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The system temperature is a summary of the noise added by the system. This
noise comes from 1) the receiver and the optics, 2) the emission of the
sky, and 3) the emission picked up by the secondary side lobes of the
telescope. It is usual to approximate it (in the
scale) with
![\begin{displaymath}
\ensuremath{T_\ensuremath{\mathrm{sys}}}= \frac{\ensuremath...
...hrm{cab}}}+\ensuremath{T_\ensuremath{\mathrm{rec}}} \right] },
\end{displaymath}](img6.png) |
(1) |
where
is the receiver image gain,
the telescope forward
efficiency,
the airmass,
the
atmospheric opacity in the signal band,
the mean physical
atmospheric temperature,
the ambient temperature in the receiver
cabine and
the noise equivalent temperature of the receiver and the
optics. All those parameters are easily measured, except
, which
depends on the amount of water vapor in the atmosphere and which is
estimated by complex atmospheric models.
The
value is expressed so that all these terms are corrected for
the attenuation by the atmosphere, the coupling of the antenna to the sky,
and the side-band rejection. In other words, the system temperature is
given in units that assume a perfect antenna (coupling equal to 1) located
outside the atmosphere for a single-sideband signal.
Next: Power and sensitivity measured
Up: The interferometric point source
Previous: The interferometric point source
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Gildas manager
2023-06-01