Continuum Calibration

The description above assumes that the source signal comes only from the (so-called) signal sideband. This is of course not true for continuum radiation. If we neglect spectral index effects, one can derive the proper calibration of a continuum source from the description above. Tcal should be multiplied by

$$\frac{1}{1 + Gain\_i * e^{(Tau\_s - Tau\_i) * Air\_mass}}$$ (15)

Similarly for spectral line observations, if you are interested in the image band, Tcal should be multiplied by

$$e^{ (Tau\_i - Tau\_s) * Air\_mass} / Gain\_i$$ (16)