XRT CCD contaminantion uncorrected spots: location and growth.
(10 Apr 2017 by Aki Takeda)
0. Motivation.
In recent synoptic composite images, at least 4 relatively big
contamination spots are noticable
(an example) at the region between 0 and 20N degree latitude in the
Eastern hemisphere.
These spots are supposed to be cosmetically corrected by spot-correcting
code, XRT_SPOTCOR, which is now included in XRT_PREP. The appearance of
these uncorrected spots indicates that either (1) these spots are newly
built up and thus not processed by the current code based on the old
spot map, or (2) for some reason the current code started to fail to
correct them.
1. Situation before August, 2016.
A big contamination spot became noticeable since January, 2015 at the
North of CCD center (see center image below), in the synoptic composite
images (i.e., images after PREP).
This indicates the contamination spot correction program
(XRT_SPOTCOR.PRO) started to fail to correct this spot.
Since May 2016, this spot is corrected by XRT_ERASER.PRO,
which is prepared to correct only this spot. The right image below
is a successful example of XRT_ERASER applied to an
Open/Al-mesh image taken on 5-Apr-2016.
- Case of 2016/04/05 (Click image to enlarge).
| Before PREP |
After PREP
(circle shows location of spot) |
PREP + XRT_ERASER |
|
|
|
2. Situation after August, 2016.
Since August, 2016, 4 new relatively big spots started to appear
uncorrected by XRT_SPOTCOR. Location of these spots are
shown by circles in the second image ("After PREP") below. The center
coordinates of the circle (hopefully close enough to those of spot
center) measured in this 1024x1024 image are (from East to West):
- [133,650]
- [234,595]
- [308,560]
- [482,560]
- Case of 2017/03/21 (Click image to enlarge).
| Before PREP |
After PREP
(circles show location of spots) |
PREP + XRT_ERASER |
PREP + XRT_ERASER*2
(XRT_ERASER applied twice) |
|
|
|
|
3. Growing history
Movie of level0 data (before PREP) obtained for the synoptic programs.
(click image to see a java-script movie).
- Open/Al-mesh, long-exposure images,
- Cut out NE region with the size 900x600 pixels.
- From 2013/02 to 2017/03 with irregular sample period.
All uncorrected big spots (4 spots introduced in sec.2 as well as
the big North spot introduced in sec.1) are NOT newly-born spots.
They did exist at least as of 2013/02, but with smaller size.
It seems that those spots grew so big that the current program
(map of spot location) started to fail due to a mismatch between
true and assumed size.
4. Quick-fix solution
On 11-Apr-2017, Trish Jibben (SAO) modifed the XRT_ERASER.PRO so that
it handles additional 4 big spots to the original big one in North.
Below images demonstrate the performance of the new XRT_ERASER.
Both image NOT processed with XRT_PREP before applying XRT_ERASER.
Solar image from 1-Apr-2017 17:03:37, by courtesy of T. Jibben.
Click image to enlarge.
| Before new XRT_ERASER |
After new XRT_ERASER |
|
|
Performance check on synoptic images. Click image to enlarge.
| with old XRT_ERASER |
with new XRT_ERASER |
|
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