New Mexico Aeromagnetic Data
Processing
The assembly of 58 individual aeromagnetic surveys and grids
to create the New Mexico state-wide compilation was done in several
steps.
DATA PROCESSING STEPS
The following procedures were conducted using the commercial software package
Geosoft / Oasis montaj. References listed are those known to be used as part of the package.
- Grids were constructed from the original aeromagnetic
survey data with a cell size of between 1/3 and 1/5 of
the flightline spacing of the survey using a minimum
curvature gridding algorithm (Webring, 1982). For digitized contour line
data, the initial grid was constructed using a minimum
curvature algorithm and a spacing appropriate for the
scale of the digitized map.
- The Definitive Geomagnetic Reference Field (DGRF)
calculated for the date of the original survey was removed (in some cases this required the determination
and addition of the original reference field removed before removal of
the DGRF) .
- The original survey grids were continued to 304.8 meters (1000 feet)
above ground by converting to draped as
necessary. Upward continuation of the NURE and digitized draped surveys was by
standard 2D FFT filtering techniques. Level-to-drape continuation and
surface-to-drape continuation where true measurement elevations were known,
were performed using the chessboard method
(Cordell and others,1992).
- The survey grids were regridded, as necessary, to the
final grid cell size of 500 meters using a minimum curvature
algorithm.
- The datum levels of the converted grids were adjusted (by
addition or subtraction of a constant value) to minimize
differences at the boundaries.
- These adjusted grids were combined into a single merged grid that shows the magnetic field measured
or calculated at 304.8 meters (1000 feet) above ground. This level was selected in order to be
compatible with recent
USGS state compilations including adjacent state compilations in Utah
(Bankey and others, 1998) and Colorado
(Oshetski and Kucks, 2000).
GRID PROJECTION SPECIFICATIONS
- Projection = Lambert conformal conic
- Central meridian = 106 degrees W
- Base latitude = 32 degrees N
- Standard parallels = 33 and 45 degrees N
- Semi-major ellipsoid axis = 6378206.4 m
- Eccentricity squared = 0.0067686579973
- Horizontal Datum = NAD27
- Ellipsoid = Clarke 1866
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