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Quantifying the Effects That Changes in Transmitter-Receiver Geometry Have on the Capability of an Airborne Electromagnetic Survey System to Detect Good Conductors

¹ Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6,
² Fugro Airborne Surveys, 2060 Walkley Road, Ottawa, Ontario K1G 3P5.

Time-domain electromagnetic systems are most sensitive to highly conductive targets during the transmitter on-time. Data collected during the on-time is highly influenced by the geometric relationship between the transmitter and the receiver. Unless corrections can be applied for these geometric variations, the ability to correctly detect and identify highly conductive targets can not be fully realized.

Variables affecting the relative position between the transmitter and receiver include changes in the position of the receiver with respect to the transmitter, variations in transmitter attitude, and transmitter loop deformation. The level of accuracy in the determination of the relative geometry required to permit complete removal of the effects due to geometric variations is different for each of the variables and is dependent on the depth of the target. The most influential geometric variation involves changes in the relative position of the receiver with respect to the transmitter along the direction of flight; this variable, therefore, requires the highest degree of accuracy. The accuracy required for receiver motions along the vertical direction is roughly one order of magnitude less, and in the lateral direction, several orders of magnitude less.

The objective of this paper is to relate the sensitivity of the response to transmitter-receiver geometry to the ability of an airborne, time-domain electromagnetic system to resolve a highly conductive vertical target. This is achieved by a detailed analysis of the effect of the individual x, y, and z distances between the transmitter and the receiver, the transmitter attitude (roll, pitch, and yaw), and transmitter deformation.

Key Words: Exploration geophysics • Electromagnetic methods • Airborne surveying • Transmitter-receiver geometry • Conductive target detection • Aircraft attitude • Transmitter loop deformation