This data set contains the 248 coefficients of the AWC (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 and to 8 in the first derivative terms. The U.S. Geological Survey (USGS) publishes an update of the main field and its secular variation every five years. This edition is based on approximately 100,000 surface, marine, and aeromagnetic measurements from 1939 through 1974 (see also POGO (8/71)).
Availability: On one tape, networks (NSSDC #MG-1AA)
N. W. Peddie and E. B. Fabiano, A Model of the Geomagnetic Field for 1975 (AWC/75), J. Geophys. Res. 81, 2539, 1976.
NASA Official: Dr. Robert McGuire, Head of the Space Physics Data Facility