This tool visualizes Monte Carlo photon transport through a cloudy atmosphere in a simplified 2D setting. The cloud field is a single vertical slice through a synthetic cloud, and the photons are shown in red.

Forward mode traces photons from above downward. The visible path enters the top of the domain as a collimated beam. At each scattering event, the direction changes according to either a Henyey-Greenstein phase function or an empirical Mie phase function in cloud. The distance between interaction events follows the exponential free-path law.

Backward mode traces rays from a camera upward and evaluates the sun contribution at each scattering event with a shadow ray. The strip below the main panel accumulates those camera samples progressively, gradually building up an image.

Ray march mode steps through the volume at fixed intervals, computing attenuation and point illumination at each step along a camera ray inside the chosen field of view. This approximation is cheap enough to enable real-time rendering, for example in video games, but is not as accurate as the full Monte-Carlo method shown in Backward Mode.

Extinction is computed as σ_ext = 1.5 · QC · ρ_air / (ρ_water · r_eff), with r_eff = 10 μm.