New PSF/Seeing Diagnostics

As of the week of 10/26/98, pipeline processing has incorporated a new and improved measure of PSF elongation. The older technique of looking at the image moment ratio was insensitive to diagonal elongation since it simply compared the width to height of the PSF's. Tom Jarrett's new code rotates the psf images, comparing image moments and solving for both the ratio of the minor to major axis and the position angle of the elongation. This gives an unbiased measure of PSF elongation independent of its rotation.

The QA web pages have been updated to provide a new diagnostic plot using this information, if present. In the Seeing Shape & Ratio Plot the Image Moment top panel has been replaced by the Minor/Major Axis Ratio. This ratio is constrained to be <= 1.0. The Image Axial Ratio middle panel has been replaced by the Position Angle of the major axis of the PSF. The bottom Seeing Shape panel is unchanged. Plots for nights which have not been processed with the new code will display the original diagnostic plot.

Typical new-style plot

Typical old-style plot

A sample run of this new PSF diagnostic was made on one of the recent northern focus tests (981017n):

For comparison, the older 2nd Moment ratio plot can be seen below:

The corresponding PSF images are displayed below:

Last updated 10/28/98 by R. Hurt