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

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