Fact: Red light penetrates deeper

[Subcooled]

I have experimental evidence of the fact that red light penetrates deeper than blue.

When I start my ascent from total darkness at 15 feet, the first light I will see is red.
Next, orange.
Then it becomes green.
And finally what I would call transparent and then I will break surface.

I would appreciate a proper physical explanation to this. Equations are more than welcome. Long wavelength radiation somehow penetrates muddy water better than short wavelengths.

Note that this is not pure water. Visibility is measured in inches. There are VAST AMOUNTS of suspended particles such as clay, mud and algae.

Water is sweet to brackish. Temperature is +7C. At sea level.

 

[rjack321]

The shorter wavelengths are scattered, the longer wavelengths penetrate. The shorter waverlengths scatter because for a given wave, they on average contact more water molecules. The UV spectrum is very rapidly scattered, the long wave heat, not nearly at all.

Ocean Physics at NASA - NASA Science

Science and Research NASA’s Ocean Physics program directs multiple competitively-selected NASA’s Science Teams that study the physics of the oceans. Below are details about each science team. Physical Oceanography (PO) Sea Level Change (N-SLCT) Ocean Surface Topography (OSTST) Surface Water and...

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[archman]

Light absorption patterns in more turbid waters work more like this.

 

[Subcooled]

The shorter wavelengths are scattered, the longer wavelengths penetrate. The shorter waverlengths scatter because for a given wave, they on average contact more water molecules. The UV spectrum is very rapidly scattered, the long wave heat, not nearly at all.

Ocean Physics at NASA - NASA Science

Science and Research NASA’s Ocean Physics program directs multiple competitively-selected NASA’s Science Teams that study the physics of the oceans. Below are details about each science team. Physical Oceanography (PO) Sea Level Change (N-SLCT) Ocean Surface Topography (OSTST) Surface Water and...

science.nasa.gov

"The shorter wavelengths are scattered, the longer wavelengths penetrate." is counterintuitive. In clear water photography there is a lack of reds. If long wavelengths would penetrate, red would be present, right? But no! Everything is blue!

Wikipedia, the ultimate reference, knows that "Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities".

 

[Subcooled]

The shorter waverlengths scatter because for a given wave, they on average contact more water molecules.

Electromagnetic radiation propagates spherically and interacts with atoms/molecules by exciting electrons on orbitals. That leads to emissions of radiations = reflection. This simple model I undestand.

Short wavelengths have more energy doing this. Hence more reflections. Light penetrates deeper. A lot of particles will block this though.

Red on the other hand, cannot excite, and cannot reflect that well (am I correct?). It just gets absorbed.

If the water is muddy, the we can understand the lack of reds. But what is the explanation of lack of blues.

 

[rjack321]

Electromagnetic radiation propagates spherically and interacts with atoms/molecules by exciting electrons on orbitals. That leads to emissions of radiations = reflection. This simple model I undestand.

Short wavelengths have more energy doing this. Hence more reflections. Light penetrates deeper. A lot of particles will block this though.

Red on the other hand, cannot excite, and cannot reflect that well (am I correct?). It just gets absorbed.

If the water is muddy, the we can understand the lack of reds. But what is the explanation of lcks if

The longest wavelengths are getting absorbed yes
The shortest are getting reflected (within mms)

I think the rest of your text was cut off somehow

 

[Subcooled]

[deleted - late night and wrong thinking]

 

[Akimbo]

Here is how it is described in the US Navy Diving Manual, Revision 7A, section 2-6.4, Page 2-6, Acrobat page 126:

Color Visibility. Object size and distance are not the only characteristics distorted underwater. A variety of factors may combine to alter a diver’s color perception. Painting objects different colors is an obvious means of changing their visibility by enhancing their contrast with the surroundings, or by camouflaging them to merge with the background. Determining the most and least visible colors is much more complicated underwater than in air.

Colors are filtered out of light as it enters the water and travels to depth. Red light is filtered out at relatively shallow depths. Orange is filtered out next, followed by yellow, green, and then blue. Water depth is not the only factor affecting the filtering of colors. Salinity, turbidity, size of the particles suspended in the water, and pollution all affect the color-filtering properties of water. Color changes vary from one body of water to another, and become more pronounced as the amount of water between the observer and the object increases.

The components of any underwater scene, such as weeds, rocks, and encrusting animals, generally appear to be the same color as the depth or viewing range increases. Objects become distinguishable only by differences in brightness and not color. Contrast becomes the most important factor in visibility; even very large objects may be undetectable if their brightness is similar to that of the background.

 

[Subcooled]

Look at these images (frames of video) from my 20 second ascent from 13 feet.
Ambient light turns from reddish brown to more orange, yellow, green, blue...
Similar succession of colors is visible to the naked eye, so this is not a camera white balance issue.

Red ambient light at depth:

A little bit shallower:

And shallower:

And shallower:

And shallower:

And shallower:

And shallower:

And just under the surface:

 

[Wibble]

The only place I’ve dived that was 'red' underwater was Loch Ness, famed for its peaty, tannin rich water.

In the sea you have to add back the red by using filters on ambient light cameras.

Just observations in real life.