| 21 | 21 | Although the cell-scale issues seem to be resolved by this correction, a lower level camera feature can be clearly seen in these new stacks. We use the PATTERN.ROW correction to remove row-by-row bias offsets that are present on the detectors (in the warps and stacks, rows run vertically on these images). We apply this correction sparingly, as it creates the "butterfly" patterns around bright stars, so it is limited to only the cells that have the worst row-by-row offsets. Previously, our assumption was that these offsets were random, and so any variations on cells without the PATTERN.ROW correction would be eliminated in the stacks. However, the new stacks show that there are larger correlations between these offsets that are reinforced by the stacking, showing up as wide (~5 pixel) ripples in the background. Looking at the input warps for this stack skycell shows that there does not seem to be a time trend in the amplitude of the ripples (such that sequential exposures have similar structure), but it does seem that the peaks and troughs are more likely to fall in the same location than not. Because of this amplification, as the number of input warps increases, the signal to noise of these ripples increases, making peaks likely sources of false detections. |
