U.S. Naval Observatory Earth Orientation Department

The Very Long Baseline Interferometry (VLBI) Analysis Program observes galactic and extragalactic radio sources at remote sites using the technique of VLBI for the determination of astro-geodetic information.

VLBI data are the most accurate data available to estimate polar motion, UT1, precession and nutation. All other data types used for Earth Orientation Parameters (EOP) determination (eg. Global Positioning System, laser ranging, etc.) are "calibrated" with respect to the VLBI determinations. The VLBI data are also used to determine and maintain the positions of the extragalactic radio sources which form the basis for the celestial reference frame within which the EOP parameters are determined.

The VLBI data are correlated and analyzed at the Washington Correlator (WACO), which is operated and maintained by the Earth Orientation Department, in close cooperation with the VLBI Group of the National Aeronautics and Space Administration's Space Geodesy Program. The WACO is located in Washington, D.C. on the grounds of the U.S. Naval Observatory.

Department personnel also undertake geophysical studies such as the secular motion of the pole, continental drift, Earth tides and corrections to the fundamental astronomical constants in order to improve the determination and prediction of Earth orientation parameters.

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