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Planetary observations, moving target
I have some solar system imaging. How do I reduce moving target images?
Member, Institute_Staff, Moderator_DrizzlePac
edited December 2014
Unfortunately, the pipeline will sometimes attempt to combine Solar System images as if they were fixed targets. It uses the World Coordinate System (WCS) info in the image header to align the images, which doesn't work for moving targets -- it will generally reject the target along with cosmic rays, etc. So the archival "drz" image is often not useful. The pipeline will recognize a moving target observations with the keyword MTFLAG=TRUE, and then I think it replicates the WCS of the first image into all the other images in the visit. This might work sometimes, but I think it might not recognize dithers, so still do a bad combination. So offline I usually drizzle each dither point separately, centering on the target itself. Then I can easily stack as many dithers or visits as I want to make the deepest and cleanest image possible. This works for targets that don't change between exposures (unresolved comets or asteroids), so for fast-rotating planets I usually generate single-drizzled images with no combination. I might run a single-image cosmic ray rejection algorithm like LACosmic, but often the exposures are so short for bright planets that there might be little to no CR contamination in the first place. We recently created a Planet Pipeline that creates the latter (single CR-clean images) for moving target images from all HST cameras -- watch for them as High Level Science Products (HLSP) when you do archive retrievals.