XRT HOWTO --- Monitor and Report on CCD Spot Creation

N.Narukage & M.Weber; 2008-Aug-15
Edited P. Grigis; 2010-Nov-09

Responsibility

This is an important point: The J-side (especially Shimojo-san and Narukage-san) currently have responsibility for officially monitoring and reporting the spot status after each bakeout. This HOWTO is provided for the following reasons:

To document the procedure and make it available to the XRT-CO Team.
To enable other team members to act as back-up personnel to perform the analysis.

Overview

CCD bakeouts are performed every 3 to 4 weeks to mitigate the accumulation of the contamination layer. There is a concern about the formation of spots on the CCD, so we have a monitoring policy. A set of "quadrant" images are taken immediately after every bakeout, and this data is used to produce a spot map. The new spot map is compared against the previous map to determine if any new spots are formed. There is some imprecision in this method, so there is a small, symmetric distribution of pixels that show the apparent addition and subtraction of spots. This analysis is quantified and distributed to the "xrt_co" email list in a report. It is usually reviewed and discussed at the subsequent XRT-CO weekly telecon.

This HOWTO explains how to run the spot analysis software so that you can generate the report. You can use this example of a report as your template.

Procedure

Determine the start (starttm) and stop time (stoptm) around the quadrant data.
Login to xrtco@xrtco.Note: you need to have X-display connection enabled for the IDL program to work. Login to xrtco with the "ssh -Y" option.
cd ~xrtco/lib/narukage/spot_check
Edit the quadrant.txt file.
- Each line corresponds to a bakeout and associated quadrant images. Add a new line for a new set of quadrant data.
- The first dimension of the quadrant array is the bakeout ID number.
  E.g., for the 13th bakeout, it would look like quadrant[13,*].
- The times should be the start and stop times of the quadrant data, but rounded wider by a little bit. Use:
  [starttm - (~ 1 minute), stoptm + (~ 2 minutes].
  Be careful to only catch the quadrant data in your time window!
- Here is what the line looked for the 13th bakeout:
  quadrant[13,*] = ['2008/08/06 18:35:00', '2008/08/06 19:15:00']
Start sswidl.
IDL> xrt_spot_check, bakeoutID, /outf [, ec_index=nn]
- where bakeoutID is the same number you put in the quadrant array in the quadrant.txt file.
- The /outf keyword will cause the XXth_bake_spot_data.genx file to be produced, which is the spotmap array. HOWEVER, the file will be produced in a DIFFERENT directory: ~xrtco/lib/spot_detect. (This other directory is Shimojo-san's version of spot software. However, Narukage-san's directory has the wrapper code, so we work there.)
- The ec_index=nn keyword is optional. It may be used to specify the exposure duration (as its index number) of the quadrant data. Sometimes, we have taken the quadrant data with various exposure durations, and this keyword is used to indicate which duration is to be analyzed. Currently, the default choice is 44 ms if the keyword is not invoked.
What will happen:
- It will take about a minute for the program to run. It takes time for it to deal with several graphic displays.
- There will be several display windows opened up, and they will process for a while.
- You will see displays for the spotmap.
- You will see a display of the difference map.
- You will see a display of a rebinned difference map. This will automatically be saved into the working directory as the file spot_report.gif.
- Various statistics will be printed to the command line.
Assess whether new spots have been formed. If the percentages of white and black pixels in the difference image are symmetric and small, then you may conclude that no new spots have formed.
Prepare the Spot Check Report.
- You may use a previous example as a template for the report.
- You use the spot_report.gif file to illustrate the rebinned difference map.
- You use the bakeout information and the statistical output of xrt_spot_check.pro to fill in the table row.
Send the Report file to the "xrt_co" email list. Include a summary statement of your assessment whether new spots have been formed.
Be prepared to discuss this result on email and at the next XRT Weekly telecon.