HDF version 2 noise properties
The attached figures compare the rms fluctuations of the sky background
measured in blank regions of the final drizzled images from version 1
and version 2 of the HDF data reduction. The images have been
successively binned 2x2, 3x3, up to 16x16 pixels to highlight
the fact that the images are smoother on pixel scales than
would be computed from a naive application of the CCD noise model.
This is because the image combination process produces correlations
between neighboring pixels.
The figures show the rms fluctuations divided by sqrt(N) where N
is 2 for 2x2 binning, 3 for 3x3 binning, etc. If the noise were
uncorrelated there would be no change in the rms with N.
The open circles show version 1 of the data, with the dashed line
showing the best estimate of the mean for N>6. The filled circles
show version 2 of the data, with the solid line corresponding to
the best estimate of the mean for N>6.
Copyright © 1997 The Association of Universities for
Research in Astronomy, Inc. All Rights Reserved.
Harry Ferguson email@example.com 3/01/96