This data set contains the 296 coefficients of the IGS (75) spherical harmonics model of the Earth's main (core) magnetic field. The coefficients are for epoch 1975.0 and extend to degree and order 12 in the constant terms, 8 in the first derivative terms, and 6 in the second derivative terms. The model is based on data from ground stations, aircraft flights, ocean surveys, and the OGO satellites (see also POGO (8/71)).
D. R. Barraclough, A Model of the Geomagnetic Field of Epoch 1975, Geophys. J. Royal Astr. Soc. 43, 645, 1975.