2.1.1.0 calibrater.setapply

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calibrater.setapply - Function

2.1.1 Arrange to apply calibration

Description

This function is used to specify the calibration components which should be applied during subsequent execution of the solve and correct functions. This function should be executed as many times as necessary to specify all desired calibration components.

Each calibration component represents a separate calibration matrix correction included in the measurement equation. The different types correspond to different instrumental and atmospheric effects. Calibration components are available as calibration tables generated by previous solve executions (types ’B’,’BPOLY’,’G’,’GSPLINE’, ’D’,’DF’,’T’,’M’,’MF’,’X’), or are calculated analytically on the fly (types ’P’, ’TOPAC’, ’GAINCURVE’). Upon execution of solve or correct, the group of specified calibration components will be applied in the order prescribed by the Measurement Equation formalism.

The parameters are as follows:

type: The calibration type being specified. This is only required for analytic types (’P’,’TOPAC’,’GAINCURVE’). When specifying an existing pre-solved calibration table, it is not necessary to explicitly specify the type; this will be discerned from the table. (Specifying the type as well as the table will force a check that the table contains solutions of the specified type.
For type=’GAINCURVE’, an elevation-dependent correction will be applied using parameters read from the data repository. Currently, this is only supported for the VLA.
t: This parameter will be used in a future release to control the range of applicability of the specified calibration. Currently, it is ignored.
table: For pre-solved calibration, the file name of the table to apply.
field: The fields to select from the specified table, using MS Selection syntax (as in selectvis).
interp: The desired type of time-dependent interpolation. Use interp=’nearest’ to calibrate each datum with the calibration value nearest in time. Use interp=’linear’ to calibrate each datum with calibration phases and amplitudes linearly interpolated from neighboring (in time) values. In the case of phase, this mode will assume that phase jumps greater than 180 degrees between neighboring points indicate a cycle slip, and the interpolated value will follow this change in cycle accordingly (i.e., the implied rate will always be less than 180 degrees per sample). Use interp=’aipslin’ to emulate the basic interpolation mode used in classic AIPS, i.e., linearly interpolated amplitudes, with phases derived from linear interpolation of the complex calibration values. While this method avoids having to track cycle slips (which is unstable for solutions with very low SNR), it will yield a phase interpolation which becomes increasingly non-linear as the spanned phase difference increases. The non-linearity mimics the behavior of interp=’nearest’ as the spanned phase difference approaches 180 degrees (the phase of the interpolated complex calibration value initially changes very slowly, then rapidly jumps to the second value at the midpoint of the interval). If the uncalibrated phase is changing this rapidly, a ’nearest’ interpolation is not desirable. Usually, interp=’linear’ is the best choice. The interp parameter is applicable to any calibration type, as long as there are sufficient solutions available to perform the interpolation. Note that calibration solutions which have been determined for only one timestamp will default to ’nearest’. More interpolation options (e.g., ’cubic’) will be added in the future.
select: Used to specify general selection of a subset of calibration measurements from the table to be applied to the visibility data. Arbitrary cross-calibration is possible by combining this function with the setdata function. The string specified must be a valid TaQL expression.
spwmap: This parameter is used to indicate how solutions derived from different spectral windows should be applied to other spectral windows. Nominally, data in each spectral window will be corrected by solutions derived from the same spectral window. This is the default behavior of spwmap, i.e., if spwmap is not specified, calibrater will insist that data be corrected by solutions from the same spw. Otherwise, spwmap takes a vector of integers indicating which spectral window solutions to apply to which spectral window data, such that spwmap[j]=i causes solutions derived from the i-th spectral window to be used to correct the j-th spectral window. For example, if (say) bandpass solutions are available for spws 0 & 2, and it is desired that these be applied to spws 1 & 3 (as well as 0 & 2), respectively, use spwmap=[0,0,2,2]. Even if some spws do not require an explicit spwmap setting, yet one or more does, it is safest to specify it explicitly for all, e.g., spwmap=[0,1,3,3] indicates that spw 2 will be corrected with solutions from spw 3, and the others will behave nominally. Note that if no solutions exist for any of the spws specified in spwmap, an error message will result.
calwt: If set True, the data weights will be calibrated along with the data. This is usually desirable.
opacity: For type=’TOPAC’, an elevation-dependent opacity correction will be applied according to the zenith opacity value supplied in the opacity parameter. Currently, only one zenith opacity value can be supplied, and it is used for all antennas.

Use the state function to review the list of calibration components that have been set for application.

Pending improvements:

Enable variety of interpolation modes and timescales
Allow for antenna- and time-dependent opacities

Arguments


Inputs
type	Component type
	allowed:	string
	Default:	B BPOLY G GSPLINE D P T TOPAC GAINCURVE
t	Interpolation interval (seconds)
	allowed:	double
	Default:	0.0
table	Calibration table name
	allowed:	string
	Default:
field	Select on field
	allowed:	any
	Default:	variant
interp	Interpolation type (in time)
	allowed:	string
	Default:	aipslin nearest linear
select	TAQL selection string. Default is no selection.
	allowed:	string
	Default:
calwt	Calibrate weights?
	allowed:	bool
	Default:	false
spwmap	Spectral windows to apply
	allowed:	intArray
	Default:	-1
opacity	Array-wide zenith opacity per antenna (for type=’TOPAC’)
	allowed:	doubleArray
	Default:	0.0

Returns
bool

Example

cb.open(’ngc5921.ms’)
cb.selectvis(field=’N5921*’)
cb.setapply (type=’G’, table=’gcal’, field=’1445*’)
cb.setapply (type=’P’)
cb.correct();
cb.close();

In this example, we apply parallactic angle corrections and a gain
calibration derived from a field whose name matches ’1445*’ in a caltable
called ’gcal’ to data for a field matching ’N5921*’

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