Abstract: Ferromagnetic material of an elongated object, such as a fiber optic cable, is permanently magnetized in a manner that results in a substantially cylindrically symmetric radial external magnetic field around the object. The produced magnetization is substantially greater than natural magnetization of the ferromagnetic material by the earth's magnetic field. The radial external magnetic field varies periodically along the length of the object. If the wavelength of the periodic variations is long compared to the width (diameter) of the object, the strength of the radial external magnetic field decreases approximately inversely with distance from the object for distances that are small compared to the wavelength. The periodic magnetic field variations may have a square wave or a sine wave pattern, for example.

Abstract: Ferromagnetic material of an elongated object, such as a fiber optic cable, is permanently magnetized in a manner that results in a substantially cylindrically symmetric radial external magnetic field around the object. The produced magnetization is substantially greater than natural magnetization of the ferromagnetic material by the earth's magnetic field. The radial external magnetic field varies periodically along the length of the object. If the wavelength of the periodic variations is long compared to the width (diameter) of the object, the strength of the radial external magnetic field decreases approximately inversely with distance from the object for distances that are small compared to the wavelength. The periodic magnetic field variations may have a square wave or a sine wave pattern, for example.

Abstract: At least one pair of vector gradiometers is employed to locate (and track) magnetic objects or sources. A first signal, S, is produced as a function of the difference in the absolute values of output signals L and R from left and right gradiometers, respectively. The form of the signal depends upon whether the magnetic field associated with the object or source is symmetric or anti-symmetric and is selected in accordance with observations made as the gradiometer pair passes over the magnetic object or source. A second signal, V, is produced as a function of the sum of the absolute values of signals L and R and represents total strength. A third signal, H=S/V, is produced to determine whether the observer is to the left or to the right of the magnetic object or source and is independent of the magnetic field strength and polarity of the magnetic field, even where the polarity and magnetic field strength vary with distance along a linear source.