real-time point-by-point DLC of magnetic targets. Engineering issues such as mechanical instabilities and field sensing element drift due to thermal effects have limited the technology’s DLC range to about 60% of its theoretical range. These range-reducing effects have been characterized, and technically sound approaches for mitigating the effects have been identified.
In the follow-on work, the project team optimized the prototype MagSTAR sensor and developed improved signal processing algorithms for more accurate point-by-point localization and discrimination of magnetic targets in magnetically cluttered areas.
This project succeeded in developing a prototype MagSTAR technology that when fully optimized will provide the UXO remediation community new magnetic sensing system technology for faster, more efficient detection, DLC.
In addition to the MagSTAR technology’s potential value for UXO-related geophysical surveys, it could also provide an enabling technology for important Department of Defense applications such as Explosive Ordnance Disposal (EOD) and Mine Countermeasures (MCM). Furthermore, the technology will be readily adaptable to a wide range of military, commercial, and scientific geophysical survey applications involving high-mobility sensing platforms such as robotic ground vehicles and unmanned aerial vehicles.