ska_sdp_instrumental_calibration.xarray_processors.rotation_measures module
Post-calibration fits.
- class ska_sdp_instrumental_calibration.xarray_processors.rotation_measures.ModelRotationData(gaintable, refant, oversample=5)[source]
Bases:
objectCreate Model Rotation Data
- Parameters:
- get_plot_params_for_station(stn=None)[source]
Getter for plot params for any particular station.
- Parameters:
stn (int) -- Station number.
- Returns:
- rm_vals: dask.array
rm value array.
- rm_spec: dask.array
rm spec array.
- rm_peak: dask.array
rm peak array.
- rm_est: dask.array
rm estimate array.
- rm_est_refant: dask.array
rm estimate of refant.
- J: dask.array
Jones array.
- lambda_sq: dask.array
lambda square array.
- xlim: dask.array
x-limit array.
- stn: int
Station number.
- ska_sdp_instrumental_calibration.xarray_processors.rotation_measures.model_rotations(gaintable, peak_threshold=0.5, refine_fit=True, refant=0, oversample=5)[source]
Fit a rotation measure for each station Jones matrix.
For each station, the approach discussed in appendix B of de Gasperin et al. (2019) A&A 622, A5, is used to estimate the angle of rotation in each Jones matrix as a function of frequency. The result is expressed as a spectrum of complex numbers and Fourier transformed with respect to wavelength squared. The peak of this RM spectrum is taken as the rotation measure for the station, and optionally improved upon using a secondary nonlinear fit to the original spectrum.
In the current form, each matrix is first multiplied by the Hermitian transpose of the matrix of a reference station at the same frequency, and the product is normalised by the L2 norm. This will likely be updated as actual data are processed.
- Parameters:
gaintable (
GainTable) -- Bandpass calibrated gainTable dataset to be to modelled.peak_threshold (
float, default:0.5) -- Height of peak in the RM spectrum required for a rotation detection.refine_fit (
bool, default:True) -- Whether or not to refine the RM spectrum peak locations with a nonlinear optimisation of the station RM values.refant (
int, default:0) -- Reference antennaoversample (
int, default:5) -- Oversampling value used in the rotation calculation. This determines the resolution of phasor. Note that setting this value to some higher integer may result in high memory usage.
- Return type:
- Returns:
A container whose rm_est attribute contains the estimated rotations. It also contains other data useful for plots.