Monitor

The first atmospheric phase correction scheme was based on the total power measured in the 1mm band (when dual-frequency observing was available). The calibration scans are processed similarly to the regular astronomical calibration (see section 4.8.1), then the derivative of the path length over the emission temperature of the atmosphere at the atmospheric monitoring frequency is computed.

It is possible to fit a straight line within a time $\delta t$ to remove drift of non-atmospheric origin (such as receiver gain variations), before computing the corrections.

As for the WVR, this correction was applied online and can only be recomputed for the continuum units.