Use Case:
ObserveSingleField
Describe the actual observing actions needed to obtain data in the single
field interferometric mode.
Role(s)/Actor(s)
Primary: The AOS
Secondary:
Priority:
Major
Performance:
real-time; overhead should be minimal and dominated by hardware.
Frequency:
this mode is likely to be the most frequently used.
Preconditions:
all the user parameters have been properly entered and checked (UC SetupSingleField.html)
Basic
Course:
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The preamble block is executed (only once in the session).
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Doppler effect is calculated for the target source and current time.
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The receivers are set up and tuned.
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The correlator is setup.
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The pipeline is started.
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The bandpass calibration is executed, after automatic selection if so specified.
This includes observing this source at both the target frequency and the
calibration frequency.
-
The phase calibrator is selected if necessary by observing a few candidates
in the source vicinity, according to the selection policy as specified.
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If the phase calibrator is not suitable (too weak) as a pointing reference,
a pointing calibrator is selected.
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For each scheduled SB:
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Measure pointing and focus offsets on the pointing calibrator using the
standard procedures.
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Update the pointing and focus corrections using feed back from the pipeline.
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Record correlator output on the phase calibrator at the calibration frequency
then at the observing frequency (TBD) for a specified or calculated time.
-
Record correlator output on the target source at the observing frequency
for a specified or calculated time. This calculation is based on the current
phase rms or phase structure function (TBD).
-
Repeat steps 3 and 4 until the SB time is exhausted or the goals are achieved
(e.g. minimum rms reached).
Exception Course: If the phase rms increases over a specified limit,
the SB is terminated (keep the data observed so far, with appropriate flag).
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The system executes the associated postamble SB: the phase calibrator is
reobserved one last time.
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Optionally (if specified by the astronomer or if automatically determined)
the pipeline is instructed to make the final image and is closed.
Postconditions:
-
...
-
...
Issues to be Determined
or Resolved:
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An amplitude calibrator may need to be observed at some rate if the phase
calibrator is not strong enough.
-
That calibrator may also be used to monitor the relative phases at the
observing and the calibration frequency
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The policy to choose the bandpass calibrator is to be defined.
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The algorithm to determine the dwell time for phase calibration is TBD.
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Measuring the sideband gain ratios could be needed in the preamble if both
sidebands can be measured.
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This use case might be extended to deal with more than one target source.
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This use case might be extended to include a calibrator as a test source
at regular intervals, for quality evaluation.
Notes:...
Last modified: 2000/07/28 R. Lucas, 2000/11/10 D. Muders