2001 October 1-December 31 AIPS Quarterly Report

Distribution and Versions

The 31DEC01 version of AIPS, updated daily, was distributed 556 times, to about 475 sites, after December 2000. This version has now been frozen, in preparation for release in January 2002. A new evolving version that is updated daily, called 31DEC02, has been initiated.

Key Developments

• The move of the "midnight job" and the master version of AIPS to NRAO-Socorro is being done in conjunction with the initiation of the 31DEC02 version. This move was nearly complete at the end of December 2001, and is expected to be finished in January. At that time, the daily versions will be accessible by an ftp copy/update procedure that is run under the Unix "cvs" utility. This eliminates dependence on "secure shell" (ssh) copies, which appear to have been a significant impediment to some users in implementing the midnight job. In addition, it should eliminate the common failures of midnight jobs that have occurred when system managers on either end make modifications to ssh.
• The TECOR task, which applies global ionospheric corrections to VLBA data, has been extended to cover data sets crossing UT midnight (actually, UT 2300). Users now can apply corrections for multiple dates merely by specifying (and making available) multiple "IONEX" format files.
• Several modifications were made to FITLD in order to properly handle multiple frequency IDs (FQIDs) having the same frequency, frequency offsets from FQID number 1, and the proper comparison of tape bytes to AIPS bytes.
• Exercising the VLBAUTIL procedures for simplified VLBA data reduction revealed errors and inconsistencies in the help files and default parameters for several AIPS tasks. In some cases, modifications were made to default parameters in VLBAUTIL, while in other cases, help files were modified to correctly represent what tasks were actually doing. The main tasks affected were SNSMO and FRING (help files clarified), while procedures that were modified included VLBACALA, VLBASUBA, and VLBAFQS..
• IMAGR was modified to handle clean boxes from a BOXFILE more forgivingly, and to handle correctly a modification of flux limits with the TELL command during multi-field cleaning.
• COMB, which combines images in various ways, has had the `SUMM' option added in order to blank a pixel in the output image only if both input images are blank at that pixel; otherwise, it uses the value from the image whose pixel is not blanked, as in `MEAN.'
• A new procedure called FITDISK was added to enable AIPS files to be written out as disk files with default names, using appropriate interpretations of the file names inside AIPS. This enables multiple files to be written to disk using a simple "for" loop in POPS.
• An investigation was made of possible options to separate primary and subreflector errors in VLBA holography results. Mathematically, additional information/assumptions beyond the holographic measurements are requird to effect this separation.

Goals for Q1 2002

1. Continuing maintenance and user support.
2. Complete release of 31DEC01 version, and move of primary copy and midnight job to Socorro.
3. Complete comparison of FRING and KRING for fringe-fitting under various conditions.
4. Develop a data-editing task to use the VLA weather information now provided by FILLM.
5. Revise Cookbook Appendix C based on VLBAUTIL procedures and incorporating code changes.