On the identification of Magsat anomaly charts as crustal part of the internal field

Satellite magnetic anomaly charts are derived from the measurements by subtracting a global field model regarded as representative of the core field, after removal of the external field effects. The field model comprises all spherical harmonic terms of the internal field up to a certain degree n, say n = 13. Hence the large‐scale constituents of the crustal field are also removed from the anomaly charts. The calculated magnetic field of a global magnetization model of the earth's crust gives an estimate of the lacking lower‐order crustal terms. It turns out that the omitted crustal field part is of the same order of magnitude as the rest of the field. The geographic distribution of the omitted model field part on a continental scale is closely correlated with the depth of the Moho. By analogy, the same conclusion is drawn with respect to the actual crustal field. This result accounts for the fact that in the satellite charts the continental margins are not very well reflected. Considerable corrections are therefore required if the anomaly charts are intended to display the whole crustal field.