45.5 Improvements to Calibration Reference Files

Several types of reference files and their associated calibration processes have been improved substantially. The following lists types of calibrations that may benefit from recalibration due to the improvements:

• Improved BLEV correction, as of February 1992. calwfp determines and removes odd and even column levels separately.
• Bias reference files for PC and WF were improved in August 1993: 40% lower noise than previously.
• Preflash reference files for PC and WF also improved in August 1993: noise was reduced by a factor of two.
• Since the WF/PC-1 darks were found to be time-variable (see WF/PC-1 Instrument Science Report 93-01), additional calibration observations were obtained and dark reference files generated for specific time intervals. There are now more than a dozen dark reference files for each camera, covering the time period July 1991 through November 1993. Please refer to the WWW Reference File Memo to identify the best dark to use for the data based on the date the science observation was taken (DATE-OBS keyword in .d0h file).
• Many new and improved flatfields were generated and installed in the Archive after the end of the WF/PC-1 mission (see sections "Choosing Among Available Flats" on page 45-15, and "Improving the Flatfield Correction" on page 46-15); the WWW Closure Flatfield and Reference file memos offer more details about these files and their use. Note that many of the early flatfields were generated from earthcals taken with a neutral density filter (F122M or F8ND); these flats can have residual intensity gradients of up to 20-30% across the field of view.