Time variability of Y-band fringing has been investigated sufficiently to see whether OBSTAC must be instructed to take a minimum number of consecutive images in Y band, such that a temporally local fringe frame can always be constructed.

This should also be investigated for z-band.

Cal-G6 goal is to bring fringe residuals to be invisible to the eye.


  • Software for basic image processing and to mask bright objects.
  • Software to create median fringe frame and scale and subtract them from individual images.


The time variability will be investigated under three circumstances:
  • Consistency within a single photometric night
  • Consistency between photometric nights
  • Consistency between photometric and nonphotometric nights

The minimum number of frames required to construct a useful fringe frame will also be measured.

The basic dataset is 10 dithered observations in the Y-band (z-band) with the survey exposure times. They should be obtained:
  1. Near the start and end of observations on a single photometric night
  2. At some time on at least one other photometric night
  3. At some time on at least one non-photometric (but 'useful') night
The analysis steps are:
  • Process each set of images to create a fringe frame (bias subtract, overscan, corrected flat field, mask bright objects)
  • Scale and subtract the fringe constructed from each dataset
  • Scale and subtract each fringe frame from the other datasets
  • Use the standard DESDM tool (or SExtractor by itself) to fit and subtract the large-scale background
  • Measure amplitude of residual fringing.
  • Repeat measurements with smaller numbers of files to determine minimum number of exposures required to construct the fringe frame


Analysis relevant to this requirement is available on this wiki page: Fringing


The fractional contribution of the fringing on scales of <=20" should be less than 10% of the shot noise. (Think about further)


If the fringing correction is time variable, enforce a minimum number of Y-band (z-band) exposures in OBSTAC.