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Check platescale over mission using measured occulter diameter #363
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The effective focal length of K-Cor Objective lens, using data from JenOptiks and Corning, is 2018.5 +/- 0.2 mm. K-Cor occulter diameters in mm (+/- 0.00254 nm - estimate from Dennis email):
Using the focal length and occulter sizes (ala UCoMP): magnification = distortion-corrected occulter_radius_in_pixels / (occulter_diameter_in_mm / 2.0)
platescale = 206264.8 / magnification / focal_length |
I have notes about a OC-1018.9" occulter. Was this never used? |
Mike: Thank you for pointing that out. We swapped out the 'old' winter occulter of 1018.9" on Jan 12, 2021 for the new tapered winter occulter. I had forgotten about that. I edited my info above to include both the old and new occulters. Thanks! |
I am running code that calculates level2$ for f in *_kcor_l2.fts; do echo $f; fitscat -r $f | grep IMAGESCL; done
20221007_171731_kcor_l2.fts
IMAGESCL= 5.6105 / [arcsec/pixel] image scale for this file
20221007_171746_kcor_l2.fts
IMAGESCL= 5.6100 / [arcsec/pixel] image scale for this file
20221007_171801_kcor_l2.fts
IMAGESCL= 5.6098 / [arcsec/pixel] image scale for this file
20221007_171816_kcor_l2.fts |
Not surprising. I have been spot-checking days and getting platescles as much as 0.06 arcsec/pix different - always less than the 5.643 arcsec/pix I got back in 2013-early 2014. Using the larger difference of 0.06 arcsec/pixel as a worse case, we are off by 0.03 solar radii at the outer edge of the field-of-view (the error is much smaller closer to the occulter). That is not awful. The smallest error bar I use for measuring CME positions in the best images is 0.03 solar radii. Many measurements are twice that. Nevertheless, the platescale is off and needs to be recomputed. I will set up a separate ticket for that. Yesterday, I asked Ben to retrieve 2 of the K-Cor occulters next time he is at MLSO. I want him to mail those back and have the IG measure them again. It is also possible that a change in distortion correction is playing a role. So glad you are going to save this info in the headers. |
Thanks very much for doing this. Just to clarify the above plot: the red line is the platescale (5.643). Is the black vertical line near the end of the mission the image scale? Are you plotting the distortion corrected occulter radius for each camera separately? |
The black vertical line is comprised of the image scale values for a single day. These image scale values are computed from the average of the two distortion corrected radii. I could store separate |
The CSV file looks like:
|
Use the occulter radius size from the routine
kcor_find_image.pro
to compute an image platescale. Record the value of the image platescale in the FITS header keywordIMAGESCL
. Image platescales will be compared with the original determination of the instrument platescale derived from the K-Cor effective focal length calculated by Dennis Gallagher, and the lab measurements of the K-Cor occulter diameters.Tasks
IMAGESCL
keywordIMAGESCL
keyword to databaseIMAGESCL
in end-of-dayRCAM_SCL
andTCAM_SCL
FITS keywords ("distortion corrected image scale for camera {0,1}")rcam_image_scale
andtcam_image_scale
kcor_eng
table fieldsIMAGESCL
in end-of-day; use different color or symbol for each cameraIMAGESCL
,RCAM_SCL
,TCAM_SCL
, andRCAM_SCL
-TCAM_SCL
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