2.2.1.0 calibrater.setsolvegainspline

calibrater.setsolvegainspline - Function

2.2.1 Specialization of setsolve for cubic spline G (time-dependent gain) solving
Description

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

The visibility data are averaged in frequency (for multi-channel data) prior to the solution. The spline timescale (time between knots) is specified in the splinetime paramter, which defaults to 10800 seconds (3 hours).

The solution is performed for phase and/or amplitude according to the mode parameter. For phase solutions only, use mode=’PHAS’. For amplitude solutions only, use mode=’AMP’. If both are desired, use mode=’PHASAMP’, and both will be solved for using the same spline timescale (this mode also assumes that all calibrators have the correct relative flux densities). If solving for phase and amplitude separately (usually in this order), be sure run setapply to specify application of the first one when solving for the second one. The combined solution will be stored in the table specified for the second solve. If it is desired that the first solution table be preserved, use a new table name.

Different spline timescales may be used for phase and amplitude. If multiple fields are present, they will be used together to obtain a single solution. In mode=’AMP’, it is important that the model flux densities of each fields be correct, so that a single, consistent gain function can be properly determined.

The parameters npointaver and phasewrap tune the phase-unwrapping algorithm when mode = ’PHAS’. Cycle slips are detected (and removed before the spline solve) when the median phase a sequence of length npointaver (in integrations) differs by more than phasewrap degrees from the previous sequence.

When solve is run, the solutions are obtained, and postscript plot of baseline data and solutions is generated and deposited in your working directory. Its name is the same as table, with .ps appended.

At this time, it is not yet possible to plot the antenna-based solutions themselves using plotcal.

After obtained, these solutions should be applied using type=’GSPLINE’ in setapply.

Pending improvements:

Generalize to dual polarization
Enable plots of antenna-based solutions (currently, only plots of baseline data and solutions are produced)

Arguments


Inputs
table	Output calibration table name
	allowed:	string
	Default:
append	Append to existing table?
	allowed:	bool
	Default:	false
mode	Phase or Amplitude mode?
	allowed:	string
	Default:	AMP PHASAMP PHAS
splinetime	Spline timescale (sec)
	allowed:	double
	Default:	10800
preavg	Pre-averaging interval (in sec)
	allowed:	double
	Default:	0.0
refant	Reference antenna. Default is none.
	allowed:	int
	Default:	-1
npointaver
	allowed:	int
	Default:	10
phasewrap
	allowed:	double
	Default:	250

Returns
bool

Example

c:=calibrater(’3C273XC1.MS’);
c.setsolvegainspline (table=’gcal’,mode=’PHAS’);
c.solve();

c.reset();
c.setsolvegainspline (table=’gcal’,mode=’AMP’);
c.solve();
c.done();

In this example, a spline solution is first found for phase, then for amplitude.

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