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IMPLEMENTATION IN AIPS++

Figure 4 gives a schematic overview of how the formalism described here could be implemented in AIPS++. Obviously, the OO experts will determine what actually happens, but perhaps the following points are worth making:

• The Measurement Equation is enshrined in the Measurement Model (MM), which now described the actual instrument, including corrections. This is different from the Green Bank model, where the MM described an idealised instrument (and we did not know what to do about image-plane effects). I have no idea how the MM should be implemented, and whether it should contain the Correctors.

• The MM does not really have an inverse. All instrumental effects can be applied by corrupting the Sky Model (SM) and the uv-model, but generally not the other way around. Calibration consists of fiddling the parameters of the MM and the SM until the uv-model is equal to the measured uv-data. Any non-zero differences are inputs to a Generalised Solver (see below), which estimates improved values for instrumental and Sky Model parameters.

• We do not (yet) need a Source Model. The Sky Model projection will do for the moment.

• I would be interested in a clear idea about the precise relation between MM and Measurement Set (MS). Upon reflection, it does not seem such a good idea to put uv-data from different telescopes (or even observations) into a single MS. Separate MS's would make it easier to associate an MM with an MS. But of course it should be possible to include a collection of MS's into a calibration and/or imaging process.