RTP temperature measurement using conventional pyrometric technique has serious limitations such as uncertainty of emissivity, lamp interference, and window/chamber heating effect. In this paper, we propose to compensate for these effects using a real-time computational algorithm based on physical model of pyrometric detectors and wafer temperature dynamics. We consider an RTP system for processing 200 mm wafers with five circular zones of heating lamps and ten pyrometric sensors, five of which measure the radiation from five optically isolated dummy lamps and the rest measure the radiation of the wafer back side at different radial positions. Thermocouple measurements are also used to identify the model parameters. Part I of the paper is concerned with modeling and parameter identification.