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B Light propagation in water -- Is the scattering Rayleigh scattering?

  1. Oct 3, 2018 #1
    When light enters an ocean, the photons scatter elastic with water molecules yet the presence of opaque particles causes the depth to be limited.
    Is this scattering Rayleigh scattering? (like the scattering in our atmosphere)
    https://en.wikipedia.org/wiki/Rayleigh_scattering
     
  2. jcsd
  3. Oct 4, 2018 #2

    Lord Jestocost

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    The Rayleigh theory is not applicable to liquids, but one can refer to the Einstein—Smoluchowski theory.

    "In the Einstein—Smoluchowski theory, scattering is considered to be caused by the random motion of molecules which in a sufficiently small volume causes fluctuations of density and, therefore, of the dielectric constant."

    from: “The optical properties of pure water and pure sea water” by A. Morel (https://marine.rutgers.edu/pubs/private/morel1974-water.pdf)
     
  4. Oct 5, 2018 #3
    Why do you think that?

    https://en.wikipedia.org/wiki/Rayleigh_scattering
     
    Last edited by a moderator: Oct 5, 2018
  5. Oct 5, 2018 #4
    I’ll leave it to others to debate whether to call the scattering by the water molecules Rayleigh scattering or Einstein-Smurfsomebody scattering. However I thought I’d mention that in many of the most interesting places (within tens of meters of the surface, within tens or even hundreds of kilometers of most shores) most of the scattering is due to suspended particles which are larger than the wavelength of light and that part of the scattering is better explained by Mie theory.

    https://link.springer.com/chapter/10.1007/978-1-4684-8529-5_5
     
  6. Oct 6, 2018 #5

    Lord Jestocost

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  7. Oct 6, 2018 #6
  8. Oct 7, 2018 #7

    Lord Jestocost

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    One speaks of Rayleigh scattering in case of light scattering from molecules if the conditions for independent scattering on the single molecules are valid. When the molecules aggregate the situation changes: scattered waves coming from different parts of the aggregate interfere and partially extinguish each other. For aggregate sizes larger than a wavelength, Mie scattering predominates. And in case of a homogeneous, nonabsorbing bulk liquid you treat the interaction with light in terms of reflection and refraction.
     
    Last edited: Oct 7, 2018
  9. Oct 9, 2018 #8
    Do you have citation/evidence for this?

    Refraction and reflection occurs when light enters water. But it's unrelated with light propagation in water. The speed of light is a lot lower in water yet photons always move at c. This lower speed is due to light propagation in water. Photons scatter because of interaction with H2O. This interaction is called Rayleigh scattering.

    Do you have evidence for the presence of Mie scattering in light propagation in water?
     
  10. Oct 11, 2018 #9

    Lord Jestocost

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    When an ensemble of scattering centers exhibits some degree of short- or long-range ordering, scattered electromagnetic waves coming from different parts of the ensemble interfere and partially extinguish each other. Thus, the overall scattering pattern changes compared to the scattering pattern of a single scatter center. This is a fundamental consideration when treating scattering of electromagnetic waves in dense media. The final result is a cooperative effect of all involved scattering centers.
     
  11. Oct 11, 2018 #10
    Yes but do you have evidence?Citation?
    When watermolecules aggregate and form a liquid, they aggregate +/- homogeneously, they don't form spheres for Mie scattering.
    Mie scattering happens in clouds, not in liquid water.
     
  12. Oct 11, 2018 #11

    Lord Jestocost

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    Please, read comment #7 carefully: "For aggregate sizes larger than a wavelength, Mie scattering predominates. And in case of a homogeneous, nonabsorbing bulk liquid you treat the interaction with light in terms of reflection and refraction."

    So, where did I speak of "evidence for the presence of Mie scattering in light propagation in water"?

    When light "travels" through pure, homogeneous "bulk" water, you observe no Rayleigh scattering pattern (i.e. you don't speak of Rayleigh scattering).

    Of course, the individual water molecules act as scattering centers; but the overall effect is that the electrical wave does appear to travel at the speed c/n through water with the index of refraction n.
     
  13. Oct 11, 2018 #12
    I ask for evidence/citation but you refuse to give any.
     
  14. Oct 11, 2018 #13
    How do you know this?
    And how do you observe a Rayleigh scattering pattern?
     
  15. Oct 12, 2018 at 2:54 AM #14

    Lord Jestocost

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  16. Oct 12, 2018 at 4:09 AM #15

    DrClaude

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    Page 12 of that PDF summarises well the issue here.
     
  17. Oct 17, 2018 at 3:53 PM #16
  18. Oct 18, 2018 at 6:33 AM #17

    Lord Jestocost

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