Air-Borne Magnetometers for Search and Survey

Air-borne magnetometers developed during the war for the detection of submerged enemy submarines now have become important tools for aerial geophysical exploration. The instruments described utilize the second harmonic outputs produced by the magnetic field in saturated core inductors for field measurement and for control of servo stabilizing systems acting around two axes to maintain the measuring element in alignment with the earth´s field. The field to be measured is compared continuously with that produced in the measuring inductor, winding by an accurately controlled direct current. The sensitive element usually is towed in a bombshaped bird sufficiently removed from the airplane to escape the effects of its magnetic field. A continuous record is produced which, when keyed with position records obtained by photography or shoran, may be used in the preparation of maps of total magnetic field intensity.