Time-delay Integration Ccd Readout Technique: Image Deformation

SUMMARY The introduction of electro-optical tracking with CCDs has revitalised the research potential of the transit telescope. Termed the Time-Delay Integration (TDI) readout technique (or drift scanning), this method ooers exceedingly good at-elding performance. While this asset is not disputed, there has been no quantitative analysis of potential drawbacks of the TDI technique. The work presented here is the rst study of the two main sources of image deformation intrinsic to TDI data: (1) the discrete shifting of CCD pixels to match a continuously moving object leads to a symmetrical elongation of the object's east-west proole, and (2) the curvature of objects across the CCD columns results in an asymmetrical image deformation and shift of the peak intensity in the north-south direction. It is found that undersampled data (i.e., Gaussian point-spread-function standard deviations < 0:85 pixels) suuers severely due to the rst source, while star trail curvature deviations > 0:8 pixels can lead to images susceptible to the second. A comparison between three systems which utilise the TDI mode is also presented.