U.S. Naval Observatory Earth Orientation Department

The Global Positioning System (GPS) Analysis Program produces high-quality estimates of polar motion and UT1-like variations, GPS satellite orbits, clocks for the tracking station and satellites, and other quantities from observations of the GPS satellites. This work is done in close conjunction with the International GPS Service and relies upon the IGS global tracking network. The IGS polar motion results dominate in the IERS Bulletin A combination due to their high accuracy, reliability, and rapid availability. The GPS-based UT1-like results, while lacking a direct or absolute link to the celestial reference frame, are very useful for interpolating UT1 information when none is available from VLBI and for extrapolating to the most recent times after the latest VLBI observing session.

Together with seven other Analysis Centers, the Earth Orientation Dept. serves as an IGS Associate Analysis Center for Rapid Service and Predictions. As such, orbit, clock, and EOP information is submitted daily to the IGS Analysis Center Coordinator for combination into the IGS Rapid products, which are delivered each day by ~17:00 UTC using data from the previous day. In addition, predicted GPS orbits are submitted for incorporation into the IGS combined Predicted products. To obtain these results, please refer to the IGS Data and Products web site. A summary of our current analysis procedures is available in this file.

In addition, the Earth Orientation Dept. participates in the IGS/BIPM Pilot Project to Study Accurate Time and Frequency Comparisons Using GPS Phase and Code Measurements. This project aims to develop methods to use GPS phase and code measurements for improved worldwide availability of accurate time and frequency. In support of this project, USNO clock results are distributed to researchers via our web site.

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Last modified: 24 July 2009 Approved by EO Dept. Head, USNO