Keywords: pdbi-atm-pha-corr

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## In the calibration program (CLIC):

- Filling in the data parameters of receiver 2: Receiver 1 (3mm) data recorded before Nov. 11 1995 did not contain information on receiver 2 parameters, on which the phase correction is based. The current CLIC version automatically fills in these parameters when the data is read. Of course this only works if at least one correlator unit was connected to receiver 2. An informational message is given when this operation is done. This has been effective for some time already (2 months).
- Solving the atmospheric calibrations for the atmospheric monitor parameters. For the newest data (since Nov 11, 1995) this is done in real time. For older data this must be done manually, using either command `ATMOSPHERE`, which does exactly what is currently done by RDI at Bure, or command `MONITOR`. To execute these commands, the currect index of CLIC should include all data to be processed, including the atmospheric calibrations scans (procedure `CALI`).
- Setting a reasonable value for . This is done using command `MONITOR` which applies the second option described above: a linear fit to . The description of the command is:

  `MONITOR delta_time`

  The scans in the current index are grouped in intervals of maximum duration `delta_time' (in seconds); source changes will also be used to separate intervals. In each interval a straight line is fitted in the variation of atmospheric emission as a function of time; this line will be the reference value for the atmospheric correction.

  The default for `delta_time' is 3600 s, which usually results in using the on-source time between two phase calibrator observations as intervals for evaluation of .

  One may also try and extend `delta_time' and use this command to process the source observations and the phase calibrator observations separately (but beware that using very long times will produce long term phase drifts into the phase correction, which will have to be removed by the usual phase calibrations anyway).

  After using this command, one may plot using `SET Y ATM_REF` and `SET X TIME`, in antenna mode; itself is available with `SET Y ATM_EM`.

- Finally, applying (or not) the correction is done via `SET PHASE ATMOSPHERE` (or `SET PHASE NOATMOSPHERE`). This should work for all plots and table construction, focus solving, flux solving, .... When the corrected spectral line data is available, it will switch to the phase-corrected average records.

  After a plot, one may check the coefficients used by typing `SHOW CORR`. The coefficients are given in radians per unit of .

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