2.2.1.0 calibrater.posangcal

2.2.1 Apply position angle calibration to an existing cal table
Description

This function is used to apply position angle calibration for observations made using circularly polarized feeds. According to the Measurement Equation formalism, this correction should be applied to a D (instrumental polarization) calibration table.

If no D calibration is performed (and thus no such table is available), the correction can be applied to a G table, but it should NEVER be applied to both, and always applied to a D table if one is available. An input table must be specified. If no output table is specified, then the input table will be modified in place.

Specify, as a vector of values, a position angle adjustment (in degrees) for each spectral window. If only one value is specified, it will be duplicated to all spectral windows; otherwise, the number of values specified must match the number of spectral windows. The sign convention for the position angle adjustment is such that the specified value is the that which, when added to the position angle implied by the data, will yield the correct position angle. For example, if G-, D-, and P-calibrated data for 3c286 suggests a position angle of 45 degrees, the posangcor value should be -12 degrees as this will yield the correct position angle of 33 degrees when added. In general, posangcor equals correct position angle minus observed position angle.

A future version of this function will have an option to recognize standard position angle calibrators and determine the correction automatically.

(NB: It may be desirable to use solutions for ’X’ to handle position angle calibration, rather than this method.)


Inputs
posangcor	Position angle corrections (degrees)
	allowed:	doubleArray
	Default:
tablein	Input calibration table name
	allowed:	string
	Default:
tableout	Output calibration table name. Default is input table name.
	allowed:	string
	Default:

This example takes an existing calibration table containing D Jones matrices, and applies a position angle calibration of 45 and 54 degrees to spectral windows 1 & 2, respectively, writing the result to a new table. The observed position angles for 3C286 must have been 45 and -21 degrees; the corrections specified yield the correct value of 33 degrees when added to the observed values.

calibrater.posangcal - Function