GB1351912A - Method and device for determining the depth of a magnetic anomaly - Google Patents

Abstract

1351912 Magnetic surveying COMMISSARIAT A L'ENERGIE ATOMIQUE 12 June 1972 [16 June 1971] 27287/72 Heading G1N In aerial magnetic survey, the depth Zo of a submerged magnetic anomaly at least approximately comparable with a horizontal dipole (e.g. a submarine) is deduced by determining the variation in the perturbation H to the Earth's magnetic field caused by the anomaly and the variation in the gradient -#H/#u a long a horizontal path perpendicular or parallel to the dipole and calculating Zo using the formula where m = 1 if the path is parallel to the dipole or 1/3À5 if perpendicular. The path may be a circle centred at the origin of the anomaly or in the form of a fourleaved clover crossing the origin in directions parallel and perpendicular to the dipole. In Fig. 5, the output of a frequency meter 18 connected to a proton resonance magnetometer head 10 mounted in a tail extension of an aircraft is corrected for magnetic effects of the aircraft by subtracting at 20 the output of a phase meter 16 connected to a proton resonance filter 12. A bandpass filter 22 eliminates the constant components of the field so that only the perturbation H is recorded on a tape recorder 24. The output of filter 22 is sampled at 27 at regular intervals (e.g. 1 second) determined by a clock 30 and fed to a shift register 28. H max is determined by a comparison circuit 32 and (#H/#u) max is determined by a subtractor 34 and comparison circuit 36. Circuit 38 calculates Zo, using a manually set value of m. The aircraft's altitude may be fed in at 44 to be subtracted from Zo.