Aerial Magnetic Surveying

the investigation of the earth’s magnetic field from an aircraft using aerial magnetometers. Aerial magnetic surveying was proposed and utilized by the Soviet scientist A. A. Logachev (1936) in the search for strongly magnetic iron ore detectable by magnetic anomalies above the deposits. (The Sokolovsko-Sarbaiskoe iron ore deposits in Kazakhstan and the Angaro-Ilimsk in Siberia were discovered in this way.) With the development of new high-precision aerial magnetometers, aerial magnetic surveying became one of the methods of regional geodesic investigation. The results of aerial magnetic surveying have been used in the compilation of geological maps, the more exact definition of the contours of geological formations, the exposure of tectonic dislocations, and so on. Large-scale aerial magnetic surveying is used in the search for iron deposits, bauxite, diamond-containing kimberlite pipes, and so on. Surveying routes are laid out parallel, perpendicular to the predominant orientation of the geological structures being studied. Aerial magnetic surveying is carried out at a constant altitude above sea level or the terrain. In the first case the flight altitude is controlled by a barometric altimeter; in the second, by an airborne radio altimeter. The geodesic correlation of routes to the terrain is accomplished using photographs from separate orienting points, and in their absence by means of radio navigational systems. For the calculation and elimination of geomagnetic field variations, the records of magnetic observatories and field variation stations, which are set up in regions of operation, are used. Sometimes variations are automatically introduced into aerial magnetometer readings by means of signals which are transmitted by radio from a ground variation station. For the coordination of the magnetic field maps of individual territories in the USSR, a single reference network has been created in terms of absolute values of the geomagnetic field. New perspectives have opened up in aerial magnetic surveying in connection with the development of quantum magnetometers having high resolving power.