U.S. Geological Survey

Utah Aeromagnetic Data Processing

The assembly of 20 individual aeromagnetic surveys and grids to create the Utah state-wide compilation was done in several steps.


  1. 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. 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.
  2. The Definitive Geomagnetic Reference Field (DGRF) calculated for the date of the original survey was applied (in some cases this required the determination and removal of the original reference field applied).
  3. The survey grids were regridded, as necessary, to the final grid cell size of 1000 m using a minimum curvature algorithm.
  4. To create the composite aeromagnetic grid, the datum levels of adjacent surveys were adjusted (by addition or subtraction of a constant value) to minimize differences at the boundaries.
  5. The original survey grids were upward continued to 12,500 ft barometric elevation and converted from drape to level as necessary. Upward continuation of the NURE surveys was by standard 2D FFT filtering techniques. Level-to-drape continuation was performed using the method described in Cordell and others, 1992).
  6. The datum levels of the converted grids were adjusted to minimize differences at the boundaries.
  7. These adjusted grids were combined into a single merged grid that shows the magnetic field measured or calculated at 12,500 ft barometric elevation.
  8. Two regional aeromagnetic lines flown by the Navy's Project Magnet (one east-west at approximately 38.5 degrees and one north-south at -112.3 degrees) and one long NURE line (east-west at 39.5 degrees) were used to check for datum shifts across the merged map, using the method by Grauch (1993). Profiles were extracted from the merged data along these three lines and compared to the regional anomalies to search for datum shifts between surveys. These shifts result from removing incorrect constants before merging. Where line comparisions show a datum shift, the correct constant was removed, even though in some places this resulted in visible merge boundaries. These lines directly crossed parts of surveys A, B, H, I, J, L, M, N, O, and Q.
  9. Conversion of the merged grid from level to draped surface was performed using two different methods: chessboard (Cordell and others, 1992) and xia-m (Phillips, 1996).


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