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Image health seeing and obstac » History » Version 4

James Annis, 12/01/2012 11:53 AM

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h1. Image Health seeing and Obstac
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The lore is that the image health seeing values are sometimes unrelated to the real seeing.
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What do we know?
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DIMM free air seeing values are in red, Quick Reduce produced Sextractor FWHM measures of the
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delivered image quality (free air seeing + dome seeing + optics + tracking) is in green,
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and the Image Health FWHM measures are in blue.
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!{width:1000px}FWHM_IH_QR_DIMM-20121025-20121026.jpg!
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(This image is from Douglas Tucker, October 26, 2012 )
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Note that IH and QR track each other well at small seeing values, but that IH
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has a cutoff at about 1.5".
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If one finds a image with bad seeing, say 2", reported by QR and asks the SISPI
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database for the harmonic_mean_seeing values for all 62 ccds, often there will
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be only a single ccd reported in the database.
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It is likely that Image Health has a threshold above which its seeing measurements
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are thrown away: not used in the fp_harm_mean_seeing calculation and not
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sent to the SISPI database.
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Next, Jiangang (amongst others) points out there is a scale difference between
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IH and QR. Jiangang's report is here
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[[2_Comparison_of_fwhmwhisker_from_different_methods_based_on_images_from_11242012]]
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but I want to point out the following plot:
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!fwhm_QR_IH.png!