A human-portable utility locator system for locating and tracing a buried
utility line characterized by an electromagnetic field emission. The
locator may include a horizontal spaced sensor pair for detecting the
horizontal field asymmetry of the emitted field in one or more
independent frequency bands, which is employed to assist in determining
an accurate "virtual depth" measurement for producing detection events.
An event detector may be disposed to detect events corresponding to
extremum in the B-field gradient with respect to time and a user
interface (UI) coupled to the event detector signals the detected event
to a user. In a preferred embodiment, one pair of spaced-apart 3D
magnetic sensor arrays is disposed substantially orthogonal to another
intermediate spaced-apart pair of sensors.