Generalized Magnetic Gradient Contraction Based Method for Detection, Localization and Discrimination of Underwater Mines and Unexploded Ordnance

Abstract

We report significant progress toward full development of a unique magnetic-gradienttensor-based "Scalar Triangulation and Ranging (STAR)" method for detection, localization and classification (DLC) of magnetic targets. The STAR method converts magnetic tensors to rotationally invariant scalar parameters that are virtually unaffected by the effects of sensing platform motion. Thus, the STAR method is particularly appropriate for magnetic target DLC using highly mobile sensing platforms such as Autonomous Underwater Vehicles (AUV). Prior work has resulted in development of a twodimensional (2-D) magnetic target-homing concept for fully autonomous localization of mines using crawler-type AUVs. However, the simple 2-D STAR approach cannot effectively discriminate between magnetic clutter and mine-like target signatures.Improved, 3-D simulations demonstrate that the STAR concept can be applied to measurements of the vector positions and dipole signatures of magnetic objects. The new results indicate that an improved STAR system will provide an enhanced capability for discrimination between magnetic clutter and real targets such as magnetic mines and Unexploded Ordnance (UXO).Consequently, further development of the advanced STAR concept will provide high-mobility autonomous sensing platforms (such as AUVs and man-portable systems) with a uniquely effective modality for DLC of magnetic mines and UXO.

Magnetic STAR technology for real-time localization and classification of unexploded ordnance and buried mines

“…References [1][2][3] provide detailed descriptions of the basic STAR concept and the construction of the prototype manportable MagSTAR sensor. For convenience, the following paragraphs present a summary of STAR theory, the manportable sensor's construction and its operation.…”

“…b) The triangulation baselines, their respective end-point C T values and Eq. (4) can be used in a STAR algorithm [1,2] to determine components of target location vector r. c) Substitution of r-components into gradient equations Eq. (2) yields an approximation to the vector components of M that are so important for UXO discrimination and clutter rejection [6,7].…”

“…Vector B-field data from the sensors in the six faces of the cube are used to generate a set of six C T -parameters. The distances (30 cm) between faces of the cube constitute "triangulation baselines" for target-ranging using a scalar triangulation scheme [1][2][3][4][5]. • A Sensor Support Structure composed of extremely rigid and lightweight carbon fiber composite supports the TFMs and maintains their alignment in the cubic array.…”

“…The new technology is based on a Magnetic "Scalar Triangulation and Ranging (MagSTAR)" concept that was created to enable faster and more effective magnetic sensing of UXO and buried mines [1]. Proof of principle of the concept has been demonstrated by a prototype man-portable MagSTAR sensor that was constructed and field-tested at Naval Surface Warfare Center Panama City Division (NSWC PCD) [1][2][3][4][5]. Currently, the STAR project's R&D effort is focusing on development of improved signal processing algorithms for optimization of the technology's accuracy, range and ability to discriminate between magnetic UXO and clutter.…”

“…The prototype man-portable MagSTAR has clearly demonstrated a unique and valuable motion-noise-resistant capability for real-time, point-by-point DLC of magnetic targets using highly mobile sensing platforms [3][4][5] . However, the basic STAR localization and classification process is subject to "asphericity errors" that can result in significant inaccuracies in the MagSTAR's measurements of location r and magnetic signature M [1]. Since accurate knowledge of location and magnetic signature of UXO can be critically important for the safety and efficacy of a real-world DLC application recent R&D work on the MagSTAR technology has focused on the development of new and improved signal processing algorithms for enhancement of the accuracy of the technology's measurements of r and M.…”