SECCHI/HI Level-2 files from SwRI

C. E. DeForest, March 2015

The L2 data from SwRI 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.


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 (

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