magnetic survey[mag′ned·ik ′sər‚vā]
systematic measurements of the components of geomagnetism and compilation of magnetic charts based on measurement data.
A distinction is made between general and detailed magnetic surveys. A general magnetic survey, which is carried out over large areas with a comparatively sparse network of measurement sites (separated by tens or hundreds of kilometers), provides for the study of the basic principles governing the distribution of the geomagnetic field. Charts compiled on the basis of a general magnetic survey are essential for maritime and air navigation, for finding significant magnetic anomalies, and for studying the secular change of the components of geomagnetism. A detailed magnetic survey with a distance of 1 m to several kilometers between measurement sites (strips) is used mainly for geological mapping and prospecting for ore deposits.
In a magnetic survey the absolute value of the vector of the total intensity of the geomagnetic field is usually measured, but for purposes of geological surveys efforts are often limited to relative determination of the vertical component of the field. A magnetic survey is carried out by various types of magnetometers carried by satellites, aircraft, nonmagnetic ships, and surface vehicles. Continuous observations of variations in the geomagnetic field over time (the secular change of the field) are made by networks of magnetic observatories.