Decay Time Constant Analysis for Uxo Target Prioritization

The Geonics EM-61MK2 is currently used for many surveys for UXO detection. The system has<br>the capability to record the voltage over four different times after current turn off in the<br>transmitter/receiver coil. This allows the computation of the time constant of decay between these four<br>channels and the possibility that this additional information could be used to prioritize geophysical<br>anomalies for intrusive investigation. Previous work has demonstrated that the four time gates are<br>located too soon after the current turn-off to perform an inversion capable of characterizing the buried<br>objects in terms of its size, shape, depth and composition. This paper will analyze the potential for the<br>apparent time constant to prioritize the geophysical anomalies and reduce the number of anomalies that<br>are intrusively investigated, by lowering the priorities of anomalies that have clearly different<br>characteristics from the objects of interest.<br>This paper will focus on geophysical surveys conducted for the Chemical Warfare Materiel<br>(CWM) Scoping and Security Study for the purposes of detecting steel Chemical Agent Identification<br>Sets (CAIS) shipping containers. There objects are larger and heavier than typical munitions and<br>explosives of concern (MEC) items and thus offer a better opportunity to prioritize target selection.<br>Additional data from test are also discussed in this paper.