Physically Based Real-Time Rendering of Atmospheres using Mie Theory

Most real-time rendering models for atmospheric effects have been designed and optimized for Earth's atmosphere. Some authors have proposed approaches for rendering other atmospheres, but these methods still use approximations that are only valid on Earth. For instance, the iconic blue glow of Martian sunsets can not be represented properly as the complex interference effects of light scattered at dust particles can not be captured by these approximations. In this paper, we present an approach for generalizing an existing model to make it capable of rendering extraterrestrial atmospheres. This is done by replacing the approximations with a physical model based on Mie Theory. We use the particle-size distribution, the particle-density distribution as well as the wavelength-dependent refractive index of atmospheric particles as input. To demonstrate the feasibility of this idea, we extend the model by Bruneton et al. [BN08] and implement it into CosmoScout VR, an open-source visualization of our Solar System. In a first step, we use Mie Theory to precompute the scattering behaviour of a particle mixture. Then, multi-scattering is simulated, and finally the precomputation results are used for real-time rendering. We demonstrate that this not only improves the visualization of the Martian atmosphere, but also creates more realistic results for our own atmosphere.