This program is designed to test the effect of various options given in make_mwa_tied_array_beam on the calibration solution. The command line options for mwa_plot_calibration are a subset of those in make_mwa_tied_array_beam:
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usage: mwa_plot_calibration [OPTIONS] OPTIONS (RTS) -m, --metafits=FILE FILE is the metafits file for the target observation -c, --cal-metafits=FILE FILE is the metafits file pertaining to the calibration solution -C, --cal-location=PATH PATH is the directory (RTS) or the file (OFFRINGA) containing the calibration solution -N, --ncoarse_chans=NUM NUM is the number of coarse channels to include -R, --ref-ant=TILENAME Override the reference tile given in pq_phase_correction.txt for rotating the phases of the PP and QQ elements of the calibration solution. To turn off phase rotation altogether, set TILENAME=NONE. -U, --PQ-phase=PH,OFFS Override the phase correction given in pq_phase_correction.txt. PH is given in rad/Hz and OFFS given in rad, such that, the QQ element of the calibration Jones matrix for frequency F (in Hz) is multiplied by exp(PH*F + OFFS) Setting PH = OFFS = 0 is equivalent to not performing any phase correction -X, --cross-terms Retain the PQ and QP terms of the calibration solution [default: off] CALIBRATION OPTIONS (OFFRINGA) -- NOT YET SUPPORTED -O, --offringa The calibration solution is in the Offringa format instead of the default RTS format. In this case, the argument to -C should be the full path to the binary solution file. OTHER OPTIONS -h, --help Print this help and exit -V, --version Print version number and exit |
The three key options that this script is useful for testing are the -R, -U, and -X options. If none of these are provided, then the default behaviour is for the relevant values to be drawn from the file RUNTIME/pq_phase_correction.txt, where "RUNTIME" is the path set at VCSBeam compile-time. If there is an entry in pq_phase_correction.txt where the obsid falls between the "From" and "To" times (inclusive), then the values in the "Phase slope" and "Phase offset" columns are used for the -U option, and the value in the "Reference Tile Name" column is used for the -R option. For example, consider the following entry in pq_phase_correction.txt:
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# From_(gpstime) | To_(gpstime) | Phase_slope_(rad/Hz) | Phase_offset_(rad) | Referece Tile Name | Notes
1201478418 1280275218 7.7258e-09 0.4898 LBG8 # From https://wiki.mwatelescope.org/display/MP/Polarimetry (accessed: 19 Aug 2021) |
The command
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mwa_plot_calibration -m 1240826896_metafits_ppds.fits -c 1240827912.metafits -C /PATH/TO/RTS/OUTPUT -N 24 |
would be equivalent to
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mwa_plot_calibration -m 1240826896_metafits_ppds.fits -c 1240827912.metafits -C /PATH/TO/RTS/OUTPUT -N 24 -U 7.7258e-09,0.4898 -R LBG8 |
If there is no entry where the obsid of the target obs (in this case, 1240826896) falls between the From and To times, then the default behaviour is for the "dividing through by a reference antenna" (-R) step to be skipped, and for no extra phase slope (-U) to be applied. To force this behaviour (regardless of wheter there is a corresponding entry in pq_phase_correction.txt), the following command line options should be used:
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mwa_plot_calibration -m 1240826896_metafits_ppds.fits -c 1240827912.metafits -C /PATH/TO/RTS/OUTPUT -N 24 -U 0,0 -R NONE |
Output
The mwa_plot_calibration program outputs the calibration solution as ASCII text with a self-describing (#-commented) header, printed to stdout. To store this output in a file for later plotting, use standard redirection, example:
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mwa_plot_calibration -m 1240826896_metafits_ppds.fits -c 1240827912.metafits -C /PATH/TO/RTS/OUTPUT -N 24 -U 0,0 -R NONE > solution.txt |
The outputted file can than be used with plot_calibration.py to generate plots such as those shown below.
