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. , 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

$\ensuremath{T_\ensuremath{\mathrm{hot}}\ifthenelse{\equal{}{}}{}{^\ensuremath{\mathrm{}}}}$ and $\ensuremath{T_\ensuremath{\mathrm{cold}}\ifthenelse{\equal{}{}}{}{^\ensuremath{\mathrm{}}}}$ are the Rayleigh-Jeans temperature of the loads;
$\ensuremath{C}_\ensuremath{\mathrm{hot}}$ and $\ensuremath{C}_\ensuremath{\mathrm{cold}}$ are the associated measured counts.

From this equation, we deduce $\ensuremath{T_\ensuremath{\mathrm{sky}}\ifthenelse{\equal{tot}{}}{}{^\ensuremath{\mathrm{tot}}}}$ . Using an atmospheric model and Eqs.

–

, the total opacity of the atmosphere at signal and image frequencies are then fitted.