Load calibration and determination of the zenith opacity

The hot and cold load as well as the atmosphere in a region devoid of signal are measured in turn. From Eq. 2, it is easy to show that

  $\displaystyle \frac{\ensuremath{T_\ensuremath{\mathrm{hot}}\ifthenelse{\equal{}...
...emath{C}_\ensuremath{\mathrm{hot}}-\ensuremath{C}_\ensuremath{\mathrm{cold}}},
$ (11)
where From this equation, we deduce \ensuremath{T_\ensuremath{\mathrm{sky}}\ifthenelse{\equal{tot}{}}{}{^\ensuremath{\mathrm{tot}}}}. Using an atmospheric model and Eqs. 79, the total opacity of the atmosphere at signal and image frequencies are then fitted.