Combining GAIA windows I: SNR calculations of secondary sources in the ideal

During 5 year observational phase of GAIA, several one-dimensional observations are obtained from the same objects at di®erent epochs and transit angles. It is scienti¯cally important to combine all the observations to produce a two-dimensional image that contains all the data. This al-lows us to ¯nd much fainter stars surrounding the main source than what would be possible to ¯nd in single observations on-board the satellite or in individual transmitted patches. Most of the emerging objects are phys-ical secondary stars, but also some background/foreground objects can be found. The combination procedure also increases the image resolution in the cross-scan direction. The procedure consists of combining patches that are stretched back to 2-D images when the original centroid positions of windows are known. Transit angles, i.e. image rotations, can have values between 0 ± and 360±, which are generally not uniformly distributed. The initial image window from which patches are taken is not a square, but i