Accuracy and Precision of GPS Carrier-Phase Clock Estimates
Abstract
The accuracy of GPS-based clock estimates is determined by the pseudorange data. For 24-hour arcs of global data sampled at 5-minute intervals, the formal errors for the clock estimates are typically about 115 ps. An internal test of the actual time transfer measurement accuracy has been made by comparing clock estimates at the boundaries between successive analysis arcs for receivers equipped with very stable oscillators, using the combined daily clock estimates provided by the International GPS Service (IGS). During the period 29 October 2000 to 28 July 2001, the observed day-boundary discontinuities or individual IGS stations have distributions well described as zero-mean and Gaussian. However, the variances among the 23 stations span a wide range, from rms values of about 170 ps to 1200 ps, implying time transfer accuracies ranging from about equal to the formal errors to nearly an order of magnitude greater. For a few stations, the performance changes dramatically with time. Since the same receiver and antenna models are common for many stations, it is likely that the dominant site-dependent effects are related more to local factors affecting data quality than to specific hardware choices. The ALGO and NRC1 station display notable temporal variations that might be seasonal. We find that a portion of the variability is caused by sensitivities to long-term temperature changes, with coefficients of -101 ps/deg C and 156 ps/deg C. Smaller, less significant temperature-dependent effects are seen at some of the other stations. The precision of clock estimates within a given analysis arc is usually assumed to be better than indicated by the formal errors or the accuracy measures because the relative clock estimates are determined mostly by the carrier-phase observations.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 2001
- Accession Number
- ADA485022
Entities
People
- J. Ray
- K. Senior
Organizations
- United States Naval Observatory