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Дата изменения: Unknown Дата индексирования: Mon Apr 11 01:51:24 2016 Кодировка: Поисковые слова: m 11 |
To determine the bandpasses and the phase offsets, you need to use mfcal on an observation of a strong continuum source. Typically this would be 1253-055, 1921-293 or 0537-441. Typical inputs are as follows:
MFCAL | |
in=vela.fixed.uv | Input multi-source, dual-band dataset. |
select=source(1921-293) | Select the strong continuum ``bandpass'' calibrator. |
The important output of this step is a bandpass calibration table which will contain the relevant phase offsets. The output also contains antenna gain calibration tables, but this will be overwritten below.
In doing this step, you may well want to avoid using some edge channels in the bandpass calibration process. To achieve this, you can use the edge parameter of mfcal. The edge parameter sets the number of channels to drop for all bands equally. It does not allow you to set different number of channels to drop in the different bands. If the channels and bandwidth characteristics of the different bands differ significantly, the edge parameter probably does not give you sufficient flexibility. In this case, you could use uvflag to explicitly flag edge channels.
Note in this calibration scheme, it is implicitly assumed that the antenna gain changes are common to both frequency bands. This is a reasonable approximation given that the frequency separation between the bands is at most 2.7 GHz and potentially much less. Consequently the fractional frequency separation is at most a few percent, and so the calibration change between bands can be assumed to be minimal.
Typical inputs for mfcal follow. This assumes a continuum source as the phase calibrator and does a joint solution for the two polarisations:
MFCAL | |
vis=vela.fixed.uv | Input multi-source, dual-band dataset. |
select=source(1622-297) | Select phase calibrator. |
options=nopassol | Do not solve for bandpass. |
stokes=i | Do a joint solution for both polarisations. |
options=nopassol
.
This causes mfcal
to not attempt to solve for the
bandpass and phase offsets again, but rather to apply the previously
determined bandpass and phase offset solutions.
Typical inputs when using an SiO maser would be as follows: Typical inputs to mfcal are as follows:
MFCAL | |
vis=vela.fixed.uv | Input multi-source, dual-band dataset. |
select=source(oceti) | Select SiO secondary calibrator. |
options=nopassol | Do not solve for bandpass. |
stokes=i | Do a joint solution for both polarisations. |
line=chan,20,45 | Select the range of channels where the SiO |
signal is strong. |
At this point, you have a dataset that has been bandpass calibrated, and whose complex gains are determined as a function of time. All the remaining steps can be completed the same way as in the conventional approach: continue on from step 6 in Section 12.3.
Miriad manager