M.R.Rosa
STECF,ESA
This contribution revolves about computer models of astronomical instruments and their application in advanced calibration strategies and observation model based data analysis. The historical connection between calibration and data analysis is reviewed. The success of physical models in the analysis of observational data with strong instrumental signatures is shown, and a concept for model based calibration developped. A discussion of advantages for observatory operations, observing, pipeline processing and data interpretation is accompanied by a briefing about the current status of the Observation SImulation and Instrument Modeling project at the STECF and ESO.