The SE-Workbench technology is used to perform multi-sensors simulations on complex 3D synthetic environment. The SE-Workbench enables the user to create virtual and realistic multi spectral 3D scenes, and generate the physical signal received by a sensor, typically infrared (IR), radar (EM) and acoustic (AC) sensors. To evaluate the efficiency of visible and infrared sensors, simulation tools that give a good representation of physical phenomena, are used. This article describes the elements used to prepare data (3D database, materials, atmosphere, ...) for the simulation, and the set of tools (SE-FAST-IR), used in the SE-Workbench-IR for the Real Time simulation in the infrared spectrum. The SE-AGETIM tool turns geographical source data (including GIS facilities) into meshed geometry enhanced with the sensor physical extensions, fitted to the ray tracing rendering of the SE-Workbench and to the Real Time rendering capabilities of the SE-Workbench in infrared. The SE-FAST-IR package allows the compilation and visualization of 3D databases for infrared simulations. It enables one to visualize complex and large synthetic scenes for a wide set of real and pseudo-real time applications. The SE-FAST-IR software automatically computes radiance textures, Open GL light source and fog-law parameters for predefined thermal and atmospheric conditions specified by the user. It is based on the physical model used by the ray-tracing tool of the SE-Workbench, which enables the development of a coherent and powerful validation method.