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calibrater.setapply - Function

	Package	synthesis
	Module	calibrater
	Tool	calibrater

Arrange to apply calibration

Synopsis
setapply(type, t, table, interp, select, spwmap, unset, opacity, rawspw)

Arguments

type	in	Component type
		Allowed:	String from 'B','BPOLY','G','GSPLINE','D','P','T','TOPAC','GAINCURVE','M','MF','K'
t	in	Interpolation interval (seconds)
		Allowed:	Float
		Default:	0.0
table	in	Calibration table name
		Allowed:	String
		Default:	' '
interp	in	Interpolation type (in time)
		Allowed:	String from 'nearest', 'linear', 'aipslin'
		Default:	'nearest'
select	in	TAQL selection string. Default is no selection
		Allowed:	String
		Default:	' '
spwmap	in	Spectral windows to apply
		Allowed:	Vector of Int
		Default:	-1
unset	in	If T, unset apply of this type
		Allowed:	Bool
		Default:	F
opacity	in	Array-wide zenith opacity (for type='TOPAC')
		Allowed:	Float
		Default:	0.0
rawspw	in	Spectral window with data phases for application
		Allowed:	Float
		Default:	-1

Returns
Bool

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 will 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','T','M','MF','K'), or are calculated analytically on the fly (types 'P', 'TOPAC', 'GAINCURVE'). See the setsolve section for more information about the solvable types.

Use the interp parameter to specify 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. Use interp='aipslin' to emulate the basic interpolation mode used in classic AIPS, i.e., linearly interpolated amplitudes, with phases derived from 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 near future.

Currently, the interpolation interval is forced to t=0 for solved-for components, which means that the interpolation (or extrapolation) will extend indefinitely, as circumstances dictate. A future version of calibrater will use this parameter to limit the range in time over which interpolation/extrapolation will be permitted.

The interpolation type and timescale are, by definition, irrelevant for analytically calculated calibration types (e.g., the parallactic angle, P).

For solved-for components, the filename specified in table parameter must contain a calibration table of the type specified in type.

Use the select parameter to specify 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.

The spwmap 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 1 & 3, and it is desired that these be applied to spws 2 & 4 (as well as 1 & 3), respectively, use spwmap=[1,1,3,3]. 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=[1,2,4,4] indicates that spw 3 will be corrected with solutions from spw 4, 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.

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.

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.

Use the rawspw parameter to specify a spectral window from which the phase will be copied for application (in a baseline-based manner) to the data selected in setdata. The phases will be scaled by the appropriate frequency ratio. Note that this option currently only works when solving for or applying type='GSPLINE' solutions.

Currently, only single-polarization data will work with type='BPOLY' or type='GSPLINE'.

Use the state function to review the list of calibration components that have been set for application. To deselect a single component, run setapply with unset=T and type accordingly. Use the reset function to delect all components.

Pending improvements:

• Enable variety of interpolation modes and timescales
• Allow for antenna- and time-dependent opacities
• Generalize BPOLY and GSPLINE to dual polarization
• Provide more user-friendly selection

Example

c:=calibrater('3C273XC1.MS');
c.setdata();
c.setapply (type='G', table='gcal2', select='FIELD_NAME==FIELD1')
c.setapply (type='P' t=10.0)     
c.correct();
c.close();

In this example, 'G' solutions from FIELD1 in table gcal2, and 'P' solutions calculated on a 10-second timescale are applied to the entire visibility dataset.