The program calculates the Earth's magnetic field components at a given point in space and time from a spherical harmonic expansion of the main (core) field. The program accepts geodetic or geocentric coordinates and accommodates Gauss-normalized as well as Schmidt-normalized coefficients. In a first step the coefficients are determined for the time in decimal years required by the user. In its present form the package includes the coefficients of the IGRF (10/68) model, which is of degree and order 8 in its constant and first derivative term (epoch 1965, oblateness considered). But other sets of spherical harmonics coefficients can be easily adopted for use with FIELDG.
Availability: On one tape (NSSDC ID #PG-11A)
J. C. Cain, S. Hendricks, W. E. Daniels, and D. C. Jensen, Computation of the Main Geomagnetic Field from Spherical Harmonic Expansions, National Space Science Data Center, Report 68-11, Greenbelt, Maryland, 1968. (Revised version of NASA-TM-X-611-64-316, 1964) (B01411)
NASA Official: Dr. Robert McGuire, Head of the Space Physics Data Facility