AAS 205th Meeting, 9-13 January 2005
Session 91 Surveys and Catalogs
Poster, Wednesday, January 12, 2005, 9:20am-6:30pm, Exhibit Hall

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[91.13] Improving Astrometric VLBI by using Water Vapor Radiometer Calibrations

C. S. Jacobs, S. J. Keihm, G. E. Lanyi, C. J. Naudet, L. Riley, A. B. Tanner (JPL)

Astrometric observations of distant active galactic nuclei (AGN) using the VLBI technique have been used to construct quasi-inertial global reference frames, most notably the International Celestial Reference Frame (ICRF) which now forms the basis for all astrometry including deep space navigation.

The accuracy of VLBI global astrometry has long been limited by systematic errors--most notably stochastic fluctuations of the refractive delay caused by atmospheric water vapor. In order to calibrate the water vapor induced path delay fluctuations, a pair of advanced design water vapor radiometers (AWVR) have been built and deployed. We will present intercontinental VLBI results calibrated with the AWVRs showing a factor of 2.5 to 3 improvement in phase delay residuals over time scales of 10 to 1000 seconds. These results suggest that it may be possible to develop the next generation ICRF (at X/Ka-band) much more rapidly than previously estimated and that spacecraft navigation may be possible at sub-nanoradian levels of accuracy.

The research described in this paper was done at the Jet Propulsion Laboratory, California Institute of Technology under contract with NASA.

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© 2004. The American Astronomical Society.