One may simply wish to average several channels to increase the signal to noise ratio (use tasks UV_COMPRESS and UV_AVERAGE).
For sources with circular symmetry it may be necessary to obtain the
variation of amplitude with antenna spacing, in order to compare the
amplitude data with models. For this purpose, with task UV_CIRCLE one takes the mean of all the visibilities in
concentric rings in the plane. The output has the format of a
table (except that all
's are zero), and may be plotted with
UVALL (fig. 14.5).
Use this sort of averaging with caution: the phase center must
accurately coincide with the source position or the amplitude of the
visibility average will decrease on long spacings (use UV_FIT
and UV_SHIFT).
One may also do this kind of averaging in separate sectors in the
plane, to check for asymmetries, provided the
plane is well
sampled (task UV_CUTS).