Calibration Access and Data Handbook

Generation from In-Orbit Data

The basic idea is to obtain a supersky flatfield by combining a large number of relatively object-free exposures of random fields. A similar approach has been used to obtain WFPC superflats (Ratanunga et al. 1994, APJ, 108, 2362). Most suitable datasets are data from default configurations, because the entire detector area is covered. The detailed analysis steps are

• fpn correction
• source identification
• cut out sources
• normalize images by average counts per pixel and stack images
• add stack of images
  • weighting with square root of avg. counts per pixel
  • take into account number of exposure per pixel
• fit bicubic spline surface to obtain new large scale flatfield

The LargeScaleSens files can locally be validated using celestial objects in calibration offset pointings.