THEMIS uses the CDF (Common Data Format) for many L1 data products.
CDF is NOT the same as NetCDF, so programs such as
ncview will NOT work with Themis CDF files.
Download the L1 CDF files by first looking at the L0 64x64 pixel GIF previews.
Here are Matlab and Python functions I wrote to look at THEMIS ASI images to make movies and the like.