Instrumental calibration

   

The instrumental calibration should:

• detect grossly malfunctioning antennas so that faults can be corrected while the observations are in progress, and
• monitor the amplitude and phase stability of the instrument rapidly enough that any changes can be corrected by interpolation throughout the run.

In a well-designed array, most instrumental fluctuations (apart from phase jumps) are slow, so that observations of an unresolved strong calibrator every few hours or more will monitor the instrument adequately. Bear in mind however that if the instrumental calibration detects a discontinuity such as a phase jump, you may have to discard all the data between consecutive calibration observations for the antenna-IF in which the jump occurred (unless the source being imaged is strong enough that the precise time of the jump can be located in the source data--in which case you can probably self-calibrate it anyway).

Calibrators for purely instrumental monitoring should be chosen primarily for their strength rather than for closeness to the target(s).