Inscattered

Inscattered is a term used in optics, atmospheric science, and radiative transfer to describe light that has been scattered into the observer’s line of sight by a participating medium such as the Earth's atmosphere, fog, or seawater. It contrasts with out-scattered light, which is redirected away from the line of sight, and with unscattered direct transmission.

In radiative transfer, inscattered light is part of the source term that replenishes radiance in a given direction due to scattering from all other directions. The amount of inscattered radiance depends on the scattering properties of the medium, including the phase function which governs angular redistribution, the single-scattering albedo, and the optical depth along the light path. Multiple scattering leads to increasingly diffuse inscattered light.

In the atmosphere, inscattered skylight from the sun gives the blue color of the daytime sky and contributes to the appearance of the horizon at sunrise and sunset. In cloudy or dusty conditions, scattering by clouds or aerosols modifies the color and brightness by increasing inscattered contributions. In ocean optics, inscattered light shapes the color of water and the visibility range by redirecting photons back toward a viewer after interactions with particles and molecules.

Computationally, inscattered light is estimated in remote sensing and computer graphics via volume rendering, Monte Carlo radiative transfer, or discrete ordinates methods. Common modeling parameters include the phase function P(θ), the single-scattering albedo ω0, and the optical depth τ. The concept is fundamental to understanding radiance in turbid media and to interpreting measurements of sky and surface radiance.