Getting Started

Documentation

Glish

Learn More

Programming

Contact Us

Version 1.9 Build 1556

News	FAQ
Search	Home

calibrater.fluxscale - Function

	Package	synthesis
	Module	calibrater
	Tool	calibrater

Bootstrap the flux density scale from standard calibrators

Synopsis
fluxscale(tablein, tableout, reference, transfer, append, refspwmap, fluxd)

Arguments

tablein	in	Input calibration table name
		Allowed:	String
tableout	in	Output calibration table name. Default is tablein.
		Allowed:	String
		Default:	''
reference	in	Reference calibrator field names or indices
		Allowed:	Vector of strings
transfer	in	Transfer source field names or indices. Default is all other fields
		Allowed:	Vector of strings
		Default:	-1
append	in	Append to existing table?
		Allowed:	Bool
		Default:	F
refspwmap	in	List of alternate spw for referencing
		Allowed:	Vector of Ints
		Default:	-1
fluxd	out	Array of output flux densities
		Allowed:	Double
		Default:	[]

Returns
Bool

Description

This function is used to bootstrap the amplitude scale the calibration solutions according to specified reference calibrator(s) of known flux density. This is necessary when the flux densities of some of your calibrators were unknown (and thus were assumed to be 1 Jy) during G solving.

The bootstrapping is achieved by comparing the mean gain norm of the calibration solutions derived for the calibrators specified in reference (one or more sources with known flux densities at the time of G solving) with that of the calibrators specified in transfer, and enforcing the assumption that the antenna gains are constant, on average. The gain solutions for the transfer sources are then re-scaled accordingly.

If no transfer fields are specified, then the solutions for all non-reference fields in tablein will be re-scaled.

If no tableout is specified the input table will be overwritten with the scaled solutions. Note that the resulting table will only contain solutions for those fields implicit in the reference and transfer specifications. Use append=T to append the scaled solutions to an existing table.

Use the refspwmap parameter to indicate how data for different spectral windows should be matched in calculating the flux density scale factor for transfer fields. The default behavior for refspwmap is to insist on precisely matching spectral windows for reference and transfer fields. When specified, the refspwmap parameter takes a vector of integers indicating which spectral window solutions to use as the reference for others, such that refspwmap[j]=i causes solutions (from reference fields) observed in the i-th spectral window to be used to reference solutions (from transfer fields) observed in the j-th spectral window. For example, for the case of a total of 4 spectral windows: if the reference fields were observed only in spw=2 & 4, and the transfer fields were observed variously in all 4 spws, specify refspwmap=[2,2,4,4]. This will ensure that transfer fields observed in spws 1,2,3,4 will be referenced to reference field data from spws 2,2,4,4, respectively. Note that if the transfer fields were observed only in spws 1 & 3, the same specification would work, but refspwmap=[2,2,4] would suffice. In this case, nothing need be specified for the 4th spw (there are no transfer fields there), and specifying 2 for the 2nd spw is actually inconsequential (though required so that the specification of 4 for spw 3 is properly interpretted).

The derived flux densities for the transfer fields will be reported in the logger, and returned to the glish variable specified in fluxd. This will be an 2D array of shape [number-of-spectral-windows X number-of-fields].

Note that elevation-dependent gain effects may render the basic assumption used here invalid, and so should be corrected for prior to solving for G, using types 'TOPAC' or 'GAINCURVE' in setapply.

Note that the visibility data itself is not used directly by this function.

Pending improvements:

• Allow antenna and uv-distance selection to improve results for resolved calibrators
• Set the visibility model according to the flux density results
• An option to use the data to derive the relative flux densities

Example

c:=calibrater('3C273XC1.MS');
c.fluxscale (tablein='3C273.gcal', tableout='3C273.gcal2', 
              reference='1328+307', transfer="0957+561 0917+624");
c.done();

This example takes an existing calibration table containing G solutions, and writes a scaled output version, using 3C286 (1328+307) as the reference calibrator, to derive properly scaled amplitude calibration for the transfer sources, 0957+561 and 0917+624.