SECCHI/HI Level-2 files from SwRI
C. E. DeForest, March 2015
The L2 data from
exist in FITS form for both STEREO-A HI-1 and STEREO-A
HI-2, through the end of 2013. They are photometric images of feature-excess
brightness (radiance) in Thomson scattered light, extracted from the original
images. The L1 photometry was performed using the standard SECCHI_PREP
pipeline. Subsequent processing was as described initially in by DeForest,
Howard & Tappin 2011
(Astrophys. J. 738, 103).
Like the L1 data, the images are calibrated in "mean solar radiance" units
(B_\odot or B_s), which consist of the solar intensity divided by its apparent
size in steradians. A paper is in work for Astrophys. J. describing the
processing in more detail.
Additional information can be found in the individual subdirectories.
ARTIFACTS TO AVOID
The HI data, particularly the HI-2 data, contain many artifacts that
must be distinguished visually from the actual data. A non-exclusive
list follows. In case of doubt, you can contact the instrument team,
Craig DeForest, or Tim Howard
- Glint from the interior of the instrument affects the HI-1 images.
Planets moving outside the field of view glint off the optics and
produce strange circular artifacts.
- "Telegraph stars" and remnant vertical stripes are present in all
images, from detector nonlinearity effects that manifest with the
brightest stars. These are due to nonlinearity in the CCD, the exact
nature of which is still being discussed. The result is that bright
stars have variable reported brightness as they cross the field of
view. Furthermore, the brightness is systematically underreported,
which confuses the (non-SwRI) destreaking algorithm.
- "Bowtie" artifacts are present near bright planets, in the HI-2
data and the HI-1 L2M data. These are due to interaction between each
bright planet's motion and the motion filter.
- Large blobby artifacts when the galaxy is in the field of view. The
Milky Way is quite bright and also spiky. This produces enough
telegraph stars in each small region of the sky, to confuse the
background finding algorithm, leaving positive-going remnants. Data
acquired during the passage of the Milky Way through the field of view
are essentially unusable.
- The HI-2 data, and some HI-1 data, have flashing vertical stripes
that are generated by CCD saturation and blooming during the passage
of planets and a very few bright stars (such as Vega) across the field
- The photometric zero-point shifts slightly across each image,
particularly in the HI-2 L2 sequence, with an amplitude of approximately
Name Last modified Size
Parent Directory -
a/ 2015-02-23 23:57 -