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- Cross-talk: Double-check that cross-talk has actually been removed. See if there is still a signature of bright stars in one chip in other chips.
- Bias correction:
- Mask bad pixels:
- Check saturation and bleed problems:
- Check the noise in background of the image. Is it similar to expectations
- Issues from flat fielding / illumination corrections
- Issues from fringe corrections: Check if there are any fringe patterns left in the image, maybe use fourier transform.
- Check the background level across the field. If gain corrections are applied then the background level should be pretty smooth once ISR is finished.
- If there's a sky/background subtraction stage (i.e. setting the background close to zero), then check that this hasn't created artifacts
- Check for leftover cosmic rays that got through the "repair" step.
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- Check that the aperture corrections have the right sign, and see how they vary across the field. Should be pretty uniform.
Coadd
- Check the S/N in the background and the stars, is it what you expect
- Check that regions around bright/saturated stars are okay
Multi-fit / Forced Photometry
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- Check depth of the photometry, is it as deep as expected
- Check resulting chi/sharp or equivalent PSF/shape metrics. Are the median/sigma values as expected? How do they vary with magnitude?
- Check aperture corrections
- Check calibrated photometry against our master/reference LSST catalog
- Is it as expected?
- Any color, airmass or magnitude trends?
- Is the scatter wrt the reference catalog as expected and similar to the photometry noise?
- Are we getting the S/N that we should be getting according to the model?
- At the catalog level we can:
- Compare stack-reduced image to a reference catalog (e.g. SDSS Stripe82)
- Compare reductions of images with the stack and other software packages (e.g. DAOPHOT, DoPHOT, SExtractor, etc.)
- Compare stack reductions of simulated images to truth tables.
Photometric Calibration
- Check the calibration by measuring the scatter in the stellar locus across a field. Compare this to the stellar locus scatter in the instrumental photometry. This isn't an absolute calibration check, but it's a check that the calibration terms are actually improving the relative calibration over a larger field.
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