What steps are taken to produce the mosaics? What files are available?
In the current definition, mosaic processing requires three steps. First, the data for each visit are combined with the standard multidrizzle processing (the same used for Level 2 combined data) in order to identify cosmic rays and other blemishes. The pixels in each exposure that are flagged will not be used in further combinations. Second, the images are aligned across visits by matching source catalogs for each visit. The alignment is done using the same multifilter images that are also used to identify objects for the source lists. This step is required because images can only be successfully combined if they are registered to a relative accuracy of a fraction of a pixel (the goal is 0.1 pixels), much better than the residual uncertainty in the absolute astrometry even for images that have been astrometrically adjusted. Third, the images for each filter are projected onto the final pixel grid using multidrizzle, with the adjusted astrometry but without additional processing to remo
