sxtmov) 30-sep-2009 (AkT) Added Level2_WL. --> A Guide to the YLA

Summary of the Beta-release

On the present release, the YLA includes Level 0 (raw), Level 1 (corrected and assembled) and Level 2 (corrected and composited) data products for the SXT. The Level 1 and 2 data products have been corrected as fully as possible for instrumental effects such as dark signal and visible straylight. Level 1 includes both full frame (FFI) and assembled partial frame (PFI) data in floating point format. Level 1 products include every usable image, even if most of the frame may be missing due to TLM dropout. Level 2 data products include only FFIs taken with the SXT thin (1200 A aluminum (Al.1) and Al/Mg/Mn composite (AlMg) filters. Level 2 FFI images have been de-scattered by deconvolution of the SXT point spread function and have been corrected for telescope vignetting. SXT Level 1 and 2 data products are in instrument units (DN/sec/pixel). Conversion to physical units requires knowledge or assumption about the solar differential emission measure and the use of software such as, e.g., sxt_teem.pro.

We have created SXT data products in both YOHKOH-specific (XDA) and FITS formats. The XDA format is convenient for analysis with existing SSW/YOHKOH software that runs under IDL. The more general FITS format enables use of advanced SSW applications including the SSW mapping software by Zarro et. al. FITS products do not specifically require IDL to read and view images.

Level 0 data for all Yohkoh instruments and Level 1 full-frame images for SXT are also available via the Virtual Solar Observatory. For Level 2 browse images, the SXT movie maker service is available to create the customized movies of 2-composite FFIs, of your own!

Service of data searching, quick-looking, or custom archiving is not available in this beta-release. For the purpose of helping to find suitable datasets, the SXT Observing Logs Inquiry Form is available.

Here is a list of data products available in the YLA at this time.

XDA Format:
    Level 0 (One file per YOHKOH orbit)
        Complete raw, reformatted data for all YOHKOH instruments.
    Level 1 (One file per calendar day)
        All usable PFIs, observing regions assembled.
        All usable FFIs.
    Level 2 (One file per calendar day)
        Two-exposure composite FFIs.
        Two-exposure uncertainty arrays.
        Three-exposure composite FFIs (longer exposures).
        Three-exposure uncertainty arrays.

FITS Format (One file per image):
    Level 0     Not applicable.
    Level 1
        All usable PFIs, observing regions assembled.
        All usable FFIs.
    Level 2
        Two-exposure composite FFIs.
        Two-exposure uncertainty arrays.
        Three-exposure composite FFIs (longer exposures).
        Three-exposure uncertainty arrays.
        Two-exposure browse FFIs.
        Three-exposure browse FFIs.


Cautions and disclaimers:
0.  Exposures comprising Level 2 composite images may be taken up to +/- 11
  minutes apart.  Beware of solar changes between exposures.  For study of
  specific events or periods it is advisable to examine the Level 1 data
  which often include many images that, for one reason or another, didn't
  make it to level 2.
1.  Correction for CCD saturation in Level 2 products is not perfect in
  many highly saturated images.  Flare and eclipse images are not well
  corrected because of caution 0.
2.  This a beta release, please be alert for and report problems with the
  data products.  Screening to remove bad images isn't complete.
3.  There are uncorrected problems with the YOHKOH attitude database late
  in the mission, particularly in 2001.
4.  After 14-Nov-1992 straylight correction of the thin Aluminum images
  isn't perfect.  This has a minor effect for the analysis of bright
  features but causes intensity uncertainty of faint regions -- which is not
  reflected in the uncertainty arrays.  The best looking movies will be made
  from the AlMg filter, half-resolution, images.


Data description and Links

Level_0 data

They are raw data files in the Yohkoh format, readable with a SolarSoft procedure. They were taken for each satellite orbit, and organized in the weekly directories.
An example of the file name: sfr920720.1502 
 sfr: A prefix for SXT Full Frame (whole sun) Images.  
      Other prefixes --- spr : SXT Partial Frame Images
                         hda : HXT data
                         bda : BCS data
                         wda : WBS data
                         ada, cba : for calibration purpose. 
 920720.1502 : date and approximate time (yymmdd.hhmm) at which 
               the satellite started observation in the orbit.

http://solar.physics.montana.edu/ylegacy/weekdirs/
ftp://solar.physics.montana.edu/pub/yoarch/weekdirs/

Level_1 products

Level 1 products include every usable solar image. All calibration images and detected problematic frames are eliminated. Basic calibration such as dark and leak(due to filter failure) corrections is done. The 'low-8bit images' taken with the optical filter are restored as far as the compressed counterparts are available. The observing regions taken in partial frame images are assembled to show the whole region of interest.

Level_2 products

SXT composite images combine 2 or 3 long and short exposures to increase dynamic range and remove detector saturation. Each composite image has a related uncertainty image which provides the statistical error for each pixel. SXT browse images are made from the composites and are comparable to the now-familiar SXT movies. They are logarithmic(safe_log10) and byte(8-bit) scaled, cleaned of SAA and cosmic ray spikes, and adjusted so that images from the 2 SXT thin filters look similar. Browse images are cosmetically appealing but are not appropriate for quantitative analysis. Level 2 data products only use complete or nearly-complete images. Only the SXT browse images have been co-aligned. Other SXT images may be readily co-aligned with existing SSW mapping tools.

The coaligned white light images are now available. They are only available in FITS format.



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