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3.2.1 Flat-Fielding

The first step in the reduction of galaxy surface photometry, the Flat-Fielding is the correction of errors introduced by differences in sensitivity between different regions of the focal plane. These are essentially due to two effects, namely differences in the intrinsic sensitivity of the detector elements, e.g. the pixels of a CCD, and to dimming of images towards the edge of the field of view. The errors arising from this correction usually dominate the final error budget, e.g. in HST observations, but in the case of GAIA they are expected to be negligible, at least as far as the mission average measurements are concerned. This is because the superposition of measurements obtained from a large number of scans at different positions and position angles will effectively average over any non-uniformities, thus reducing the flat-fielding errors to negligible levels.
next up previous contents
Next: 3.2.2 Sky Background Up: 3.2 Galaxy Surface Photometry Previous: 3.2 Galaxy Surface Photometry   Contents
Mattia Vaccari 2000-12-05