Plateau de Bure Real-time Calibration

For the PdBI, some terms are (partially) estimated in almost real time, using specific OBS command (and the associated procedures in CLIC which can be used ass selection criterium): CALIBRATE (CALI), BANDPASS (IFPB), and GAIN (GAIN).

• CALI
  This procedure consists in two subscans obtained by OBS command CALIBRATE. It measures the atmospheric transmission and receiver gain, converting backend counts in antenna temperature outside atmosphere (a factor in AA_i, excluding pointing and focus terms).

• IFPB
  This procedure consists in two subscans obtained by OBS command BANDPASS, in which the correlator entries are switched to a common noise source. Thus all the AC_ijk and PC_ijk can be measured, except for a residual delay (visible as a constant phase slope as function of frequency) due to path differences between the noise source and the antenna connections to the correlator.

• GAIN
  This procedure measures the sideband gain ratio of the receivers, by looking at a strong cosmic source (in practice, only AI_i is computed, although the phase term PI_i could also be derived). Since this ratio only depends on the receiver tuning, and in particular on the backshort tuning, it need not be repeated frequently.

Results from CALI and IFPB observations are automatically applied to the data by the automatic data compression job. GAIN results are usually specified manually by the operator before proceeding with observations. After these two calibrations are applied, amplitude errors can only be due to phase noise, pointing and focus errors.