Patent ID: 7403014

Claim:
In a system in which a boring tool moves through the ground in a region which includes a static magnetic field such that the boring tool is exposed to the static magnetic field and which region includes at least one electrically conductive in-ground line, an apparatus comprising: a transmitter for generating a time varying magnetic signal from an underground length of said line; a receiver carried by said boring tool for detecting a composite magnetic signal having (i) a static portion that is responsive to said static magnetic field and (ii) a time varying portion that is responsive to said time varying magnetic signal; and a processing arrangement that is configured for using information that is determinative of an instantaneous orientation of the boring tool for filtering the composite magnetic signal to obtain a first component relating to the static magnetic field and a second component relating to the time varying magnetic signal and using the first, static magnetic field component to determine a heading of the boring tool and using the second, time varying magnetic component to determine a proximity of the boring tool to the line.