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Obscurant representation is a key component of ground battlefield simulation, especially in the infrared domain. Obscurant are special counter measures (clouds) classically used to hide armored vehicles and deceive threatens. Obscurants are very difficult to represent especially because of multi diffusion effects of hot particles and smoke, but this representation is very important to quantify the efficiency of the decoy. This article describes a new model being involved in the simulation workshop CHORALE of the French MoD. The simulation workshop CHORALE developed in collaboration with OKTAL SE company is used by government services and industrial companies for weapon system validation and qualification trials in the infrared domain. The main operational reference for CHORALE is the assessment of the infrared guidance system of the Storm Shadow missile French version, called Scalp. This new model, integrated in CHORALE, enables to simulate the emitted radiance and the transmission of any pre computed obscurant cloud in the virtual battlefield. In the modeling step, the cloud is defined by a set of "voxels" (elementary volume elements). Each voxel contains the spectral extinction coefficient and the spectral scattering coefficients. The shape, i.e. the voxels content, is changing with time to convey the dynamic evolution of the obscurant. In the Non Real Time rendering step, primary rays are traced inside the clouds. For each voxel, scattering rays are then traced to their neighboring voxels and the local hot sources. Actually, ray tracing is used to solve the Radiative Transfer Equation. The main advantage is to be able to solve it taking into account the synthetic environment: the local terrain, the target hidden in the cloud, the atmospheric and weather conditions. The main originality is the multithreading ray tracing which enables to tackle huge quantities of rays in complex geometric environment.
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