[daip] AIPS image scaling effect

[Eric Greisen]

You should probably consider two effects that we have not mentioned.
One is across beam calibration.  Telescope beams vary in phase across
the beam as well as in amplitude.  The other concern is the
ionosphere.  The isoplanatic patch is likely to be less than 2 degrees
even at P band some of the time.

In fact, I had observations in the VLA A array in which the P band
images came out as about 6 spots from 2 5-minute snap shots.  This
means about 3 spots per 5 minutes at baselines much shorter than yours
and spread over an area much larger than 0.5 arc sec (in fact the beam
was 7 arc sec).  The ionosphere was particularly bad for my observing
run, but 0.5 arc sec is suddenly looking like much better agreement
than I was thinking previously.

Eric Greisen