The aeromagnetic method of geophysical surveying has been established in less than two decades as a powerful method in mining and petroleum exploration. Many economically important discoveries can either directly or indirectly be credited to the aeromagnetometer. Magnetic methods are most important in their assistance to geological reconnaissance and mapping. Also, deep crustal and upper‐mantle studies can be made from results. New instruments, the spin‐precession magnetometers, have come into being in the past five years. Included are the proton‐precession magnetometer, the alkali‐vapor rubidium and cesium instruments, and the metastable‐helium magnetometer. All of these devices have airborne capabilities, and their future use is destined to increase. Modern navigational and interpretational techniques have improved the usefulness of aeromagnetic surveying. Diurnal effects are corrected for and their behavior is becoming understood. Data compilation, the major step in the entire process between measurement and interpretation, is an involved routine, but can be automated with the aid of Doppler navigation and statistical techniques. Interpretative systems may be divided into qualitative inspection, profile analysis, and map methods. Numerous schemes have been proposed for analytic purposes and the principal methods are reviewed. Although much of the world has been covered by surveys, the program seems less than half done. With more emphasis on detailed surveys, comprehensive interpretation, and sensitive instruments, the future of aeromagnetics seems bright.

In comparing the similarity between time, frequency, and phase measurements as used in the induced polarization method of geophysical prospecting, parameters must first be defined and the basis for comparison established. The conditions for mathematical equivalence then follow in a natural sequence. Laboratory measurements are made on a variety of rock samples to indicate the type of comparison and correlation expected from field measurements. Results indicate that frequency domain and phase measurements are equivalent, but two frequency domain measurements are needed to produce the same amount of polarization information as a single phase measurement. Frequency and time domain measurements will be similar but never equivalent due to the basic differences in their respective parameter definitions.

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