10.2.4 Estimate of the thermal noise

The resulting thermal noise is given by

$$1 \sigma = \frac{2 k T_{sys}}{\eta A \sqrt{\Delta \nu \times t}} (\mathrm{K})$$ (10.13)

where k is the Boltzmann's constant, A is the geometric collecting area of the telescope, $\eta$ the global efficiency factor (including decorrelation, quantization, etc...), $\Delta\nu$ the bandwidth in use and t the integration time. The resulting phase noise is inversely proportional to the signal to noise ratio.