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Introduction

The calibration and imaging formalism used in AIPS++is based closely on the generic instrument model of Hamaker, Bregman and Sault (1996). This formalism, referred to as the Measurement Equation (ME), is instrument-independent and represents calibration effects in both the visibility and image plane as Jones matrices, with arbitrary parametrization and polarization basis. It's use in AIPS++is described by Cornwell (1995) and Noordam (1995), and references therein.

The calibration table format used in AIPS++was designed to support the fundamental principles on which the ME formalism is based. The definition of a standard calibration table format allows calibration components to be stored permanently for subsequent retrieval, application or modification. The current calibration table format revision level is v2.0.

The underlying principles on which the calibration table data format is based are described below.

• Data representation: AIPS++calibration tables are stored as AIPS++Tables, in keeping with the general rule in AIPS++ for all data visible to end users. As such, there is full user access to all data stored in a calibration table. These data can be retrieved, inspected and modified in the general user interface. The implementation of the calibration tables also uses other common Tables infrastructure such as TableMeasures.

• ME formalism: the calibration table format was chosen to support the key assumptions of the ME formalism, including support for: i) arbitrary polarization bases; ii) arbitrary Jones matrix parametrization; and, iii) generic, instrument-independent representation of calibration components.

• Unified calibration: the calibration table format has been designed to support both single-dish and synthesis calibration, antenna- and baseline-based Jones matrices, as well as visibility-plane and image-plane calibration components in a common format, with specialization where appropriate. This was chosen to maximize the re-use of calibration information and allow it to be transferred between different observing contexts.

• MS integration: the calibration table format is fully integrated with the MeasurementSet (MS) data format, supports all data representations possible in the MS, and re-uses all applicable column and keyword names for common underlying physical concepts. A calibration table can be attached to one or more MeasurementSets, but exists as a stand-alone table with a user-specified name. This supports both single-project and multi-project calibration schemes.

• History tracking: the calibration table format supports full tracking of the calibration history attached to each calibration solution or step in the calibration process.