Polar motion determined by Doppler satellite observations

Doppler observations of Navy Navigation Satellites have been used to comput pole positions on a daily basis since 1969. Limited computations have been performed using data on file for the period 1964–1969. Results of recent computations give a standard error in pole position based on 48 hours of Doppler observations of 7 cm. However, effects of errors in the orbit due to uncertainties in the gravity field prevent the attainment of this precision; the standard deviation of pole position for this time span is 60 cm, giving a standard error for a five day mean based on observations of two satellites of 25 cm.