Arizona 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.
The Arizona aeromagnetic map is constructed from grids that combine information (see data processing details) collected in 43 separate aeromagnetic surveys conducted between 1947 and 1999. The data from these surveys are of varying quality. The design and specifications (terrain clearance, sampling rates, line spacing, and reduction procedures) varied from survey to survey depending on the purpose of the project and the technology of that time. Every attempt was made to acquire the data in digital form. Most of the available digital data were obtained from aeromagnetic surveys flown by the U.S. Geological Survey (USGS), flown on contract with the USGS, or were obtained from other federal agencies and state universities. Much of the pre-1980 data are available only on hand-contoured maps and had to be digitized. These maps were digitized along flight-line/contour-line intersections, which is considered to be the most accurate method of recovering the original data. Digitized data are available as USGS Open File Report 99-557. All surveys have been continued to 304.8 meters (1000 feet) above ground and then blended or merged together. An index plot gives an overview of the original surveys, and a data table summarizes the detailed specifications of the surveys. The map can be downloaded as a grid with a 500 meter grid interval.
Also included are maps and grids of some of the individual surveys at their original flight elevation that were generated with a finer grid spacing due to a finer flight line spacing. These were then regridded to the final grid spacing of 500 meters for use in the state merge.
Our priority in the construction of the state of Arizona aeromagnetic compilation was always to acquire the best resolution aeromagnetic data sets for any given area. (See the Arizona aeromagnetic data index map.) Where local high-resolution surveys were not available, in either digital or digitized format, we used aeromagnetic data collected by the University of Arizona (Sauck and Sumner, 1970) and by the National Uranium Resource Evaluation (NURE) program of the U.S. Department of Energy, which are both available in digital format and together cover the entire state. It is important to note that, because of the design of the flight specifications for these University of Arizona and NURE surveys, their data are subject to certain limitations. The University of Arizona data were collected in 2 surveys flown at 2740 meters (9000 feet) and 3350 meters (11000 feet) barometric elevations, both at flight line spacings of 4800 meters (3 miles). Although the NURE surveys were flown at elevations 122 meters (400 feet) above ground, and closer to the reduction datum level, the maximum spacing between flight lines was also 4800 meters (3 miles). This spacing between flight lines flown at low altitudes over surface rock units having high magnetizations causes anomalies with short spacial wavelengths to be elongated between flight lines, producing lineations perpendicular to the flight-line direction and 'pearl string' anomalies along the flight line. Also, problems related to the reduction of navigation control and inconsistent datum levels between NURE surveys can cause herringbone features which are sometimes observed within and at the boundaries of these surveys.
This project was supported by the Mineral Resource Program/Crustal Imaging and Characterization Team of the USGS. The authors wish to thank our USGS colleagues for their assistance in preparing this report, Mark Gettings for providing the gravity data base used in this report, and Jeffrey Phillips, Mike Webring, and Bob Kucks for the in-house software used to prepare the aeromagnetic data.
The USGS also acknowledges the U.S. Bureau of Indian Affairs Division of Energy and Minerals for funding the San Carlos aeromagnetic survey used in this report.
U.S. Department of the Interior
U.S. Geological Survey
This page is <URL: https://greenwood.cr.usgs.gov/pub/open-file-reports/ofr-01-0081/html/arizona.htm>
Maintained by: Gene Ellis
Last Modified Monday, 15-May-2000
For more information about this report contact: Ron Sweeney
