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Background information

To perform synthesis processing, AIPS++ uses a formalism called the MeasurementEquation developed by Johan Hamaker, Jaap Bregman and Bob Sault. Details of the design and implementation of the software are available in the AIPS++ Notes series. See particularly the note by Cornwell and Wieringa (1996).

The MeasurementEquation describes the relationship between the unknown (polarized) Sky Brightness and the observed visibilities (or coherences). Calibration terms such as antenna gains and polarization leakage terms can be included, thereby allowing processing of synthesis data using a potentially complicated model for the measurement process. At the time of writing, the form of the ME used is as follows:

2-dimensional Fourier transforms to and from the Sky plane,
Antenna-based feed angle correction: the P-terms (these include both parallactic angle rotation for alt-az mounts such as the VLA and feed angle offsets for equatorial mounts such as the WSRT)
Antenna-based atmospheric gain errors: the T-terms,
Antenna-based, electrical-path-dependent complex gain errors: the G-terms,
Antenna-based bandpasses: the B-terms
Antenna-based complex polarization leakage terms: the D-terms,
Correlator-based complex gains: the M-terms

AIPS++ synthesis data is stored in a MeasurementSet, which is an AIPS++ Table obeying certain conventions as to columns and subtables that must be present. See the note by Wieringa (1996) for an exact specification of the contents of the MS.

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