characterizes the antenna hardware, i.e. it assumes perfect
atmospheric conditions or the use of autocorrelations, as in single-dish
measurements. In interferometric mode, the phase of the turbulent
atmosphere above each antenna of a given baseline has a random part that
causes an additional ``attenuation'' of the amplitude of the correlation. A
point source of 1Jy flux will appear as a source of
Jy flux if
we only use the
factor. This is called atmospheric decorrelation
and it depends on the weather during the observations.
However, the last calibration step of interferometric data is to measure a
point source of known flux to deduce the actual conversion factor,
, taking into account the atmospheric decorrelation that happens
during the observations. By definition of
, we yield
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(7) |
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(8) |