Use of on-time gates to determine relative transmitter–receiver separation for transient electromagnetic systems with a single-component transmitter and receiver

ABSTRACT An approach to dynamically determine the separation between transmit and receive coils in electromagnetic systems based upon measurement of the primary field induced voltages was presented. This approach proposes an adaptation of primary-field-based localization schemes suitable for a two-horizontal-coil setup common to many ground-based or towed transient electromagnetic platforms. It was shown that the dominant influence on primary field induced voltages was radial displacements and that neglecting other tangential displacements and/or rotation effects introduced only minor offset biases in an approach that assumed a radial offset was solely responsible for the on-time voltages. Secondary fields produced by a conductive earth were shown to perturb on-time measurements during intervals of rapid current change in the transmit loop, and recommendations for reducing these influences were discussed. Field results indicated a 10 s of centimeters localization of the receiver can be achieved for offsets up to 20 m.