XRT Stray Light Study 7 -- Measurement and Correction.
Link to  the 5th and 6th test page.
(14 August, 2014 by Aki Takeda)
 1. About the 7th tests (performed in the 2014/08/07 timeline).
 Purpose.
-  collects light curves of the XRT eclipses.
-  first attempt to obtain off-point stray-light images 
(Ti-poly & C-poly) at N-pole, S-pole, E-limb and W-limb pointings. 
Pointing coordinates determination:
- N- and S-pole pointings were chosen to be the same as the HOP81 
(Polar Monitoring Campaign). Their pointing coordinates are calculated as:
 (default value) + (offset) .
The default value is (0,900) for the N-pole and (0,-920) 
for the S-pole observations. The offset is the difference
between Hinode and XRT pointings, calculated by Shimizu-san every week 
using the result of the co-alignment programs. That way, the XRT observes 
the area centered at (0,900) and (0,-920) year-round during HOP81.
For the week of 2014/08/08, the offset value was announced as (11,35), 
so the polar pointings were calculated as follows.
N-pole:  (0,900) - (11,35) = (-11, 865)
S-pole: (0,-920) - (11,35) = (-11,-955)
 
- E-limb and W-limb pointings were determined less attentively. 
This time, the values used in the HOP130 (Full Disk Slot Scans) 
was chosen. 
E-limb:  (-936,0)
W-limb:  ( 936,0) -- not performed this time.
 
Exposure time determination:
-  For the polar pointings, the exposure time was chosen to 4096 ms for 
the both Ti-poly and C-poly filters. This value is used in some of the 
HOP81 XOBs for Ti-poly.
 
-  For the E- and W-limb pointings, the exosure time is same as the
current synoptic XOBs (the longest exposure of the Ti-poly triplet,
the longer of the C-poly doublet).
The tests were performed on:
-  8-Aug-2014, 18:56 -- 19:30UT  (at N-pole).
-  8-Aug-2014, 20:40 -- 20:50UT  (at E-limb).
-  8-Aug-2014, 22:15 -- 22:30UT  (at S-pole).
-  no good time window found for the W-limb pointing.
 Solar condition.
 
 
 2. Test sequences.
 N-pole sequence.
-  18:56:00 -- s/c pointing to the North pole (-11,865)
-  19:03:00 -- test sequence started (until ~19:16).
  
  -  -----------------------------------------------------------------------------------------------------------------------------------------------
  
-  1024x1024 pix, 2" resol., Full-Sun, Ti-poly and C-poly long/short 
  exposures.
  
-  256x256 pix, 2" resol., every 10 sec on the center FOV, 
  Ti-poly + G-band(VLS close).
  
-  1024x1024 pix, 2" resol., every 60 sec, Full-Sun, Ti-poly and C-poly.
  
-   detailed parameters of the sequence (XOB#1A30). 
  
-  -----------------------------------------------------------------------------------------------------------------------------------------------
     
 
-  19:06:00 ------   XRT entering twilight zone.
-  19:15:00 ------   XRT s/c night entry.
-  19:16:00 ------   pointing changed to AR12132.
-  19:22:00 ------   XRT s/c night exit.
-  19:25:00 ------   XRT SAA entry.
-  19:31:00 ------   XRT exiting from twilight.
 E-limb sequence.
-  20:40:00 -- s/c pointing to the East limb (-936,0).
-  20:41:00 -- test sequence started (until ~20:54). <--- pointing not 
stabilized yet.
  
  -  -----------------------------------------------------------------------------------------------------------------------------------------------
  
-  1024x1024 pix, 2" resol., Full-Sun, Ti-poly and C-poly long/short 
  exposures.
  
-  256x256 pix, 2" resol., every 10 sec on the center FOV, 
  Ti-poly + G-band(VLS close).
  
-  1024x1024 pix, 2" resol., every 60 sec, Full-Sun, Ti-poly and C-poly.
  
-   detailed parameters of the sequence (XOB#1A2F). 
  
-  -----------------------------------------------------------------------------------------------------------------------------------------------
  
 
-  20:44:00 ------   XRT entering twilight zone.
-  20:53:30 ------   XRT s/c night entry.
-  20:54:00 ------   pointing changed to AR12132.
-  21:00:30 ------   XRT s/c night exit.
-  21:03:00 ------   XRT SAA entry.
-  21:09:30 ------   XRT exiting from twilight.
 S-pole sequence.
-  22:15:00 -- s/c pointing to the South pole (-11,-955)
-  22:19:30 -- test sequence started (until ~22:33).
  
  -  -----------------------------------------------------------------------------------------------------------------------------------------------
  
-  1024x1024 pix, 2" resol., Full-Sun, Ti-poly and C-poly long/short 
  exposures.
  
-  256x256 pix, 2" resol., every 10 sec on the center FOV, 
  Ti-poly + G-band(VLS close).
  
-  1024x1024 pix, 2" resol., every 60 sec, Full-Sun, Ti-poly and C-poly.
  
-   detailed parameters of the sequence (XOB#1A30). 
  
-  -----------------------------------------------------------------------------------------------------------------------------------------------
  
 
-  22:22:30 ------   XRT entering twilight zone.
-  22:32:00 ------   XRT s/c night entry.
-  22:32:30 ------   pointing changed to AR12132.
-  22:38:30 ------   XRT s/c night exit.
-  22:40:30 ------   XRT SAA entry.
-  22:48:00 ------   XRT exiting from twilight.
 3. Results of the test observation.
 3.1 Sunset light curves
-  The same exposure time was used for polar- and limb(equator)- pointings.
It turned out that the Ti-poly 250ms was too short for the polar pointings,
where no active region included in the FOV. Low signal levels resulted in 
large fluctuation in the Ti-poly light curves.
-  The re-poining schedule was tight on the day of the measurement(8-Aug).
The pointing change (to the next observation) turned out a little too early
(30 sec to 1 min after the s/c night) and thus the light curves were 
truncated before the spacecraft completely enters the night.
 at the time of the N-pole pointing.
 
 at the time of the E-limb pointing.
 
 at the time of the S-pole pointing.
 
 3.2 Stray light images
Ti-poly stray-light images 
(4 second exp.) movie.
 
C-poly stray-light images 
(4 second exp.) movie.
 
Ti-poly stray-light images 
(1.4 second exp.) movie.
 
C-poly stray-light images 
(1.4 second exp.) movie.
 
Ti-poly stray-light images 
(4 second exp.) movie.
 
C-poly stray-light images 
(4 second exp.) movie.
 
 3.3 Image correction
| BEFORE [synoptic (double) composite image] | AFTER [stray light image (prep-ed) subtracted] | 
|  |  | 
| BEFORE [(double) composite image before twilight] | AFTER [stray light image (prep-ed) subtracted] | 
|  |  | 
| BEFORE [(double) composite image before twilight] | AFTER [stray light image (prep-ed) subtracted] | 
|  |  | 
| BEFORE [(double) composite image before twilight] | AFTER [stray light image (prep-ed) subtracted] | 
|  |  | 
| BEFORE [(double) composite image before twilight] | AFTER [stray light image (prep-ed) subtracted] | 
|  |  | 
| BEFORE [(double) composite image] | AFTER [stray light image (prep-ed) subtracted] | 
|  |  |