Array Calibration

We list here observing modes that are used, at time intervals, to calibrate the array itself. The results are useful to all projects.

Pointing calibration session A set of pointing calibrations on several pointing calibrators all across the sky. Needs to be done only after some antennas have been moved. Has to be checked periodically. Occasionally one should measure the relative pointing of the different frequency receivers, by using either a strong planet in total power mode or a strong quasar in interferometric mode.

Baseline calibration session Done by cross-correlation scans on several calibrators all across the sky. Needs to be done only after some antennas have been moved (but some antennas which have not been moved have to be included in the sub-array). One may observe for some time with antennas the positions of which have not been precisely measured, provided that these positions are known for the final reduction.

Delays calibration Needed for most interferometric observations. One observes a strong point source (calibrator), in the observable sky, for a very short time to measure the relative delays to the antennas.

Beam shape calibration Holography measurements on cosmic source, to monitor beam shape and focusing of antennas as a function of elevation.