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Aeromagnetic Regional Grid Data
Several regions are represented in this unique collection of earth surface measurements of magnetic field parameters and their related anomalies. The DNAG Magnetics "Super grid" of Magnetic Anomaly Map of North America was created from the four "Original" DNAG Magnetic data sets distributed by The Committee for the Magnetic Anomaly Map of North America, 1987. This development of a super grid involved an extensive task of matching original quadrant information and eliminating overlap. The resulting grid, with x and y step intervals of 2.0 kilometers yields a grid with dimensions (4451 x 4273) containing 19,019,123 values. This process can be thought of as "stitching the grids." The data in this grid are in a Spherical Transverse Mercator projection, the kilometer coordinates of which can be recovered from the indices of a grid point. The Ministry of Geology of the USSR published a mosaic series of 18 maps in 1974, at a scale of 1:2,500,000 showing the residual magnetic intensity over the land mass of the USSR. Much of the source material originated from data collected between 1949-1962, during which time the entire territory of the USSR was surveyed using aerial magnetic survey techniques. These surveys wereadjusted based on many methods including secular variation linked to magnetic observatories. Anomalies were computed with reference to a normal field map for 1964-65 constructed from equally accurate total field measurements along control network strips. Digitization was accomplished in 1982 by the U.S. Naval Oceanographic Office. The "BRIGGS cubic spline" method was used to compute grid values. A one-minute grid was created by properly matching the boundaries of the digitized sub-sections. The units of the original map aremilli-Oersteds and the units of the resulting digital grid are milli-Oersted/100. Corrections to the digital contour file were made by Conoco 1993. New Grid files at 2.5 Km and 5.0 Km spacing were created and re-archived by NGDC. These data are available on CD-ROM. World Data Center-A (WDC-A) for Solid Earth Geophysics presently holds Grid data from many U.S. and other regions. These data were contributed by: USGS, MINN G.S. and other Worldwide organizations. Grid intervals vary but are as fine as 213.36m for the NGS Super Grid of the state of Minnesota. Other grids were recreated indigital form from previously published maps and charts. The bulk of these grid data files were contributed to NGDC after 1985. A detailed list of the specific regions is available upon request.