Geophysical exploration involves the measurement, at the surface of the Earth, of physical quantities which will provide information about the structural configuration of the Earth's crust. Geophysical surveys are made for petroleum and mining companies to discover subsurface structures favourable to the accumulation of minerals of economic significance.

When geophysical exploration was extended to sea, pinpoint marine navigation became a requirement so that the prospector could return to the exact site of the geophysical anomaly. At first, operations were so near the shore that position determination was no problem. Visual observations were quite adequate. As operations pushed farther from land, high-accuracy electronic systems were pressed into service. Such names as Decca, Lorac, Raydist, and Shoran are familiar in the oil industry. But when operations extended beyond the range of precision radio systems and into areas where they were neither available nor could readily be made available because of hostile terrain, natives, or politicians, or where adequate surveys of shore transmitting stations were impractical, other means of navigation were needed. Navigation satellites, used in conjunction with other navigation equipment, fulfil this need.