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SKYDIP effects

Currently, $T_{amb}$ (the outside temperature) is used instead of $T_{cab}$ in Eq. 8. The effect of this assumption is intricate, because it is used also in the SKYDIP in which $F_{eff}$ and $Water$ are both determined. If the atmospheric opacities are low, the sky brightness $T_{sky}$ is a linear function of the number of airmass, and thus

T_{emi} = (1.-F_{eff})*T_{cab} + F_{eff} * C^{te} * Water * Air\_mass
\end{displaymath} (32)

In this case $F_{eff}$ is underestimated, because $T_{amb}$ is usually lower than $T_{cab}$. An increase in $Water$ will compensate the lower value of the forward efficiency. If the opacities are sufficiently high, the linearity is no longer preserved, and the fit will be bad. However, for 20 K difference between $T_{amb}$ and $T_{cab}$, the effect on $F_{eff}$ is only 0.01 for $F_{eff}$ around 0.90.

Gildas manager 2018-03-17