South Carolina Aeromagnetic Compilation
Aeromagnetic anomalies are due to variations in the Earth's magnetic field caused by the uneven distribution of magnetic minerals (primarily magnetite) in the rocks that make up the upper part of the Earth's crust. The features and patterns of the aeromagnetic anomalies can be used to delineate details of subsurface geology including the locations of buried faults, magnetite-bearing rocks, and the thickness of surficial sedimentary rocks (which are generally non-magnetic). This information is valuable for mineral exploration, geologic mapping, and environmental studies.
Aeromagnetic maps of South Carolina were published in color by Zietz and others (1982) at a scale of 1:1,000,000 and black and white at 1:250,000 by Zietz and others (1983). Both maps were compiled using analog methods. To produce the analog maps, aeromagnetic contours were manually traced off a source map for each survey and combined, after photo-reduction and adjustment for level differences. The compilation of magnetic surveys in the present report uses the same aeromagnetic surveys, but combines the data digitally. The advantage of the digital product is not only the increased accuracy of the product, but also, being digital, can be plotted at a variety of scales, projections, enhancements, and is available for digital analytical tools favorable for interpretation of the data.
The digital South Carolina aeromagnetic map is constructed by combining grids of 11 separate aeromagnetic surveys flown between 1958 and 1978 (see data processing details). The data from these surveys are of varying quality. The design and specifications (flight-line separation, flight direction, analog/digital recording, navigation, and reduction procedures) varied from survey to survey depending on the purpose of the project and the technology at that time. Most were flown at 500 ft above ground and at one-mile flight line separation. An index plot and data table gives an overview and summary of survey specifications. All surveys have been continued to 1000 feet (305 m) above ground and the surveys were blended or merged together. The resulting grid has a data interval of 400 m and can be downloaded.
This grid is an interim product. Considerable editing of digital flight-line data was undertaken for two surveys (307 and 3035). Heavy strike filtering in the direction of the flight-lines was necessary to reduce flight-line anomalies for these surveys. Poor anomaly resolution can only be rectified by new surveys with more closely-spaced flight lines. Other errors may also be eliminated by new surveys with better navigation control.
This project was supported by the Mineral Resource and Geologic Mapping Programs of the USGS. Thanks to USGS colleague Pat Hill for assistance in preparing this report.
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