= Interferometric radiometer equation
{title2=$\sigma_S=\frac{\mathrm{SEFD}}{\sqrt{N(N-1)\Delta\nu t}}$}
For $N$ equal <antennas>, weak-source independent receiver noise, natural weighting and total on-source time $t$, the point-source rms in one <polarization of waves> is the displayed value. There are $N(N-1)/2$ independent cross-correlation baselines, each with real-component error $\mathrm{SEFD}/\sqrt{2\Delta\nu t}$. Combining $n_{\rm pol}$ independent <polarization of waves> estimates reduces the rms by $\sqrt{n_{\rm pol}}$. Correlation losses divide the sensitivity by an efficiency factor; weighting, flagging and an extended source change the effective sensitivity.<Sensitivity by Joan Wrobel>[slides 7–12 and 20, baseline and image sensitivity]{ref}
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