The Scene Generator Module is in charge of simulating the observed scene, the energy arriving to the instrument detector elements. The simulation chain of the Scene Generator Module starts from the geo/bio-physical variable that is the target of the mission (the soil moisture, the salinity of the oceans, the chlorophyll, etc.). The electromagnetic radiation has a different response depending on the terrain properties and the environment (atmosphere, clouds, etc.). To model this response a Radiative Transfer Model (RTM) is applied to the input geo/bio-physical map. The RTM calculates either the reflectance (the reflected energy at Top-Of-Canopy, the TOC image), or directly the Top-of-Atmosphere image (TOA), which includes the propagation of the electromagnetic radiation through the atmosphere. Clouds also have an impact on the propagation of the energy.
The simulation flow of the Scene Generator Module is shown in the diagram below: