| 摘要 |
The invention relates to a method of determining electromagnetically the locations of electrically conductive bodies beneath the surface of the ground, wherein a primary electromagnetic field is generated with the aid of a loop through which a sinusoidal alternating current is passed. The loop is placed at or above the level of the ground beneath which the locations of conductive bodies shall be determined. There are generated in the conductive bodies currents which, in turn, generate a secondary electromagnetic field, wherein the values of the amplitude and phase of the magnetic component of the thus formed total electromagnetic field are measured in three linear independent directions with the aid of coils mounted inside a probe which is lowered to different depths in a borehole which extends down into the ground within the propagation area of the primary field. The measured values are transmitted through a transmission line to a receiver, as are also the values for determining the phase of the primary field, so as to enable the phase difference between the primary field and the total field to be calculated. This difference is used to determine the three real and three imaginary components of the secondary field, these components in turn being used to determine the location of the conductive bodies. The invention is characterized in that the values of the primary field phase are measured continuously by at least one reference coil which is placed outside the probe, either above or beneath the surface of the ground, within the propagation area of the primary field. the reference coil is orientated so as to receive at least one component of the magnetic field and the signals obtained from the reference coil, or the result of processed signals, are transmitted to the receiver on a transmission line.
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