| 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 Inc.in 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. |
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