2.2.1.0 calibrater.setsolvebandpoly

2.2.1 Specialization of setsolve for polynomial B (bandpass) solving
Description

This function is a specialization of the setsolve method which should be used to arrange for bandpass solving when polynomial solutions for B are desired, e.g., when SNR on calibrators is very low. Currently, this solving mode is available only for single polarization data.

Prior to the solution, the visibility data are averaged in time, and if multiple spectral windows are present (after running setdata), they are concatenated in frequency and one polynomial solution is delivered.

The solution is performed for both phase and amplitude, to the polynomial degrees specified in degamp and degphase (they can be different), and the result will be stored in the same table. The frequency domain of the solutions is limited to only the range of frequencies selected in setdata. When correcting data with these solutions (for other solves or with correct), only data within this domain will be corrected. Data outside (e.g., edge channels avoided in setdata for the solve), will not be corrected. Therefore, the same (or narrower) channel selection is recommended for all operations using solutions produced by this function and solve().

Like other solve types, the solve() function actually performs the solve according to the parameters set in this function, and for this type, it generates a plot file which shows the baseline spectra delivered to the solver (i.e., corrected according to any setapply() invocations, and time-averaged), with the derived solution (products of antenna-based bandpass polynomials) overlaid.

After solving, these solutions should be applied using type=’BPOLY’ in setapply.

The visnorm parameter is used to normalize the assembled spectral data, in a per baseline manner. If visnorm=T is used, this will have the effect of removing any non-frequency-dependent closure errors (e.g., as caused by source structure, or introduced by the instrument) from the data, and should be used with caution. The resulting solutions will be effectively normalized as well. When visnorm=F is used, closure errors in the data (as supplied to the solver) may be visible in the form of offsets between the data and solutions. For bandpass calibration, this is usually ok, as the shape of the bandpass is the most important aspect of the solution.

The bpnorm parameter controls normalization of the resulting solutions after the solve. Note that the baseline spectra plot does not show normalized solutions, even if bpnorm=T (the plot shows the data as provided to the core solver, and is generated before the solutions are normalized).

Note that use of bpnorm=T or visnorm=T will remove or prevent the storage of scaling information in the bandpass solutions. Sometimes it is desirable to store absolute scaling information in the bandpass solution; in these cases, bpnorm and visnorm must both be F.

The maskcenter and maskedge parameters control how many channels are ignored on-the-fly, at the center and edges of each input spectral window, respectively. To avoid edge channels, it is almost always better to flag these channels directly, or select against them in setdata. Aggressive use of maskedge (large values), will yield polynomial solutions which will tend to diverge at the edges (especially when the polynomial degree is also high), because maskedge does not change the frequency domain of the solutions. Such solutions should be used with caution in subsequent operations. (It is best to avoid use of maskedge.)


Inputs
table	Output calibration table name
	allowed:	string
	Default:
append	Append to existing table?
	allowed:	bool
	Default:	false
degamp	Polynomial degree for amplitude solution
	allowed:	int
	Default:	3
degphase	Polynomial degree for phase solution
	allowed:	int
	Default:	3
visnorm	Normalize data prior to solution
	allowed:	bool
	Default:	false
bpnorm	Normalize result?
	allowed:	bool
	Default:	true
maskcenter	Number of channels to avoid in center of each band
	allowed:	int
	Default:	0
maskedge	Fraction of channels to avoid at each band edge (in %)
	allowed:	double
	Default:	5.0
refant	Reference antenna
	allowed:	int
	Default:	-1

In this example, amplitude (degree 5) and phase (degree 7) Chebychev polynomial bandpasses are determined using the default parameters.

calibrater.setsolvebandpoly - Function