Light Scattering Rayleigh Scattering Mie Scattering What is

Light Scattering Rayleigh Scattering & Mie Scattering

What is Scattering? • Process by which particles suspended in a medium of a different index of refraction diffuse a portion of the incident radiation in all directions • No energy transformation results, only a change in the spatial distribution of the radiation • Function of ratio of particle diameter to wavelength of incident radiation

Scattering Plane • Defined by the two rays involved, the source-particle ray and the particle-observer ray • Determined by observation, not fixed in space. For example, if the observer moves, the scattering plane will move with the observer.

Rayleigh Scattering • Particles much smaller than wavelength of radiation • Proportional to 1/ λ 4 • Shorter wavelengths scattered much more than longer wavelengths • Air molecules (N 2 and O 2) just the right size to very effectively scatter the shorter wavelengths (blue light) of incident solar radiation => blue sky

Mie Scattering • Scattering by a isotropic, homogeneous sphere • Particle dimension comparable to wavelength of radiation (aerosols, water vapour) • Longer wavelengths scattered more than shorter wavelengths • More forward scattering • Scattering properties depend on wavelength, size, real and imaginary parts of refractive index, and size distribution

Angle-Dependent Phase Function

Phase Function Moments

Discrete Ordinate Radiative Transfer Code: DISORT

Theory • Fundamental Equation of RT • Phase Function Expansion • Can use addition theorem for spherical harmonics to expand P in Fourier cosine series over azimuthal angle

Theory (Contd…) • Expand I in Fourier cosine series • RT equation transformed into 2 M independent integro-differential equations • Integration performed by Gaussian quadrature (2 N ‘streams’) • Reference: http: //www. gps. caltech. edu/~vijay/Papers/RT_Models/DISORT%20 Report. pdf