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Rayleigh and Mie Scattering

Rayleigh and Mie Scattering. Remote Sensing ERAU Dr. Darrel Smith September 30, 2008. Rayleigh & Mie Scattering. Rayleigh Scattering. Rayleigh Scattering. Light scattering off of air molecules (N 2 , O 2 ) Can be extended to scattering from particles up to ~ 1/10 .

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Rayleigh and Mie Scattering

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  1. Rayleigh and Mie Scattering Remote Sensing ERAU Dr. Darrel Smith September 30, 2008

  2. Rayleigh & Mie Scattering

  3. Rayleigh Scattering

  4. Rayleigh Scattering • Light scattering off of air molecules (N2, O2) • Can be extended to scattering from particles up to ~ 1/10 . • Rayleigh scattering off the molecules of the air givesrise to a “blue” sky. • Lord Rayleigh calculated the scattered intensity fromdipole scatterers much smaller than the wavelengthto be:

  5. Rayleigh Scattering

  6. Rayleigh Scattering from Particles When scattering from a particle of size d with light of wavelength , the Rayleigh scattering is found to be: where R is the distance to the particle, n is the index of refraction, and  is the scattering angle.

  7. Cross Section The cross-section of a particle is determined by the following equation where: is the differential cross section. Another way of representing this is by:

  8. Problem Find the Rayleigh scattering cross-section for scattering from a small particle of size d using a wavelength  if the scattered intensity is: where R is the distance to the particle, n is the index of refraction, and  is the scattering angle. Answer:

  9. Scattering from molecules A 5 mW green laser pointer isvisible at night due to Rayleighscattering and airborne dust.  = 532 nm

  10. Homework Problem #1 If the Rayleigh cross-section for an N2 molecule is 5.1 x 10-31 m2 at a wavelength of 532 nm (green light), what would be the characteristic size of an N2 molecule?Assume that the index of refraction of air is:nair = 1.000293

  11. Problem What is the number density nbeam for a 5 mW green laser pointer whose wavelength is 532 nm and whose cross-sectional beam size is 2 mm?

  12. Homework Problem #2 What fraction of the light from a 532 nm pen laser gets scattered every meter?

  13. Degree of Polarization • In general, Rayleigh scattering is for randomly polarized incident flux and the scattered flux will be polarized. • The degree of polarization induced by scattering from a small particle exposed to randomly polarized flux is: Bohren and Huffman (1998)

  14. Homework Problem #3 • Plot the “degree of polarization” as a function of scattering angle . • At what angle is the scattered light completely polarized? • How might you observe this?

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