Improving Uxo Characterization Accuracy By Accounting For Sensor Position And Orientation Effects

Abstract

Detection and characterization of small subsurface targets such as unexploded ordnance (UXO) derived from analysis of electromagnetic induction (EMI) data fundamentally relies on accurate spatial registration of all collected data. The uncertainties in position and orientation of the EM source and receiver coils are the largest source of errors that affect the fidelity of the data, which, in turn, determines the accuracy and reliability of target characterization. This paper addresses the challenges of how to precisely obtain the three-dimensional sensor positioning and orientation and quantitatively discuss their influences and compensation to the observed EMI data. Three topics are explored: 1) the inadequacy of conventional Global Positioning System (GPS) technology for 3D positional data and improvements available from robotic total station (RTS) technology; 2) the systematic assessment of EMI target signature effects caused by various conditions of sensor mis-location and orientation deviations; and 3) the collection of supplemental 3-axis gyro orientation measurements (yaw, pitch and roll) and 3-axis acceleration measurements to facilitate geophysical analysis techniques that account for varying sensor orientation during data collection. Over some targets, recent controlled tests document EMI peak amplitude responses reduced by up to 30% when the sensor was tilted as little as 5 degrees. The incorporation of orientation information into EMI inversion modeling algorithms is necessary to use these parameter-based discrimination methods in order to classify targets and reduce false alarms.