Irregularities of the Polar Motion

Abstract

The independent series of coordinates of the pole obtained by the Defense Mapping Agency by observations of Transit satellites (DOP) and by the BIH using classical astrometry only (AST) are considered. They mainly differ by a periodic annual term. After removal of the mean annual difference from AST, the two series are compared. They show common and remarkable irregularities. A derivation of the excitation functions from DOP and AST shows also a good correlation. In the course of this study the constant improvement of DOP, which is now much better than AST, was noticed. The author expresses the opinion that the annual difference between DOP and AST is due to AST, which should therefore be calibrated against DOP.