|U.S. Naval Observatory||Earth Orientation Department|
The Reference Frame Program observes galactic and extragalactic radio sources at remote sites using the technique of Very Long Baseline Interferometry (VLBI) to produce and maintain a catalog of radio source positions accurate at the milliarcsecond level.
VLBI observations scheduled and analyzed by the Earth Orientation Department and other member organizations of the National Earth Orientation Service (NEOS) form the basis of the International Celestial Reference Frame (ICRF) adopted by the International Astronomical Union (IAU) as the fundamental celestial frame. These VLBI data have also been the major component of all past realizations of the International Earth Rotation and Reference Systems Service (IERS) Celestial Reference Frames. Earth Orientation Department personnel were among the authors of the Radio Optical Reference Frame (RORF), produced by the complete re-analysis of all compatible VLBI data available through the end of 1993, and were among the members of the IAU Working Group on Reference Frames which produced the ICRF for the IAU.
Through participation in the NEOS, Earth Orientation Department personnel are actively involved in the maintenance of the ICRF. New observations specifically designed to monitor ICRF sources are continuously scheduled and analyzed. ICRF sources are also imaged at radio wavelengths to monitor their intrinsic structure. A Radio Reference Frame Image Database (RRFID) is maintained to disseminate the results of the imaging observations.