A Standardized Excitation Approach for Classification of Buried UXO F. Shubitidze (1) , K. O’Neill (1,2) , I. Shamatava (1) , K. Sun (1) and K.D. Paulsen (1) (1) Thayer School of Engineering, Dartmouth College, Hanover NH, 03755 , USA Email: fridon.Shubitidze@dartmouth.edu (2) USA ERDC Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover NH, 03755, USA Abstract - In this paper a new discrimination procedure is presented to enhance classification of buried metallic object. This algorithm is based on a standardized source set (SSS) approximation, applicable for an arbitrary highly conducting and permeable metallic objects placed in a low frequency (from 10’s of Hertz up to several 100’s of kHz) time varying electromagnetic field. The method treats accurately all near field, heterogeneity, and internal interaction effects. In the SSS approach, any input primary magnetic field is represented as a sum of magnetic fields produced by a set of sources distributed over on an auxiliary surface outside the fictitious surface. The object’s response corresponding to unit amplitudes of any of these input field sources is likewise quantified in terms of a set of (responding) sources, which can be derived from measured data. Thereafter, the object's response to any excitation can be expressed just by different superpositions of these standardized inputs. The spatial distribution and frequency dependence features of responding equivalent sources are analyzed and used for target discrimination. The numerical results are given for an actual unexploded ordinance (UXO). 1. INTRODUCTION The detection and remediation of UXO at closed, transferred and transferring ranges have been identified as the one of the military’s most pressing environmental and military problems for many years [1].. In the United State alone more than 900 sites (about 11 million aces of land) are potentially contaminated with UXO. The estimated cost for identifying and disposing of UXO is to be as high as $500 billion in United States. This is mainly due to lack of sufficient technologies to detect all UXO that may be present at a site and the inability to discriminate between UXO and non-hazardous items. Most UXO are heterogeneous objects containing parts of different metals [2]-[4] e.g., head, body, tail and fins, copper banding, etc. Electromagnetic fields radiated by both EMI sensors and their target fall off very sharply as function of distance (~1/R 3 ), for a combined ("round trip") decay rate of ~ 1/R 6 [3]-[6]. Therefore EMI responses from buried unseen heterogeneous objects depend strongly on what parts of the target are closest to the sensor and on the the degree of coupling between different parts [3], [4]. Further, in many highly contaminated sites, multiple UXO together with widespread clutter appear simultaneously within the field of view of the sensor. This complicates UXO detection and discrimination even more. Field experience indicates that something on the order of 75 % of the costs to clean up UXO sites are currently spent on excavating targets that pose no threat. Thus, at present the major problem is discrimination not detection. Electromagnetic induction sensing (from 10’s of Hertz up to several 100’s of kHertz) has been identified as one of the most promising technologies for UXO detection and discrimination. EMI sensing is based on EM field diffusion phenomena [2]-[6]. In EMI a time varying electromagnetic field is used to illuminate a highly conducting and permeable metallic target. In general, displacement currents can be neglected in both target and surrounding ground [3]- [6]. The practical depth of penetration of EMI signals is typically not limited by lossiness of conductive ground, and signal clutter due to dielectric heterogeneity of the ground is negligible. The primary field penetrates the object at least to some extent, and induces eddy currents within it. These currents then produce a secondary EM field, which is recorded by a receiver. The characteristics of the secondary field are determined by the target geometry, its heterogeneity and electromagnetic parameters [3]-[6]. Depending on the scatterer’s electromagnetic properties, different eddy currents are induced inside different metals. These currents produce strong EM fields in nearby parts, with consequent strong couplings between objects or pieces of an object. This has been conformed numerically [3], [4] and experimentally [2]. In the UXO community, the signal processing techniques currently used to characterize buried metallic objects are based on simple models with infinitesimal, co-located or offset magnetic dipoles. These approximate the complete object’s response in both the frequency and time domains. EMI data inversion methods to discriminate between objects of interest and other non-hazardous items typically proceed by first recovering a set of parameters that specify a physics-based model of the object being interrogated. The relationship between the inverted parameters and object of