- 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.
- 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.
- 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.
- 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.