Fact: Red light penetrates deeper

[Subcooled]

A video can be seen here:

 

[Subcooled]

The U. S. Navy Diving Manual states:
"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."

My video shows the exact opposite.

Something quite interesting is happening in water with a high concentration of suspended matter


The manual also states:
"Light rays are diffused and scattered by the water molecules and particulate matter. At times diffusion is helpful because it scatters light into areas that otherwise would be in shadow or have no illumination."


It is true indeed that light behaves like a wave as can be seen from the double-slit experiment: Double-slit experiment - Wikipedia. It is clear then how light can diffuse in water and travel beyond all the suspended particles. It appears to me that when the concentration of suspended matter is high enough, long wavelengths travel farther, which reminds me of the first reply to this thread!


I have some reading to do to understand this a bit better.

 

[Wibble]

A video can be seen here:

Tannins in the water from plant life stain the water brown, filtering other colours

 

[Subcooled]

Tannins in the water from plant life stain the water brown, filtering other colours

Hm. There is indeed a lot of organic matter in the water, e.g. sinking blue-green algae and also anything that is washed to the sea from muddy fields.

 

[Wibble]

The tannins literally suck the light out of the water. Example here in Loch Ness. It was sunny on top, but at 2m/6' it was brown and by a mere 9m/30' it's pitch black. I'm pointing a bright torch out in front and it hardly penetrates the clear water. Was really eery, knowing there's a monster lurking in the darkness.

 

[archman]

Most of the light absorption descriptions written for scuba divers (and the general public) are simple, generic models that only apply to clear oligotrophic waters. Once you add particulates into the water (and a couple of other confounding variables also, like seafloor bottom type, water density, etc...) , those generic clear water descriptions no longer apply. If the water is really turbid, oceanographers and limnologists will just chuck the whole generic model out completely. We don't use it. We'll use specific models that best fit with the local environmental parameters, or if there isn't one, we'll create the local model ourselves.

 

[Akimbo]

This is interesting. In relatively clear water, like California's Pacific coast or in the middle of the North Sea, ambient color loss was consistent with the description in the Navy Manual. Blue could still be perceived around 165'/50M but it was virtually monochrome by 200-225'/60-68m.

Here is an ambient-light image I took in Truk Lagoon at about 165'/50M.

The water in the lagoon isn't nearly as clear as many tropical sites like Palau, but clearer than the Pacific coast or the North Sea, except for the very clearest days.

The physics of the light spectrum in pure water, like in a remote mountain lake, is little different than in high-visibility seawater like far offshore in the tropics. It changes pretty noticeably as visibility diminishes like on the Northeast US Atlantic coast.

 

[Subcooled]

Was really eery, knowing there's a monster lurking in the darkness.
View attachment 689721

Yes, I can see the monster! Upper right hand quarter, in the middle. I have been to Scotland twice. Once following whisky trail and staying overnight on Ben Macdui, once on a more leisurely road trip. Unfortunately, I never had the chance to dive Loch Ness.

We have huge amounts of dive sites with similar visibility here in Finland! Welcome! You will feel just like home! Albeit no monster! Diesel oil in the water? Yes! A dump in the water? Yes!

This type of light is typical for all of our dive sites.

 

[sea_ledford]

You are stating your ascent from a shallow enough depth that red still penetrates the water column. The particles in the water are reddish brown in color (ie they are absorbing all the other colors), so it is filtering the light you are seeing. As you move away from the bottom and into more clear surface water, the typical blue green color is evident.

I imagine as you go deeper, it just gets black. The particulates are absorbing all the non-reds, and the water absorbs all the red at about 15 feet.

 

[Angelo Farina]

Light filtering in muddy water strongly depends of the optical properties of the material in suspension.
It can be clay, mud, algae, etc.
Different materials filter light very differently, and this fact is exploited for analyzing the suspension in a lab instrument called a spectrophotometer.
Said that, here in Italy there is an alpin lake, named Tovel, in the wonderful dolomites, which during a period of the year used to become red, due to a rare species of alga. Unfortunately this species is now defunct...