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Telescope Correction/Calibration Models

TelescopeModel is used to encapsulate all relevant information about the model of the components if the telescope, mainly thosed required for correction and calibration. A Telescope refers to two TelescopeModels: the default and the current. The former is used to contain initial information (e.g., as read from tape), and is ``read-only'' while the latter contains the model which is actually to be used, and which may be modified after initialisation using the default or some other model. TelescopeModels, are objects in their own right, and other models may be attached to a Telescope as desired, thus allowing, for example, TelescopeModels calculated during intermediate stages of processing to be preserved and reused.

TelescopeModel has services for correction of Yegs (CorrectYeg) and for updating and improving the TelescopeModel given measured and predicted YegSets (SolveFromYegs). Summarising, Yegs and TelescopeModels interact in a number of ways:

• Yegs, predicted Yegs (see ImagingModel below) and the TelescopeModel are used together to perform calibration solution and correction.

• Yegs contain things such as data values, u, v, w coordinates or pointing coordinates which are generally changed by the application of corrections.

• Correction/calibration solutions may be distributed among things like Receptor and Correlator - which are themselves part of TelescopeModel - using their solution services to perform updates.

Many TelescopeModels will contain parameters and functional forms which are clearly associated with the hardware components of a ``real'' telescope, together with other items which affect the measured Yeg. These might include antenna structure, RF and IF systems, the correlator and the atmosphere. The form of the TelescopeModel and its reference to the receptor or correlator objects for information will depend on the nature of the Telescope and the goals of the observations. The solution methods for updating the TelescopeModel will also vary enormously in complexity.

It is likely that all models would have additional services for printing and displaying parameters such as gains, or at least, for making these available to appropriate applications. It may also be useful to allow these parameters to be modified directly, and not simply by using the solver services.