9. Magnetic Exploration Methods

Abstract

The magnetic method, perhaps the oldest of geophysical exploration techniques, blossomed after the advent of airborne surveys in World War II. With improvements in instrumentation, navigation, and platform compensation, it is now possible to map the entire crustal section at a variety of scales, from strongly magnetic basement at regional scale to weakly magnetic sedimentary contacts at local scale. Methods of data filtering, display, and interpretation have also advanced, especially with the availability of low-cost, high-performance personal computers and color raster graphics. The magnetic method is the primary explo-ration tool in the search for minerals. In other arenas, the magnetic method has evolved from its sole use for mapping basement structure to include a wide range of new applications, such as locating intrasedimentary faults, defining subtle lithologic contacts, mapping salt domes in weakly magnetic sediments, and better defining targets through 3D inversion. These new applications have increased the method's utility in all realms of exploration -in the search for minerals, oil and gas, geothermal resources, and groundwater, and for a variety of other purposes such as natural hazards assessment, mapping impact structures, and engineering and environmental studies.

Superconducting sensors and methods in geophysical applications

“…pipeline and unexploded ordinance detection), and for mapping of archaeological sites. As a consequence, a wide range of reviews and more detailed articles considering instrumentation, data acquisition and processing as well as interpretation [1,6,[47][48][49] is available to the interested reader. Section 4.2.4 onward will highlight successful case stories undertaken with SQUID based instruments for magnetic prospecting.…”

“…A variety of underlying physical effects or laws [3] exist which enable to build magnetometers. There exists a number of reviews which present the evolution of magnetometers from the early days [4,5], within the past two decades [6] up to more recent developments such as [7].…”

Sources of heading errors in optically pumped magnetometers operated in the Earth's magnetic field

“…This so-called heading error [1,14] leads to certain requirements for the operation of OPMs when used for geomagnetic surveys. For example, their orientation concerning the Earth's magnetic field has to be fixed during the measurement to avoid measurement errors [15,16]. Therefore, the study of orientation effects is an important step in the development of new detection concepts with atomic magnetometers and attracts increasing scientific interest [17][18][19][20].…”

Performance analysis of an optically pumped magnetometer in Earth’s magnetic field

“…Because the energy shift by the Zeeman interaction is based on the scalar product of the measured external magnetic field B 0 and the magnetic moment of the atom, such a magnetometer measures the absolute value of the field. This fact makes them interesting for the realization of absolute field sensors [2][3][4].…”