1985 magnetic models for the United States



The U.S. Geological Survey (USGS) has developed new mathematical models of the magnetic field in the United States. The models describe the direction and intensity of the field at the beginning of 1985 and the rate of change expected during the next few years. They were derived from several tens of thousands of original field measurements from land, marine, and aerial surveys; from values synthesized from the Magsat-based International Geomagnetic Reference Field (IGRF) model for 1985; and from recent data from magnetic observations and repeat stations. The models will serve as the basis for a new set of magnetic charts, now in preparation. Figure 1 is a simplified small-scale version of the chart of declination.