The geomagnetic field: 1970-1990 and the NASA candidate models for DGRF 1985 and IGRF 1990

Abstract

All available magnetic data from observatories, satellites, repeat station measurements, and aeromagnetic, shipborne and land surveys are used to derive spherical harmonic models of the geomagnetic field from 1970 to 1990. Two models are derived, designated GSFC(11/90)D and GSFC(11/90) respectively. Main field coefficients are determined up to degree 13 and temporal variation, represented by B-splines, up to degree 10. Bias values at the fixed observatories were included as part of the solution. The secular variation models are smoothed by use of norm minimization. The resulting secular variation shows a jerk-like trend change in several coefficients near 1979. -from Authors