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

• itoero
In summary, Rayleigh scattering is the scattering of light by smaller particles in liquids. This scattering is not accounted for by the Rayleigh theory, which is applicable to solids. The scattering is instead dominated by Mie scattering in liquids.
itoero
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

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)

berkeman
New
The Rayleigh theory is not applicable to liquids.
Why do you think that?

https://en.wikipedia.org/wiki/Rayleigh_scattering
Rayleigh scattering (pronounced /ˈreɪli/ RAY-lee), named after the British physicist Lord Rayleigh (John William Strutt),[1] is the predominantly elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation. Rayleigh scattering does not change the state of material and is, hence, a parametric process. The particles may be individual atoms or molecules. It can occur when light travels through transparent solids and liquids, and is most prominently seen in gases.

Last edited by a moderator:
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.

Lord Jestocost said:
A good explanation regarding the various scattering effects can be found on https://www.itp.uni-hannover.de/fileadmin/arbeitsgruppen/zawischa/static_html/scattering.html
Yes but why do you think Rayleigh theory is not applicable to liquids?
Rayleigh scattering is the mostly elastic scattering of light (or other elctromagn) by particles much smaller then the wavelength of the electromagnetic radiation.
Regardless of the medium you're in.

itoero said:
Yes but why do you think Rayleigh theory is not applicable to liquids?

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:
Lord Jestocost said:
When the molecules aggregate the situation changes: scattered waves coming from different parts of the aggregate interfere and partially extinguish each other
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?

itoero said:
Do you have citation/evidence for this?

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.

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.

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.

I ask for evidence/citation but you refuse to give any.

Lord Jestocost said:
When light "travels" through pure, homogeneous "bulk" water, you observe no Rayleigh scattering pattern
How do you know this?
And how do you observe a Rayleigh scattering pattern?

Lord Jestocost said:
Evidence for what? That scattered waves coming from different parts of a medium interfere with each other? That's basic physics. Have a look at
[PDF]
The Propagation of Light - Purdue Physics
Page 12 of that PDF summarises well the issue here.

Lord Jestocost said:
As water is in a physical sense a dense medium you can rely on the link The Propagation of Light - Purdue Physics
There are many types of dense media..
And you talked about mie scattering in water, which you still haven't given an y evidence for.
How can light propagate in water without photon-H2O-scattering?

itoero said:
There are many types of dense media..
And you talked about mie scattering in water, which you still haven't given an y evidence for.
How can light propagate in water without photon-H2O-scattering?
The interaction in liquid water will not be as simple as photon / molecule scattering because each water molecule is bound to its neighbours much more than when it's in the gaseous phase.
See #11

sophiecentaur said:
The interaction in liquid water will not be as simple as photon / molecule scattering because each water molecule is bound to its neighbours much more than when it's in the gaseous phase.
What kind of binding?
Clouds form when the invisible water vapour in the air condenses into visible water droplets, this causes Mie scattering but that's unrelated to light propagation in liquid water.

#### Attachments

3.6 KB · Views: 468
itoero said:
What kind of binding?
The individual molecules of water are bound to each other - otherwise it would be vapour and much lower density. That alters the energy situation doesn't it?

This thread is thrashing somewhat pointlessly. Thanks for participating.

Thread closed for moderation. If it is determined the thread can be saved we will reopen it again.

## 1. What is light propagation in water?

Light propagation in water refers to the way that light travels through water. This can be affected by factors such as the composition and turbidity of the water, as well as the angle and intensity of the light source.

## 2. How does light travel through water?

Light travels through water by interacting with the molecules and particles present in the water. This can result in absorption, reflection, and scattering of the light, which can affect its propagation through the water.

## 3. What is Rayleigh scattering?

Rayleigh scattering is a type of scattering that occurs when light waves interact with particles that are much smaller than the wavelength of the light. This type of scattering is responsible for the blue color of the sky and the blue tint of bodies of water.

## 4. Is Rayleigh scattering the only type of scattering in water?

No, there are other types of scattering that can occur in water, such as Mie scattering, which occurs when the particles in the water are similar in size to the wavelength of the light. However, Rayleigh scattering is the most common type of scattering in water.

## 5. How does Rayleigh scattering affect light propagation in water?

Rayleigh scattering can cause light to be scattered in all directions as it passes through water, which can result in a decrease in the intensity of the light. This can affect the visibility and color of objects in the water, as well as the amount of light that reaches deeper levels of the water.

• Optics
Replies
22
Views
1K
• Optics
Replies
4
Views
7K
• Optics
Replies
2
Views
1K
• High Energy, Nuclear, Particle Physics
Replies
12
Views
1K
• High Energy, Nuclear, Particle Physics
Replies
5
Views
987
• Optics
Replies
4
Views
1K
• Optics
Replies
1
Views
4K
• Optics
Replies
2
Views
16K
• Quantum Physics
Replies
25
Views
11K
• Optics
Replies
6
Views
3K