One subtlety is that the noise is unaffected by the atmospheric decorrelation, in contrast with the signal, because noise is a random process as the turbulence phase noise.
But the conversion factor,
, is applied to the data that can
contain signal as well as noise. Any attempt to measure the noise rms on
visibilities or imaged data will thus results in a standard deviation
larger than the one given in Eq. 6 by a factor
. So when we estimate the noise level of an interferometer, we need
to take into account the interferometric conversion factor that depends on
the typical weather conditions (i.e., the atmospheric rms phase
noise). This gives