For a given noise level N, the
SNR in Stokes V is always smaller than in Stokes I because
the circular polarization signal is smaller than the intensity
signal. As an example, take
and
(these values
correspond to the profiles depicted in Fig. 4). The SNR in
the continuum intensity is
.
The SNR in Stokes V is only
.
The minimum detectable
polarization signal (the polarimetric sensitivity) is usually
estimated from the noise of the observations.
However, the
important quantity determining the reliability of the
inferred magnetic field is the SNR in Stokes V.
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