Survey of the Earth's magnetic field, based on data from magnetometers towed behind aircraft or suspended below helicopters. These instruments measure the total intensity of the geomagnetic field or, occasionally, components of this field. The resulting measurements can then be compared with theoretical models for the value of the field and the differences (magnetic anomalies) can be interpreted in terms of changes in the magnetic properties of the rocks below the survey line or grid. The magnetometers are usually flown with other instrumentation, e.g. radiometric and electromagnetic, at the lowest practicable constant height above the ground. Usually the magnetometer is housed in a ‘bird’ towed behind the aircraft, or in a wing-tip pod, or in a ‘stinger’ in the tail. In cases where the magnetometer is on board, in-board coil systems compensate for the aircraft's own magnetic field.
Subjects: Earth Sciences and Geography.