U.S. Geological Survey

Arizona Aeromagnetic Data Processing

The assembly of 43 individual aeromagnetic surveys and grids to create the Arizona state-wide compilation was done in several steps, using almost exclusively both a Unix and a PC version of Geosoft/OASIS montaj. References listed below are those known to be used as part of this package. The Definitive Geomagnetic Reference Field corrections (see step 2/ below) were done with in-house software.


DATA PROCESSING 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 (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.
  2. 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) (Sweeney, 1990).
  3. Much of the data required microlevelling, using OASIS montaj, before continuation to our reference surface. This procedure uses decorrugation, and attempts to remove any artificial trends or anomalies due to residual flight line noise remaining in the data. The grids resultant from this step (whether or not microlevelling was performed) whose grid spacing is less than the final grid cell size of 500 meters for the composite grid are available for downloading, and are listed below.
  4. The original survey grids were continued to 304.8 meters (1000 feet) above ground by draping 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 the true measurement elevations were known, were performed using the chessboard method (Cordell and others, 1992).
  5. The survey grids were regridded, as necessary, to the final grid cell size of 500 meters using a minimum curvature algorithm.
  6. The datum levels of the converted grids were adjusted (by addition or subtraction of a constant value) 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  304.8 meters (1000 feet) above ground. This level was selected in order to be compatible with recent USGS state compilations, such as those in Utah (Bankey and others, 1998), Montana (McCafferty, 1998), Colorado (Oshetski and Kucks, 2000), and Wyoming (Kucks and Hill, 2000).

INTERMEDIATE GRIDS AVAILABLE FOR DOWNLOADING

  1. az1000ag - Final Arizona composite grid at 1000 ft. above ground & gridded at 500 m.
  2. ar100mag - Arivaca survey (4234) gridded at 100 m.
  3. pat50jp - Patagonia survey (4191) gridded at 50 m.
  4. tuc50mag - Tucson survey (4211) gridded at 50 m.
  5. tap100mag - Merged Arivaca-Tucson-Patagonia surveys (4234, 4211, 4191) at original flight elevations & gridded at 100 m.
  6. tap100dr750 - Merged Arivaca-Tucson-Patagonia surveys (4234, 4211, 4191) continued to 750 ft. above ground & gridded at 100 m.
  7. f0002magf - Phoenix survey (0002) gridded at 200 m.
  8. f0007magf - Jerome-Prescott survey (0007) gridded at 100 m.
  9. f0540mag - Hopi Buttes survey (0540) gridded at 200 m.
  10. f3127amagf - Silver City North survey (3127A) gridded at 250 m.
  11. f4013magf - Dragoons '80 survey (4013) gridded at 200 m.
  12. f4014mag - Buck Robinson Peak survey (4014) gridded at 200 m.
  13. f4015mag - Whetstone Mountains survey (4015) gridded at 200 m.
  14. f4016magf - Arnold Mesa survey (4016) gridded at 200 m.
  15. f4017magf - Silver City South survey (4017) gridded at 250 m.
  16. f4018magf - Safford '80 survey (4018) gridded at 200 m.
  17. f4024magf - Needles survey (4024) gridded at 200 m.
  18. f4052magf - Winchester Mountains survey (4052) gridded at 200 m.
  19. f4053magf - Rattlesnake survey (4053) gridded at 200 m.
  20. f4109amagf - San Francisco Peaks survey (4109A) gridded at 200 m.
  21. f4109cmagf - San Francisco Peaks survey (4109C) gridded at 200 m.
  22. f4113magf - San Carlos survey (4113) gridded at 200 m.
  23. f4145magf - Woolsey Peak survey (4145) gridded at 200 m.

GRID PROJECTION SPECIFICATIONS

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Maintained by: Gene Ellis

Last Modified Monday, 15-May-2000 

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For more information about this report contact: Ron Sweeney