RFD discussion on initial PSF FWHM estimate, Dec. 15, 12:30pm PST
Currently, one of the configuration parameters is an initial estimate of the PSF FWHM (calibrate.initialPsf.fwhm). processCcd can fail if this is not set properly. This is problematic for two reasons:
- The LSST science pipeline needs to be completely automated and can’t depend on exposure-specific user input.
- The LSST config philosophy is that there is a one set configuration setup for a full (re)run of a dataset. If the initial PSF FWHM config parameter needs to change from visit to visit (because the seeing does change throughout the night), then this breaks our “one config only” philosophy.
Therefore, we need code that will automatically estimate the PSF FWHM. A few options on how to proceed have already been mentioned but no clear path has emerged. Therefore, we will have an RFD discussion on this topic. Note that this will impact how single frame processing (e.g., processCcd) works.
A couple of issues/ideas to keep in mind:
- can we use an iterative procedure starting with a delta function and looping through most of the single frame processing steps a couple of times until we converge on a good PSF
- the single-visit CR rejection algorithm requires an initial PSF estimate
- how to deal with contamination from galaxies and “junk” which will mess up the PSF estimate
- if we use an external catalog to select the stars then this will require more steps (i.e. astrometry, matching, etc.)
Product of the discussion:
- We want to converge on the path forward on how to implement an automated initial PSF estimation code
- Who will do the work, or which team
- What is the priority
- On what timescale should this work be completed
- RFD slot on Tuesday Dec. 15, 12:30pm PST
- bluejeans: ls.st/jmc
See also: Outline of main processCcd.py algorithm