WFC3 Instrument Handbook for Cycle 24 . ... DN were measured using internal flat field exposures taken from Oct 2010 to June 2015 ( WFC3 ISR 2015-14 ). ... The intermediate reads are used by the WFC3 data pipeline to identify cosmic ray hits, similar to the use of CR-SPLITs in CCD observations. ... As discussed in Section 5.7.9 , the WFC3/IR detector exhibits image persistence, particularly during and following observations of targets that saturate the detector by more than the pixel full well depth. ...