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Plateau de Bure Online Calibration
Some of the mentioned terms are partially estimated on real time so
that the stored visibilities are already corrected from their
contribution. Specific OBS commands, a dedicated GILDAS software
package (RDI) and some CLIC procedures are used to
produce and reduce the following scans:
- CALI: Each scan consists of two or three subscans,
obtained by the OBS command CALIBRATE. They are used to
measure the atmospheric transmission and receiver temperature,
converting backend counts in antenna temperature outside atmosphere
(which is a factor in , excluding pointing and focus terms).
- IFPB: Two subscans are obtained by the OBS command
BANDPASS, which switches the correlator entries to a common noise
source. Thus all the and are measured, except
for a residual delay (visible as a constant phase slope with respect
to frequency) due to path differences between the noise source and
the antenna connections to the correlator.
- GAIN: This procedure allows measuring the sideband gain
ratio of the receivers, by looking at a strong cosmic source (in
practice, only is computed, although the phase term
could also be derived). Since this ratio only depends on the
receiver tuning, in particular on the backshort tuning, a CALIBRATE scan is made just after tuning modifications.
Results from CALI and IFPB observations are applied to the
data by the automatic data compression job. Corrections from tuning
modifications are introduced in OBS by the operator just after GAIN, at the beginning of the observations. Therefore, in principle,
amplitude errors should only be due to phase noise, pointing and focus
errors.
Next: Offline Calibration; the rules
Up: Appendix: Calibration Principles
Previous: Baseline versus Antenna based
Contents
Gildas manager
2024-03-28