DESCRIPTIONS OF THE GEOMAGNETIC FIELD

This report is concerned with the geomagnetic field from a control specialist's point of view. It contains a brief historical background of the subject and an explanation of the field's significance to control engineers. The gross features of the field are described as determined from surface and satellite measurements, and as currently understood by geophysicists. Spherical harmonic expansion, simple dipole, titled dipole, translated dipole, and quadrupole field models are presented. An error analysis showing the magnitude and directional differences between each of the four approximate models and the more exact Hendricks and Cain spherical harmonic expansion model for 1967.0 is included for evaluation of model adequacy and accuracy. Notable field abnormalities are discussed. (Author)