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  1. Data Management
  2. DM-23545

Analyse differences in photometry between calexp[+externalPhotoCal][+skyCorrection]

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    • Story
    • Status: Done
    • Resolution: Done
    • None
    • None
    • None
    • 16
    • DRP S20-3 (Feb)
    • Data Release Production
    • No

    Description

      When SFM is run, we produce and persist a "calibrated" exposure (calexp) upon which we perform measurements to compute the src catalogs. Subsequently, an "external" calibration can be run (i.e. jointcal/fgcmcal) to compute a more refined set of photometric and astrometric calibrations. Finally, a global sky correction can be performed and applied. The latter two steps are not reflected in the persisted visit-level src catalogs, yet these are the catalogs on which many "visit-level" metrics are computed and tracked. Indeed, the external photo/astrom calibrations can be applied at the catalog level, so their effects can be measured and tracked. However, there is currently no check on the photometry post global sky-correction and just pre-warping into what actually gets included in a coadd. It would be good to know if/what differences there are at these different stages, particularly in assessing the chaining of the measurement and application of these calibrations. In particular, the global sky correction is measured independently of any external photometric calibration and applied subsequently. Does this have any (negative) effects on the effective calibration of the image going onto the warp & coaddition stage?

      Current plan is to make use of the new functionality added on DM-23352 which allows for forced CCD photometry to apply any combination of the above mentioned calibrations (as config options).  Forced catalogs will be created for the different permutations and combinations and the the resulting source catalogs will be compared.

      Note to self: If any "issues" are uncovered, it may be worth a subsequent ticket to look into adding the ability to perform the global sky subtraction (pipe_drivers' skyCorrection.py) on images that have had the external photometric calibration applied.

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            lauren Lauren MacArthur
            lauren Lauren MacArthur
            Eli Rykoff
            Eli Rykoff, Lauren MacArthur, Yusra AlSayyad
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