Synoptic study made with the XRT synoptic composite images.

(by Aki Takeda, 30, September 2014)

1. Statistics of the XRT synoptic composite images.

These numbers are based on the synoptic composite images processed at MSU for 1-Nov-2006 through 31-Aug-2014.

Total number of synoptic images 18149
Open/Al-mesh filter images 5379
Open/Ti-poly filter images 6177
Open/Thick-Al filter images 33
Open/Thick-Be filter images 21
Al-poly/Open filter images 2973
C-poly/Open filter images 652
Thin-Be/Open filter images 2245
Med-Be/Open filter images 133
Med-Al/Open filter images 176
Al-poly/Ti-poly filter images 326
C-poly/Ti-poly filter images 176
Number of full-resolution images 6309
Number of half-resolution images 11840

[MEMO 1] Major periods with no data.

[MEMO 2] It is noticed that the "official" synoptic image archive (by SAO in Sep. 2014) contains significantly lower number of images than the MSU version. The following study was made with the images in the MSU archive.

2. Measurement of the Al-mesh and Ti-poly signals.

According to the above statistics, the Al-mesh and Ti-poly images turn out to be suitable for the studies over a long time range.

[Steps of image processing]

  1. Normalize image size to 512x512 (adjust intensities accordingly).
  2. Take co-alignment (with Keiji's latest DB).
  3. Eliminate bad images.
  4. Find available pairs of Al-mesh and Ti-poly images.
  5. Masking pixels outside 1.10 solar radius.
  6. Sum up the intensities.

[Sample images]

a slightly off-centered image.
Disk Center is not located
at the image center.		 DC was shifted to the image
center and the area outside
1.1 R_sol was masked.		 example of small solar disk
taken near apogee.

[some test study]

[intensity plots]

The GOES/XRS fluxes are corrected based on a NGDC note, http://www.ngdc.noaa.gov/stp/GOES/doc/GOES_XRS_readme.pdf.
The white lines show the values before correction.

Ti-poly intensities are affected by the pre-filter failure occurred on 9-May-2012. The correction is possible with the use of stray-light images obtained in the 2014 eclipse season, but the following "fudge factor" needs to be applied taking account of the increasing trend of the stray-light intensity with time. 
[Ti-poly (corrected)] = [Ti-poly (original)] - [stray-light image 2014] * (fudge factor)
"fudge factor" : 0.5 9-May-2012 through 14-Aug-2012
0.7 15-Aug-2012 through 31-Dec-2012
1.0 1-Jan-2013 and after
In the forllowing plots for 2012, the blue line shows Ti-poly signals with the fudge factor applied, white line shows signals before correction.

Plots for other years

2007
2008
2009
2010
2013
2014

The signals in 2007 and early 2008 behaves weird, probably due to the CCD contamination problem. Since Feb-2008 when regular CCD bakeout operation started, the CCD entered a different stage of sensitivity which continues to be the same until present. Therefore, we should not use the data before Feb-2008 for the irradiance study. We will start from 21-Mar-2008, when Al-mesh and Ti-poly pairs started to be taken regularly.

Signal movie for all years
Temperature and EM movie for all years

3. Filter-Ratio Temperatures and Emission Measures.

Filter-ratio curves for the Ti-poly and Al-mesh filter pairs

The GOES/XRS temperatures (green) and emission measures (light green) are corrected based on a NGDC note,
http://www.ngdc.noaa.gov/stp/GOES/doc/GOES_XRS_readme.pdf. The white line shows the values before correction.


The white lines show the Te and EM values calculated with UNCORRECTED Ti-poly intnsities with stray-light images.


4. XRT Irradiance

Based on the derived temperatures and emission measures, we can calulate the solar flux (W/m^2) received at the earth orbit, using Chanti atmic database ver 7.13. The flux was integrated for the wavelength band 1-8A, same as the GOES/XRS low energy band flux. For comparison, XRT irradiance for integrated for 1-10A was also calcuated.