| | 1 | == February 9, 2012 Results == |
| | 2 | |
| | 3 | === Continuity === |
| | 4 | |
| | 5 | After some development work and debugging, a new PATTERN.CONTINUITY correction has been implemented that is applied to all OTAs and supersedes the previous PATTERN.CELL correction. As proposed below, the median value along each edge of each cell is calculated, and a set of cell-by-cell offsets is calculated from the differences between the edges of adjacent cells. These offsets are applied, with the assumption that by minimizing the cell-to-cell offsets, we will supply the background fitting code with a smooth and continuous function to fit. Applying this correction to the example case used previously: |
| | 6 | |
| | 7 | [[Image(bkg_continuity.png,800px)]] |
| | 8 | |
| | 9 | [[Image(bkg_continuity_profiles.png,800px)]] |
| | 10 | |
| | 11 | After testing that this method works as intended, a new processing of the SAS g-filter footprint data was run using this correction (label czw.footprint_continuity2.bkg, data_group czw.20120209.footprint.g). Shown below is a comparison between the original IPP processing, the updated PATTERN.ROW "czw" reduction, and the newest continuity applied reduction. To make this easier, I've chosen the skycell used in Nigel's discussion on the DRAVG page (skycell 1405.030). |
| | 12 | |
| | 13 | [[Image(oldipp_skycell.1405.030.png,800px)]] |
| | 14 | [[Image(patternrowfix_skycell.1405.030.png,800px)]] |
| | 15 | [[Image(continuityfix_skycell.1405.030.png,800px)]] |
| | 16 | |
| | 17 | The continuity correction does seem to resolve the cell-level banding that is visible in the previous reductions. The entire set of stacks will be available on the distribution server by the end of today. |
| | 18 | |
| | 19 | === Ripples === |
| | 20 | |
| | 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. |
| | 22 | |
| | 23 | [[Image(o5744g0329o.png,800px)]] |
| | 24 | |
| | 25 | [[Image(convolved_stack.png,800px)]] |
| | 26 | [[Image(unconvolved_stack.png,800px)]] |
| | 27 | |
| | 28 | We currently do not understand the source of these ripples, nor do we have a solution at the moment. |
