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.

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Copyright © 1997 The Association of Universities for Research in Astronomy, Inc. All Rights Reserved.


Harry Ferguson ferguson@stsci.edu 3/01/96