Physically Based Rendering of Rainbows under Various Atmospheric Conditions

Atmospheric phenomena such as rainbows and halos are caused by interference, diffraction and dispersion of light. To render the kinds of atmospheric phenomena, the spectrum of light should be taken into account because the optical phenomena greatly depend on the wavelength. Traditionally, rainbows are rendered by means of geometric optics. These methods, however, cannot render supernumerary rainbows and visual variations of rainbows depending on the radius of raindrops. The paper proposes a method for rendering rainbows taking into account wave optics and spectral distribution of light based on physical laws. The method is taking into account the distribution of raindrops, such as the radius and the density of raindrops in the atmosphere. And also we are taking into account atmospheric light scattering by air molecules and aerosol. These efforts enable our method to render the visual variations of rainbows and supernumerary rainbows. It helps visual understanding of rainbows and atmospheric conditions in meteorology.