Atmosphere

Participating Media

大气粒子的种类

• Volume filled with particles
• Interact differently with light depending on its composition

大气层有两种粒子构成:
(1) 各种气体分子
(2) 气溶胶
这些是光的介质，是产生各种光学现象的原因。

气体分子直径远小于光的波长，气溶胶的直径与光的波长相似，因此表现出完全不同的视觉效果，也对应两种不同的模型。

How Light Interacts with Participating Media Particles?

(1) 吸收 (2) 散射 (3) 自发光

Volume Rendering Equation (VRE)

(1) 通透度 (2) 有多能量向视线方向辐射

气体分子散射模型 - Rayleigh Scattering

Scattering of light by particles that have a diameter much smaller than the wavelength of the radiation (eg. air molecules)

Rayleigh，用于气体分子。特点：

1. 均匀散射
2. 波长越短(紫)，散射越多
3. Certain directions receive more light than others front-back symmetry

• Shorter wavelengths (eg. blue) are scattered more strongly than longer wavelengths (eg. red)

Rayleigh Scattering Equation

\(\lambda\)：波长。\(\theta\)：夹用。\(h\)：海拔高度。

Why Sky is Blue

气溶胶散射模型 - Mie scattering

Scattering of light by particles that have a diameter similar to or larger than the wavelength of the incident light (eg. aerosols)

Mie，用于气溶胶。特点：

1. 有方向性，沿着光的方向会强一点
2. 对波长不敏感。

Mie Scattering Equation

• g > 0, scatters more forward Mie scattering
• g < 0, scatters more backward
• g = 0, Rayleigh scattering

Mie Scattering in Daily Life

• Exhibit a strong forward directivity (halo effects around sun)
• Scatter light of all wavelength nearly equally (fog effects)

\(O_3\) 和 \(CH_4\) 吸收短波，使物体表现出蓝色。
假设空气中 \(O_3\) 和 \(CH_4\) 是均匀分布的。

本文出自CaterpillarStudyGroup，转载请注明出处。
https://caterpillarstudygroup.github.io/GAMES101_mdbook/