Improved magnetic STAR methods for real-time, point-by-point localization of unexploded ordnance and buried mines

There is a pressing need for a practical and effective magnetic sensing technology that can be deployed onboard highly maneuverable sensing platforms and used for real-time, point-by-point detection, localization and classification (DLC) of magnetic targets such as ferrous unexploded ordnance (UXO) e.g., bombs, buried mines and artillery shells. Therefore the Strategic Environmental Research and Development Program (SERDP) has supported research and development, by Naval Surface Warfare Center Panama City Division (NSWC PCD), of a novel man-portable Magnetic Scalar Triangulation and Ranging (i.e., "STAR" and/or "MagSTAR") technology for DLC of UXO. The STAR concept uses scalar magnitudes of magnetic gradient tensors to triangulate the locations of magnetic targets. The magnitudes are analogous to central potential-type functions and they can provide true point-by-point DLC capabilities for sensing platforms in general, unconstrained motion. A prototype man-portable STAR Gradiometer was designed and constructed at NSWC PCD to provide a completely portable and user-friendly technology for real-time DLC of magnetic UXO. The prototype STAR Sensor comprises: a) A cubic array of eight fluxgate magnetometers, b) A 24-channel data acquisition/signal processing system. In field tests the man-portable sensor has demonstrated very robust, motion-noise-resistant DLC performance against isolated dipole type targets . This paper describes work that is ongoing to enhance the performance of the MagSTAR Technology. In particular, two improved algorithms for solving the "STAR Equations" are described: 1) A directional derivative (DD) method based on the fact that the gradient of a central potential field is a vector that points toward the target/source of the locally strongest gradient. 2) A least-squares-fit (LSF) method that iteratively calculates a magnetic target's location and magnetic signature. The DD method is being developed for better discrimination between multiple targets but for isolated targets it is more susceptible to sensor noise than the LSF method. The initial LSF method applies primarily to DLC of isolated dipole targets. Thus, the methods preferably should be used concurrently as complementary DLC modalities in environments that may be magnetically complex. These improved methods should help facilitate the transition of the STAR Technology from man-portable applications to applications using highly maneuverable autonomous sensing platforms for real-time "on the fly" DLC of magnetic targets such as UXO and buried mines.