I'm working with some New Horizons MVIC/Ralph data. I'm taking the red, blue, and NIR channel data and create a false colour image, like this: Pluto+Charon (PDS Label of Red Channel image, accessed from OPUS)

Because of the nature of the MVIC/Ralph instrument (offset long, skinny CCDs in a time-delay integration scan) the individual channels need alignment. I manually aligned the above image but I am looking to automate/script this process.

Luckily, the angular offset of each channel is known:

instrument FOVs

(PDS Label)

I tried to use this information to calculate how many pixels to move each layer for a different image (PDS Label). The image is 5024 x 7776 px and page 6 of Reuter et al. gives the single pixel FOV as 19.77 µrad. This translates to ~50582 px/rad. Each channel is separated by 0.037° (19.77 µrad x 32 px) + 0.070° $\to$ 1.854 mrad. I expected this to mean having to move each channel by ~94 px (50582 px/rad x 1.854 mrad). This is short by about 10-12 px still:

wrong offset

When applied to subsequent channels (in multiples) the 10-12 px offset remains constant.

What other factors could be at play here? I don't think it's the 12 dead pixels at the edge of each CCD as those are in the "other axis," but I could be wrong.

  • Reuter et al. "Ralph: A Visible/Infrared Imager for the New Horizons Pluto/Kuiper Belt Mission," Arxiv.org Link
  • $\begingroup$ There is more than meets the eye here, alignment of top limb of Pluto still yields misalignment at bottom limb! $\endgroup$ Feb 28, 2022 at 13:15


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