Patent ID: 7078905

Claim:
A system for locating a horizontal bore below a ground surface, said system comprising: a transmitting source configured to radiate from said bore a dipole magnetic field aligned with said bore; a receiver remote from said transmitting source and having a first coil and a second coil, each coil defining an axis, wherein said axes of said first coil and said second coil are orthogonal to each other; and a measurement device in communication with said coils and configured to measure a phase of signals induced on said coils by said magnetic field when said axis of said first coil is horizontally perpendicular to the axis of said magnetic field and said axis of said second coil is vertically perpendicular to said axis of said magnetic field, and determine a lateral position of said transmitting source relative to said coils responsively to said phase of said signals on said first coil and said second coil.