IPAC 2MASS Working Group Meeting #94 Minutes

IPAC 2MASS Working Group Meeting #94 Minutes, 5/14/96

Attendees: R. Beck, R. Cutri, T. Evans, J. Fowler, L. Fullmer, D. Kirkpatrick, G. Kopan, G. Laughlin, B. Light, C. Lonsdale, H. McCallon, J. White

AGENDA

  1. Obs/IPAC Interface Document Rev. J
  2. Sparc Benchmark Suite
  3. Anti-persistence Study

DISCUSSION

  1. Obs/IPAC Interface Document Rev. J -- J. White reported that Rev. J of the Observatory/IPAC Interface Document is ready for signoff, which is hoped to occur by the end of this week. The definitions contained in this document are mutually agreeable on all sides and appear to be consistent with IPAC's requirements for processing the survey data, and therefore the TAPELOAD code is being written to conform with this version.

  2. Sparc Benchmark Suite -- G. Kopan reported that he has prepared a benchmark suite for use in calibrating a 4-CPU Sparc 3000 against lugosi. The suite involves running the currently delivered version of PIXCAL/DFLAT/RDFRAME/FREXAS, the prototype coadder, and KAMPHOT. Four pairs of scans are processed, one pair per CPU. Lugosi runs one pair in 2 hours on one CPU; it also runs all four pairs in 2 hours, using 4 CPUs. Since we apparently cannot get a 4-CPU Sparc 3000 as a loaner, and since Gene feels that it is quite important that a 4-CPU machine be used, he has prepared a tar file and placed it in the ftp area for the Sun Benchmark division to download, run, and send back the output files.

  3. Anti-persistence Study -- J. Fowler reported on the anti-persistence study he is conducting with help from G. Kopan, R. Cutri, and R. Beck. Selected pixel stacks have been studied via the latest debug output from DFLAT. The effect of very bright objects is a little different from what had been anticipated; instead of merely requiring more trimming before averaging, the stack of values is biased in a way that cannot be fixed by any symmetrical trimming. On the other hand, asymmetrical trimming has been found to be a very dangerous practice in the past, so if it is to be used, considerable caution will be required.

    J. Fowler and G. Kopan have developed a trial method for attempting asymmetrical trimming, known as "recursive median-distance rejection". This works as follows: The value farthest from the median is rejected; the median is recomputed; the value farthest from the new median is rejected, and the median is again recomputed; this is continued until half of the values in the stack have been rejected, and then the remaining values are averaged (the number of rejections could be a parameter, but currently we have been trimming about half of the values, 25% from the high end and 25% from the low end). This appears to be stable for the pixel values we have seen, and should be a more robust way to trim before averaging. J. Fowler will develop a testbed and try this algorithm out; if it appears promising, it will be coded into DFLAT and tried on scans known to produce visible anti-persistence artifacts in coadded images.

    A news item related to PIXCAL/DFLAT was pointed out by R. Cutri: the PIXCAL/DFLAT SDS has been signed off. Roc obtained the signature of the cognizant science team member R. Elston during a recent collaborative observing trip.