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9.6 Phase correction during off-line data reduction

In a typical data reduction session, the atmospheric phase correction hides behind two unobtrusive buttons (Fig.9.8). The default of the PHCOR button will calculate the phase correction on a scan basis, i.e. only the corrected amplitudes will be used and not the phases. There are two reasons to be cautious about the corrected phases:


  
Figure 9.7: Baseline based amplitudes, uncorrected phase and monitor corrected phase at 86.2 GHz for a cloudy data section. The clear sky model over-estimates the correction and would result in serious amplitude loss. The off-line data reduction software will identify those parts and disable the correction there.
\resizebox{16.0cm}{!}{\includegraphics[angle=270]{mb1f7.eps}}

The part of related header variables is accessible over
CLIC
> VARIABLES MONITOR
Some items are scan-based in time resolution, others can be expanded to a time scale of one second over the total power signal. One can plot the following quantities related to the phase correction:

In order to check the validity of the phase correction, the standard reduction runs the command
CLIC
> STORE CORRECTION AUTO 15
i.e. CLIC will test the phase calibrator observations (type P) if the application of the phase correction improves or degrades the amplitudes, and will declare the correction on source observations (type O) in a
$\pm15$ minutes time window for good.

Apart from AUTO, one can use GOOD and BAD for a manual override of the diagnostics, and SELF to check the amplitude for each scan (indifferent to type O or P) for strong sources.


  
Figure 9.8: The CLIC calibration package menu, with phase correction related items marked.
\resizebox{16.0cm}{!}{\includegraphics{mb1f8.eps}}


next up previous contents
Next: 9.7 Frequently asked questions Up: 9. Atmospheric Fluctuations Previous: 9.5 Current phase correction
S.Guilloteau
2000-01-19