This data set contains the 147 coefficients of the GSFC (9/65) spherical harmonics model of the Earth's main (core) magnetic field. The coefficients are for epoch 1960.0 and are based on about 197,000 survey data gathered between 1945 and 1964. The coefficients extend up to degree and order 9 in the constant term and to degree and order 6 in the first time derivative. The oblateness of the Earth (flattening factor of 1/298.3) has been considered in the determination of the coefficients. Geomagnetic field parameters can be generated with the ALLMAG (#PG-12A) program.
S. J. Hendricks and J. C. Cain, Magnetic Field Data for Trapped-Particle Evaluation, J. Geophys. Res. 71, 346, 1966.