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

Abstract

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.

Detection of a perfect conductor with an airborne electromagnetic system: The Gemini Field Test

“…Shown is the analysis for a coplanar system, basically an airborne Slingram geometry. At the typical fixed-wing Tx-Rx separations around 100 m, accuracies in the range of a few cm are required, consistent with Hefford et al (2006). However, at 400-m separation, 1 m of relative geometrical error would be adequate for primary field calculation even with depths of up to 300 m for the small target.…”

The mutual inductance calculation between circular and quadrilateral coils at arbitrary attitudes using a rotation matrix for airborne transient electromagnetic systems

“…According to the measured attitudes of the transmitting coils of the ATEM systems provided by the papers of Hefford et al (2006) and Yin and Fraser (2004), we simulated the numerical curves of varying attitudes of transmitting coils. The results are shown in Fig.…”

“…However, it is common to measure the attitude variations of ATEM systems directly or indirectly by installing an inertial navigation system or two laser altimeters, differential Global Position System (GPS) devices and inclinometers (Gunnink et al, 2012;Hefford et al, 2006;Smith, 2001), and then we can use the Neumann mutual inductance formula and the measured attitude variations to transform the coordinates of circular coils or polygonal coils at arbitrary attitudes with a rotation matrix. Thus the singular values of two vertical coils can be calculated as well as the mutual inductance of polygonal and circular coils at arbitrary attitudes and arbitrary positions.…”

Metalliferous mining geophysics — State of the art after a decade in the new millennium

“…If this is straightforward and provides a significant benefit, it could be adopted for use in the airborne EM systems used in the mineral exploration industry. If the position is being used to estimate the in-phase response of highly conductive (nickel) bodies, extremely accurate estimates are required (Smith, 2001a;Hefford et al, 2006). Similar work on monitoring system geometry was undertaken for frequency-domain systems.…”