Level 1 (Calibrated SOT-FG Data)

Creating Level 1 SOT-FG data requires applying standard calibration algorithms to each Level 0 FITS file. Such calibrations are performed using the fg_prep.pro routine distributed via SolarSoft. The source code for fg_prep.pro can be found at this link.

In creating the Level 1 FITS header, fg_prep.pro will insert lines into the HISTORY fields that detail the specific calibration steps that were taken. As indicated below, several SolarSoft databases ("SSWDB's") are used.

The calibration process involves the following steps:

  • The fg_prep.pro routine first identifies whether the input file contains a BFI or NFI simple filtergram image, or an NFI Dopplergram, magnetogram, or Stokes polarimetric image.

  • Next, camera readout issues (e.g. missing rows at center) are corrected by calling fg_shift_pix.pro.

  • Next, dark current and dark pedestal are subtracted by calling fg_dark_sub.pro, which employs the dark-frame database stored in $SSWDB/hinode/sot/darks.

  • Next, flat-fielding is applied by calling fg_flatfield.pro, unless the image is an NFI Dopplergram or a magnetogram. The flat-field database available via $SSWDB/hinode/sot/flats is used.

  • Next, bad pixels due to radiation-belt or cosmic-ray spikes or streaks are corrected by calling fg_bad_pix.pro.

  • Next, the pointing keywords in the FITS headers are updated using sot_fix_pointing.pro. These updates are based on a post-observation alignment database available via $SSWDB/hinode/gen/sot_corr_db_corrected, which incorporates pointing information from the spacecraft's ultra-fine sun sensor combined with periodic alignment observations taken by the three Hinode instruments, and cross correlations between SOT-FG (Ca II H, G band, and magnetogram images) and SDO (AIA 1700 Å, HMI continuum, and HMI magnetogram images, respectively).

  • Lastly, the roll-angle and plate-scale keywords in the FITS headers are updated using sot_fix_roll_scale.pro. These updates are based on mission-averaged corrections and are the same for all images.


  • SOT-FG Level 1 files use the same filename convention as the Level 0 data files. Refer to this section for an explanation of the file-naming convention. The processing level is identified by the DATA_LEV keyword in the FITS header.

  • In some instances, SOT-FG Level 1 data are unchanged from their associated Level 0 files. For example, a Level 0 Na I D magnetogram image having no camera readout issues and no bad pixels will only have its header keywords updated, and there will be no change to the data itself.