A Comparison of CEI, VLBI, BIH and USNO Earth Orientation Information

Résumé du livre

Two radio astrometric techniques used to determine the earth's orientation in space are examined. Comparisons are made of the earth orientation information obtained by the connected-element interferometry (CEI) method and the very long baseline interferometry (VLBI) methods against the standard data sets of the U.S. Naval Observatory (USNO) and the Bureau International de l'Heure, and the two sets themselves are intercompared. The analysis shows that in the polar coordinates the USNO and BIH have nearly the same accuracy. The VLBI data, from the National Geodetic Survey's Project Polaris, show degraded accuracy in x, and there are too few independent determinations in y by Polaris to analyze them properly. Good agreement is seen between the USNO and Polaris residuals in UT1-UTC, indicating that the BIH is too heavily smoothed and fails to account for rapid changes (on the order of a few weeks) in the earth's rate of rotation. The major contributor to the USNO UT1-UTC is the connected element interferometer. It is imperative that the present sources continue to be available to USNO for input to the system, and highly desirable that additional high-precision, reliable sources be added.