Changes

The airborne magnetometer measures the total intensity of the earth's magnetic field. Modern instruments have a sensitivity of 0.01 gammas (or 0.01 nT). Gradients of the field are sometimes measured as well. Data are recorded by flying along a set of parallel lines that have perpendicular control lines to tie them together. Over smooth terrain, the magnetometer can be flown as low as [[length::100 ft]] above the earth's surface, but heights of 500 to [[depth::1500 ft]] are more typical. The line spacing for complete detail should not be much greater than the depth of the anomaly sources that are the survey target. The data are usually processed to produce total intensity contour maps (with intervals down to 1 gamma and occasionally less) and digital data files. The processing often includes calculation of the vertical gradient or second vertical derivative of the total intensity, which sharpen and emphasize local anomalies. In middle latitudes, reduction to the pole can make anomalies appear as if measured in a vertical instead of an inclined magnetic field. Filtering techniques are applied to separate anomalies of different wavelengths. Depths of anomaly sources can be calculated using a variety of model shapes, usually working with individual profiles. Finally, the interpreter determines the most probable geological anomaly sources in terms of their boundaries, size, shape, depth, and magnetization and assembles a coherent geological whole.

The airborne magnetometer measures the total intensity of the earth's magnetic field. Modern instruments have a sensitivity of 0.01 gammas (or 0.01 nT). Gradients of the field are sometimes measured as well. Data are recorded by flying along a set of parallel lines that have perpendicular control lines to tie them together. Over smooth terrain, the magnetometer can be flown as low as [[length::100 ft]] above the earth's surface, but heights of 500 to [[depth::1500 ft]] are more typical. The line spacing for complete detail should not be much greater than the depth of the anomaly sources that are the survey target. The data are usually processed to produce total intensity contour maps (with intervals down to 1 gamma and occasionally less) and digital data files. The processing often includes calculation of the vertical gradient or second vertical derivative of the total intensity, which sharpen and emphasize local anomalies. In middle latitudes, reduction to the pole can make anomalies appear as if measured in a vertical instead of an inclined magnetic field. Filtering techniques are applied to separate anomalies of different wavelengths. Depths of anomaly sources can be calculated using a variety of model shapes, usually working with individual profiles. Finally, the interpreter determines the most probable geological anomaly sources in terms of their boundaries, size, shape, depth, and magnetization and assembles a coherent geological whole.

During the past 50 years, most of the earth's land surface has been surveyed by aeromagnetics with varying detail, and a high proportion of the results have been published. Airborne and marine surveys of the oceans are less complete, but have provided the basis for studies of oceanic crust and continental drift. A sampling of regional magnetic studies has been presented by Hinze<ref name=pt07r20>Hinze, W. J., ed., 1985, The utility of regional gravity and magnetic anomaly maps: Society of Exploration Geophysicists, 454 p.</ref>, and publication of the magnetic anomaly map of North America (Committee for the <ref name=pt07r8>Committee for the Magnetic Anomaly Map of North America, 1987, Magnetic anomaly map of North America: Boulder, CO, Geological Society of America, 4 sheets, scale 1:5,000,000.</ref> showed results on a continental scale. Paterson and Reeves<ref name=pt07r47>Paterson, N. R., Reeves, C. V., 1985, Applications of gravity and magnetic surveys—The state of the art in 1985: Geophysics, v. 50, p. 2558–2594., 10., 1190/1., 1441884</ref> have reviewed the state of the art in magnetics.

During the past 50 years, most of the earth's land surface has been surveyed by aeromagnetics with varying detail, and a high proportion of the results have been published. Airborne and marine surveys of the oceans are less complete, but have provided the basis for studies of oceanic crust and continental drift. A sampling of regional magnetic studies has been presented by Hinze,<ref name=pt07r20>Hinze, W. J., ed., 1985, The utility of regional gravity and magnetic anomaly maps: Society of Exploration Geophysicists, 454 p.</ref> and publication of the magnetic anomaly map of North America<ref name=pt07r8>Committee for the Magnetic Anomaly Map of North America, 1987, Magnetic anomaly map of North America: Boulder, CO, Geological Society of America, 4 sheets, scale 1:5,000,000.</ref> showed results on a continental scale. Paterson and Reeves<ref name=pt07r47>Paterson, N. R., Reeves, C. V., 1985, Applications of gravity and magnetic surveys—The state of the art in 1985: Geophysics, v. 50, p. 2558–2594., 10., 1190/1., 1441884</ref> have reviewed the state of the art in magnetics.

==Applications==

==Applications==