XRT irradiance study --- returns!

Our method to derive solar soft X-ray irradiance

• Use a series of XRT full-sun synoptic composite images taken with Al_mesh and Al_poly filters (found in SCIA).
• Calculate filter-ratio Te and EM from the full-sun integrated signals (< 1.10 R_sol) from Al_mesh and Al_poly images.
• Calculate model solar spectrum using the derived Te and EM, assuming isothermal corona (with CHIANTI atomic DB/SW).
• Integrate the spectrum through a specified wavelength range. Typically, most effective range of the XRT filters (4-200A, or 5-60A). Or other instruments' observing range for comparison (1-8A with GOES/XRS, 0.4-20A with MinXSS, etc.).

IMPORTANT NOTE: To derive irradiance from XRT signals after May-2012(when the stray light started to appear), two types of corrections are required:

(1) Subtraction of stray light image from each X-ray images.
(2) Modify XRT response functions so that it reflects the appearance of the stray light.

This study only handles the correction (1), because we don't have the confident method yet for the correction (2).

More detailed procedure --- note for myself.

1. [find_amap_pairs.pro]
   Find Al_mesh and Al_poly image pairs taken within 5 minutes for each month.
   Eliminate pairs with bad images (missing frames, SAA, cosmic rays, saturations, etc.).
   Save file names.
   
2. [get_disksig_amap.pro]
   Read monthly pairs of Al_mesh & Al_poly images.
   Subtract stray light images from both filter images
   (cf: stray light images for the phase 2, Al_mesh and Al_poly).
   Mask outside 1.10 R_sol and get total intensities(signals).
   Save indexes and signals for each filter.
   
3. [sig2teemirrad.pro]
   From the pair of Al_mesh & Al_poly sinals, calculate filter-ratio Te and EM.
   Calculate solar spectrum of the isothermal plasma (with Te, EM=10e44cm^-3) with CHIANTI for the wavelength range of 0.05 to 300A, assuming elemental abundances ('corona' or 'hybrid').
   Calculate total spectral intensities within a specified wavelength range and adjust geometrical factor and observed EM to get the irradiance at 1 AU.

   -- Contents Summary of Generic File: /disk/yla/takeda/xrt_irradiance/teemirrad_v4_hybrid_201606.genx--
   .....  Data Section .....
   ** Structure MS_290034151011, 9 tags, length=506224, data length=502396:
      INDEX_AM        STRUCT    -> MS_290034151010 Array[58]
      TE              DOUBLE    Array[58]
      EM              DOUBLE    Array[58]
      IRRAD1_8        DOUBLE    Array[58]
      IRRAD1_10       DOUBLE    Array[58]
      IRRAD1_12       DOUBLE    Array[58]
      IRRAD04_20      DOUBLE    Array[58]
      IRRAD5_60       DOUBLE    Array[58]
      IRRAD4_200      DOUBLE    Array[58]
   -----------------------------------------------------------
   

4. [connect_monthly_irrad.pro]
   Connect monthly files to make a single time series for further processing.

XRT Synoptic Composite Images statistics.

XRT response functions and filter-ratios.

The calcualtion of model solar spectra was done with CHIANTI atomic DB & SW ver. 8.0.7. The elemental abundance files used in the calculation are as follows:

• coronal abundance : sun_coronal_1992_feldman_ext.abund
• hybrid abundance : sun_coronal_2012_schmelz_ext.abund
• photospheric abundance: sun_photospheric_2011_caffau.abund

XRT irradiance in 6 wavelength ranges.