| 摘要 |
A method of detecting location of a buried magnetically-marked elongated object (12) uses a horizontal gradiometer (14) for measuring the horizontal gradient of components of a magnetic field associated with the buried object (12). The object (12) is preferably provided with a helical permanent magnet marking device (10) magnetized transverse to its length to provide magnetic field components above the surface of the earth that vary periodically along the length of the device (10). The gradiometer has horizontally spaced sensors (S) and is designed to measure variations of the horizontal gradient of a vertical magnetic field component, and to measure variations of the horizontal gradient of a horizontal axial magnetic field component, as the gradiometer (14) is moved along the surface of the earth approximately parallel to the buried permanent magnet marking device (10). The measured gradient variations may be read out individually or as a sum. The method provides improved sensitivity and selectivity, which reduces errors due to magnetic clutter. |
