World magnetic chart model for 1980

The 1980 World Magnetic Chart model is the product of a joint effort by the United States and the United Kingdom. It will be used to construct the 1980 World Magnetic Declination Charts published by the Defense Mapping Agency Hydrographic/Topographic Center in the U.S. and the British Hydrographic Department in the U.K. As is customary the model consists of Schmidt quasinormalized coefficients of the spherical harmonic expansion of the internal geomagnetic field. The main field coefficients are of degree and order 12, and the secular field coefficients are of degree and order 8.