Spherical Harmonic Analysis in the Presence of High Harmonics

Abstract

Spherical harmonic analysis of the geomagnetic field is usually done by using the method of least squares in conjunction with a truncated spherical harmonic series. The results obtained are very dependent on the weighting used, the distribution of the observational data and the degree of truncation, especially for shallow sources that give rise to high harmonics. This research note discusses the inter-play between weighting and truncation by using simple sources for which the precise coefficients are known.