Enhanced UXO Discrimination Using Frequency-Domain Electromagnetic Induction

Abstract : The Chemistry Division of the Naval Research Laboratory has participated in several programs funded by SERDP and ESTCP whose goal is to enhance the discrimination ability of MTADS. The process is based on making use of both the location information inherent in an item s magnetometry response and the shape and size information inherent in the response to the time domain electromagnetic induction (EMI) sensors that are part of the baseline MTADS in either a cooperative or joint inversion. In all these efforts, our classification ability has been limited by the information available from the EMI sensor. The EM61 is a time-domain instrument with either a single gate to sample the amplitude of the decaying signal or four gates relatively early in time. To make further progress on UXO classification, a sensor with more information available is required. The GEM-3 sensor is a frequency-domain sensor with up to ten frequencies available for simultaneous measurement of the in-phase and quadrature response of the target. Thus, in principle, there is much more information available from a GEM-3 sensor for use in classification decisions. Unfortunately, the commercial GEM sensor is a hand-held instrument with relatively slow data rates and is thus not very amenable to rapid, wide area surveys. ESTCP Project 200033, Enhanced UXO Discrimination Using Frequency-Domain Electromagnetic Induction, has been funded to overcome this limitation by integrating an array of GEM sensors with the MTADS platform. The objective of this program was to demonstrate the optimum system that delivers the most classification performance while retaining acceptable survey efficiency. Working around a modified GEM-3 sensor (modified based on our observations during an initial, sensor characterization phase of the program), we have designed a three-sensor array and demonstrated it at the Standardized UXO Demonstration sites at Aberdeen Proving Ground and Yuma Proving Ground.