The depth and lateral offset position of an underground pipeline or the like is calculated by a surface located instrument carrying two spaced sets of orthogonal antennas sensing electromagnetic energy induced in and radiated from the pipeline. The resulting four signals are compared in amplitude to derive by simple triangulation calculations the depth and offset distances in a simple computer-display unit. Thus a set of continuous reading may be made automatically by a self-contained portable unit as an operator tracks the pipeline to make a survey. The readings may be recorded upon a medium advanced by a measuring instrument as a survey progresses along a pipeline.
Glenn T. Darilek; Edward H. Cooper