The USGS pioneered the first airborne magnetic survey in 1945. Subsequently, the USGS has acquired aeromagnetic data for essentially all of the U.S. in a piecemeal fashion. Surveys were designed for many purposes, thus they varied widely in both size of coverage and anomaly resolution, determined primarily from flight height and line spacing. Data collection spanned changes in acquisition techniques, from analog-based before the 1970's to current digital systems utilizing Global Positioning System (GPS) navigation. After more than 50 years, the USGS' digital and analog archives of aeromagnetic data comprise more than 1,000 surveys consisting of nearly 8,000,000 line-km of data that would cost hundreds of millions of dollars to re-fly today.

For the national compilation that forms part of the North American database, the USGS has constructed a database containing the original aeromagnetic survey data, in digital form, from surveys and maps of existing public-domain, and where available, proprietary magnetic data (about 5,800,000 line-km). These data either exist as digitally processed flight-line data or were derived from analog maps if the flight-line data were not available. The ASCII data sets for publicly-available aeromagnetic surveys of the U.S. are available on-line or on disk. In this poster, we document the history of aeromagnetic data collection in the U. S. and describe both the construction of the ASCII database and the metadata files that provide information about each survey.