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Chapter 12
FGS Error Sources
In This Chapter...
Levels of POSITION Mode Errors / 12-1
Observation-Level POSITION Errors / 12-2
Visit-Level POSITION Errors / 12-11
Field-Level POSITION Errors / 12-13
TRANSFER Mode Errors / 12-14
The previous chapters have described TRANSFER mode and POSITION mode observations. Some FGS error sources are mode-specific, while others are common to both modes. This chapter discusses those uncertainties, both statistical and systematic, which remain after the pipeline calibrations of raw POSITION mode and TRANSFER mode observations. Each step in the calibration procedure leaves its own residuals which contribute to the overall error budget.
The increasingly common use of the FGS astrometer for mixed-mode observations, in which TRANSFER mode and POSITION mode observations are made in the same visit, combines the errors associated with each mode and introduces new sources as well. The next chapter discusses the analysis of mixed-mode observations and the associated errors.
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