Calibrating ALMA


In this talk I'll address specific calibration issues for ALMA, including the types
of calibration needed, as well as the (dynamical) selection of calibration sources.

As ALMA is an interferometer, the proper calibration of phases is essential, ranging
from calibration of the delay lines to taking into account atmospheric fluctuations,
mostly in the amount of water vapour in the troposphere. I'll discuss how ALMA achieves
this in practice, separating calibration for short- and long-term effects.

During operations, ALMA uses a database of calibrators from which the required ones
are selected during the observation: these dynamical calibrators (instead of fixed ones)
should be the best possible at the time of observation. The database query algorithm
employed will be briefly discussed as well.