Fig. 4

a An example of a Level 1 image: a raw image before correction, taken at 08:01 on May 07, 2016, at a distance of 91,000 km with a sub-spacecraft latitude of − 10° and a longitude of 325°. b An example of a Level 2 image: a cleaned image of Fig. 4a after smear-like noise correction and flattening procedure. These corrections and procedures are described in the text