Details
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Type:
Story
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Status: Done
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Resolution: Done
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Fix Version/s: None
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Component/s: meas_algorithms
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Labels:
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Team:External
Description
Ikeda-san has reported that the background tweak being applied in the DynamicDetectionTask is excessive when there are bright stars in the field.
On investigation, found that sky objects are correctly avoiding the DETECTED areas, but the DETECTED area isn't anywhere as large as it seems just by looking at the image because the extended emission from the star is being purposely suppressed by the code (so the deblender isn't overwhelmed; this is the "wide temporary background" feature).
Suitable results can be obtained by doing an explicit background subtraction (using the base_LocalBackground measurement algorithm).
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I included some stupid questions on the PR because I had trouble following why you could reuse some variables from above, but not others. Maybe add a comment about why you're reconvolving but using the previous middle/sigmas.
Yusra AlSayyad, your questions weren't stupid but very helpful. I've made some changes and spent some time crafting a suitable test (with thanks to John Parejko for the prompting). Would you mind having another look?
Paul Price
added a comment - Yusra AlSayyad , your questions weren't stupid but very helpful. I've made some changes and spent some time crafting a suitable test (with thanks to John Parejko for the prompting). Would you mind having another look? It's still not obvious to me why that sigma is the right one to pass to finalizeFootprints. The test makes sense, but just to double check we don't normally use config.thresholdType = "pixel_stdev" for detections on coadds, right?
We do use pixel_stdev for detection on coadds.
The alternative to that sigma is the one passed to the method, which may be None. The sigma I'm using will be the one passed to the method if it's non-None, or the appropriate value for the provided PSF: see here.
Paul Price
added a comment - We do use pixel_stdev for detection on coadds .
The alternative to that sigma is the one passed to the method , which may be None . The sigma I'm using will be the one passed to the method if it's non- None , or the appropriate value for the provided PSF: see here . Thanks for the clarification. OK to merge when it passes Jenkins
Jenkins is green.
Paul Price
added a comment - Jenkins is green. Merged to master.
Paul Price
added a comment - Merged to master. 
Thanks for volunteering to review this, Yusra AlSayyad.
pprice@tigressdata:/scratch/pprice/meas_algorithms[tickets/DM-14119] $ git subcommit 6816c1e76c710c74b3e4008e071587b495657a6aAuthor: Paul Price <price@astro.princeton.edu>Date: Mon Apr 16 19:40:00 2018 -0400dynamicDetection: make robust against extended emissionby applying an explicit background subtraction using thebase_LocalBackground measurement algorithm. Otherwise, extendedlow-level background (e.g. around bright stars) can contaminateour measurements.python/lsst/meas/algorithms/dynamicDetection.py | 12 ++++++++----1 file changed, 8 insertions(+), 4 deletions(-)