The North Dakota aeromagnetic grid is constructed from grids that
combine information collected in 13 separate aeromagnetic surveys
conducted between 1978 and 2001. The data from these surveys are
of varying quality. The design and specifications (terrain
clearance, sampling rates, line spacing, and reduction
procedures) varied from survey to survey depending on the purpose
of the project and the technology of that time. Every attempt was
made to acquire the data in digital form. Most of the available
digital data were obtained from aeromagnetic surveys flown by the
U.S. Geological Survey (USGS), flown on contract with the USGS,
or were obtained from other federal agencies and state universities.
Some of the 1980 data are available only on hand-contoured maps
and had to be digitized. These maps were digitized along
flight-line/contour-line intersections, which is considered to be
the most accurate method of recovering the original data. Digitized
data are available as USGS Open File Report 99-557. All surveys
have been continued to 304.8 meters (1000 feet) above ground and
then blended or merged together.
