How the data look like

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How the data look like

Let us assume that we are already looking at the data, in CLIC. After typing in CLIC find and later list we will see, e.g.:

    60 7684 QA12 3C454.3      P CORR CO10     6Cq-N17      12-NOV-2007 21:58  2.9
    61 7685 QA12 3C454.3      P CORR CO10     6Cq-N17      12-NOV-2007 21:59  2.9
    62 7686 QA12 3C454.3      P CORR CO10     6Cq-N17      12-NOV-2007 22:00  2.9

where each line corresponds to an observation subscan5. Each subscan contains the following information:

     - First column: Observation number
     - Second column: Scan number
     - Third column: Project name
     - Fourth column: Source name
     - Fifth column: Type of source (O=object, P=phase calibrator)
     - Sixth column: Type of scan procedure
     - Seventh column: Line name
     - Eighth column: Array configuration, i.e. antenna positions
     - Nineth column: Date
     - Tenth column: UT time
     - Eleventh column: Hour angle

The usual observational procedures (column sixth) and characteristics are:

     CORR: cross-correlation; 1 subscan (ss) is obtained per scan
     GAIN: cross-correlation to measure the sideband rejection; 1 ss
     FOCU: focus measurements in all the antennas; 5 ss
     POIN: interferometric pointing in all the antennas; 2 ss
     FLUX: cross-correlation to measure the flux; 1 ss
     IFPB: IF passband calibration, by observing a noise diode; 2 ss
     AUTO: autocorrelation; 1 ss
     CALI: atmospheric calibration, autocorr. on SKY, HOT [COLD] load; 2 [3] ss
     SKYD: sequence of autocorrelations to calibrate the 22 GHz receivers; 12 ss

By using the mentioned procedures, a typical sequence of observations is:

     - Receiver tuning followed by a sideband gain measurement
     - Radio frequency passband calibration on a bright source
     - Acquisitions on at least a flux calibrator, MWC 349 if possible
     - Check the pointing and focus on the predefined phase calibrator(s)
     - Possibly a flux measurement on this calibrator(s)
     - Cross-correlations on the phase calibrator(s)
     - Cross-correlations on source

About 3 minutes are spent on each phase calibrator, some more time if pointing and focus are performed, every 23 minutes on source. Pointing and focus are normally repeated every two transitions of 23 minutes on source. IFPB, AUTO and CALI scans are obtained before correlations to calibrate the observations in real time (see Sect. ).