METHODS OF COMPUTATION OF GEOMAGNETIC FIELD AT GREATER ALTITUDE IN A LOCAL REGION

In this paper two methods have been given to calculate the geomagnetic fields at great altitudes in a local region.In the first method surface spline is used to express the distribution of the geomagnetic fields and its horizontal gradient on the ground surface, the formulas areThe surface spline can express both normal distribution and anomalous distribution of the geomagnetic fields, and also geomagnetic horizontal gradient, so the use of surface spline makes Zmuda’s method simpler.The other method is with the aid of spherical harmonic analysis of the geomagnetic fields in a local region, the procedure is(1)to compute a set of spherical harmonic coefficients based on the geomagnetic data on the ground surface in a local region, (2)to compute the geomagnetic fields at great altitudes by using these coefficients.