Correlations between GPS and USNO Master Clock time

Abstract

The U.S. Naval Observatory Master Clock is used to steer the Global Positioning System (GPS) time. Time transfer data consisting of the difference between the Master Clock and GPS time has been acquired from all satellites in the GPS constellation covering a time period from 10 October 1995 to 12 December 1995. A Fourier analysis of the data shows a distinct peak in the Fourier spectrum corresponding to approximately a one day period. In order to determine this period more accurately, correlations are computed between successive days of the data, and an average of twenty five correlation functions shows that there exists a correlation equal to 0.52 at delay time 23 h 56 min, which corresponds to twice the average GPS satellite period. This correlation indicates that GPS time, as measured by the U.S. Naval Observatory, is periodic with respect to the Master Clock, with a period of 23 h and 56 min. An autocorrelation of a five day segment of data indicates that these correlations persist for four successive days.