IPAC 2MASS Working Group Meeting #97 Minutes

IPAC 2MASS Working Group Meeting #97 Minutes 6/18/96

Attendees: R. Beck, R. Cutri, T. Evans, J. Fowler, T. Jarrett, D. Kirkpatrick, G. Kopan, K. Lester, B. Light, H. McCallon, J. White


  1. Extended Source CDR Runthrough
  2. Flattening Tests and Saturation Thresholds
  3. PCP Disk Requirements
  4. Meeting Schedule


  1. Extended Source CDR Runthrough -- T. Jarrett reported that the Extended Source CDR runthrough will be held this Friday, but the time of day had not yet been settled. T. Chester will be requested to set the schedule and notify the working group.

  2. Flattening Tests and Saturation Thresholds -- The current flattening tests are exercising pixcal, dflat, rdframe, and frexas as an integrated processor. The main goal is to study the effects of varying the flattening control parameters. Nine scans are in the test set, which is made up of one low density, one high density, and one galactic center scan in each band. The trimmed averaging is now able to use a hybrid method in which some number of "Recursive Median Distance Rejection" trims are done (given by the parameter NRMDR), followed by a trimming of some other number of points off each end of the remaining range of pixel samples (given by the parameter NTrim). Each scan will be done with three pairs of NRMDR and NTrim values:

    (a.) NRMDR = 0, NTrim = 10 amounts to the previous symmetric trimmed averaging that could not eliminate the anti-persistence artifacts;

    (b.) NRMDR = 20, NTrim = 0 amounts to the asymmetric trimming which did succeed in eliminating anti-persistence artifacts, but which may degrade low density scans without persistence;

    (c.) NRMDR = 10, NTrim = 5, which will allow some asymmetric trimming where needed but should not degrade cases where it's not needed as much as NRMDR = 20, followed by symmetric trimming of the remaining samples.

    The tests also include the new saturation processing. The first run indicates that something therein is not working, as no saturated pixels were reported by dflat, whereas it is known that an extremely bright object is in the scan. J. White and J. Fowler will examine the code and interfaces to determine where the problem lies. Preliminary work in this vein has shown that the saturation threshold may not be appropriate for the 2-byte integer values involved in the raw data. These are produced at the observatory as unsigned 16-bit integers, but the 16-bit integers in Sun FORTRAN are exclusively signed, necessitating special handling at the wrap-around point of 32767. Since the design no longer involves testing for exact (integer) equality of a pixel value with a saturation threshold (because thresholding at lower values to avoid significant nonlinearity has been adopted), the testing can be done in the REAL*4 domain. R. Cutri requested that the threshold for now be 3.0e4, since the indications are that hard saturation occurs somewhere between 3.3e4 and 4.0e4, and significant nonlinearity appears to set in around 3.0e4 in each band.

  3. PCP Disk Requirements -- R. Beck reported that he prefers to use nine 9GB disk drives per production machine rather than 20 4GB drives, where the latter has been recently suggested as a way around the reliability problems of the 9GB drives (with failure rates reported within IPAC to be about 10% per year). The 4GB drives are said to be more reliable and could satisfy the PCP design (see last week's minutes), but are more expensive per GB. Since the use of 4GB drives would require more than twice the number of drives, they would have to have less than half the failure rate, assuming similar duty cycles. The point was made that the use of 9GB drives with spares would probably be less expensive that the use of 4GB drives, also requiring some spares, although the final pricing information is not yet available.

  4. Meeting Schedule -- J. Fowler reported that next week's Working Group Meeting will be cancelled because of the need to prepare for the next day's Extended Source CDR and the fact that the runthrough will have been held already on Friday. He will then be on vacation from June 27 through July 15, so that the next two Working Group Meetings will not be held formally.