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Session 9 - Instruments, Techniques.
Display session, Monday, June 09
South Main Hall,

[9.05] A Comparison of Radio and Optical Astrometric Reduction Algorithms

G. H. Kaplan (USNO)

This paper examines the correspondence between two approaches to astrometric observational reductions: the approach based on angular observables used for optical observations, and the approach based on the interferometric delay observable used for VLBI observations. Specifically, of interest here are the algorithms that account for annual and diurnal aberration and gravitational light-bending. These algortihms are important because they must be applied to all wide-angle astrometric measurements, whether ground- or space-based, and regardless of the distance of the objects observed.

A procedure is presented by which VLBI algorithms can be used for optical observations. This scheme can help to guarantee consistent treatment of observational results in the two regimes. It also allows for the evaluation of the precision of the algorithms. Differences between angle-based and delay-based algorithms in current use are shown to be less than 1 microarcsecond. However, the physical models used must be improved to reach external accuracies at such levels.

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