Next: Averaging
Up: Amplitude and phase
Previous: Closure relationships
Contents
Index
Statistics
It is worth noting that while the noise in the real and imaginary
parts of the visibilities follows gaussian statistics, with a null
expected value, the amplitude and phase do not, especially at low
signaltonoise. The amplitude in particular is by definition
positively biased, i.e. has a nonnull expected value even in the
absence of signal.
Figure 1:
Probability distribution for the amplitude (Top) and real part (Middle) of the visibilities for various signaltonoise ratio (0,1,2,3,5,10). Adapted from Wrobel and Walker (1999). Bottom: Expected value for the amplitude as a function of signal strength (in unit of
) for the amplitude (plain curve) and real part (dashed curve).

Figure 1 shows the probability distribution for the
amplitude and real part of the visibilities for various
signaltonoise ratios and compares the expected values for both
quantities. Figure 2 shows the probability
distribution for the phase. It follows that at low signaltonoise a
detection is more easily seen on the phase than on the amplitude.
Figure 2:
Probability distribution for the phase of the visibilites for various
signaltonoise ratio (0,1,2,3,5). Adapted from Wrobel and Walker (1999).

Next: Averaging
Up: Amplitude and phase
Previous: Closure relationships
Contents
Index
Gildas manager
20220117