[daip] PCCOR suggestion.

R. Craig Walker cwalker at nrao.edu
Sun Jul 1 01:35:07 EDT 2007

At 43 GHz, I like to select a segment of time when the phases are linear
at all sites for the reference time for PCCOR (and VLBAPCOR).  That is
often less than a minute, and a small fraction of the scan.  I presume
that the fringe fit embedded in PCCOR will work better with that.  But I
keep bumping up against the problem that PCCOR insists that the period
used contain a PC table entry.  Since those entries are only once every 2
minutes (or one per scan for shorter scans), this can be problematic and
has forced me to shift to another reference time interval in several
recent observations.

My suggestion is that PCCOR relax the requirement that the PC table entry
be in the reference time interval but rather, when there isn't one
available in that interval, use the one nearest in time that is still in
the same scan (or perhaps interpolate).  The PC data basically don't
change significantly between entries in the same scan since they are
mainly sensitive to the temperatures of the cables and the cable wrap
position.  The temperatures change slowly, and the wrap only changes
quickly between scans.  So PC data from nearby in the same scan is
essentially just as valid as PC data from within the chosen interval.



    R. Craig Walker            Array Operations Center
    cwalker at nrao.edu           National Radio Astronomy Observatory
    Phone  505 835 7247        P. O. Box O
    Fax    505 835 7027        Socorro NM 87801   USA

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