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On Wikipedia I have found the following image:

enter image description here
The Japan Maritime Self-Defense Force (JMSDF) destroyer JDS Kongō (DDG 173) sails in formation with other JMSDF ships and ships assigned to the USS Kitty Hawk Carrier Strike Group. Wikimedia Commons. Public domain image.

As you can see the water behind the ships is very neatly light blue, but the sky is much more colored like the rest of the ocean. Is this an effect like HDR or plain photoshop (post processing)?

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Is this an effect like HDR or plain photoshop (post processing)?

I'd say neither. The effect is natural. The ships' propellors churn the water quite a bit, causing the wake to become aerated. This is obvious from the white caps on the surface. But the aeration also extends below the surface. Aerated water like that tends to appear lighter shades of blue and blue-green.

The description of the file at Wikimedia Commons states that it was taken in late 2005 by US Navy Chief Photographer's Mate Todd Cichonowicz. While there might have been some post-processing, it was probably very little, considering the year the image was produced. Any HDR processing or other unconventional tricks would be required to be disclosed in the image's credit line per U.S. Department of Defense policy.

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    \$\begingroup\$ Navy policy for their photojournalists is that they are not even allowed to crop images under most circumstances (if the usage calls for a different aspect ratio, that task falls to the editor, not the photographer), so I highly doubt that they would release an image that had been overly processed to make the scene appear different that it more or less appeared to the eye at the time. \$\endgroup\$
    – Michael C
    Oct 5, 2020 at 18:15
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    \$\begingroup\$ @MichaelC Yeah, it's a bit like several reporting or wire services, Nat Geo, etc., that only take JPEGs straight out of camera. I was wondering if this was for a PR photo, that perhaps it might have been sharpened, cropped, but that's about it. \$\endgroup\$
    – scottbb ♦
    Oct 5, 2020 at 20:09
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    \$\begingroup\$ The answers on Quora attribute the coloration to phytoplankton, rather than simply to aeration of the water. Is there any way to choose one or the other explanation? \$\endgroup\$
    – Ruslan
    Oct 5, 2020 at 20:33
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    \$\begingroup\$ Very interesting answer and comments. I've spent quite some time digging through articles and images of ships in rainy or stormy conditions. For civilian ships I could only find one image where below the white mist you can see some turquoise like in the OP image. However for several military ships similar colors could be observed, so I assume it is really natural and just due to neglecting fuel efficiency and the environment over warlike conditions :-) \$\endgroup\$
    – Yanick Salzmann
    Oct 5, 2020 at 21:45
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    \$\begingroup\$ If the OP is referring to the wake, this is more of a physics question than a photography one. Just because someone takes a picture of a phenomenon shouldn't make it on-topic. Given that this is Photography SE, I was expecting a question along the lines of "Why is the water on the horizon bluer than the water close to the camera?" \$\endgroup\$
    – Acccumulation
    Oct 6, 2020 at 6:05
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Many navy ships intentionally inject air into their wake to obfuscate their sonar signature. See Prairie-Masker air system

This added air gives the wake a light blue hue, and since the air bubbles are small they persist for quite some time. I served on a US Navy ship and can attest that the color in this photo accurately depicts what our wake looked like.

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    \$\begingroup\$ Random tidbits of information are great, but this isn't an answer to the question. Downvoting, sorry. \$\endgroup\$
    – osullic
    Oct 7, 2020 at 22:03
  • \$\begingroup\$ Edited to make it more "answer-y". \$\endgroup\$
    – Crash Gordon
    Oct 8, 2020 at 16:09
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As Scotbb answered, it is casued by aeration of the water.

Air is usually colourless and thus mixed with any coloured substance it makes the tone lighter, with respect to the ratio.

Propeller mixes the waters with air forming bubbles of various sizes, the bigger the bubble is the easier it gets to the surface and pops.

I expect the boats go on full throtle meaning higher mixing with air and forming a lot of micro bubbles that "float" in the water thanks to low buyoancy of the bubble and high viscosity of the surrounding water.

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    \$\begingroup\$ Colorless does not make any difference... it can't be added to anything. And air is not white, which would make a tone lighter. The bubbles/froth/wake are white because the air causes a very low density of water there, which causes the water to be much less absorptive of visible light; and therefore, they reflect more/all of the visible spectrum (angle of incidence/reflectance dependant). \$\endgroup\$
    – Steven Kersting
    Oct 6, 2020 at 13:35
  • \$\begingroup\$ The water density is given by temperature and salinity, mostly. The coroulesness of the air bubbles are the cause the water/bubble mixture absorbs less light but of same spectrum. Plus the round water/air interface reflects light as well. Was the air of some colour, it would shade the "tail" towards it's tone. \$\endgroup\$
    – Crowley
    Oct 7, 2020 at 15:45
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The light blue stuff you're seeing are the white bubbles caused by the churn of the ships' propellers.

Water is blue; it absorbs other wavelengths of light to a greater extent than it absorbs blue wavelengths. If you place a long tank of water between you and a white light source, the light source will appear blue. The longer the tank, the more water there is between you and the light, thus the greater the absorption of light and the darker & bluer the water appears.

The water around the ships appears very dark blue because the light from the sky travels deep into the water and is mostly absorbed, leaving little to reflect back into the camera. Whereas the light hitting the white bubbles is mostly reflected into the camera after passing through mere metres of water; however, a little is absorbed. Thus the bubbles appear light blue instead of white.

If the ships were not causing bubbles but dragging bunches of white ribbons a few metres under the surface behind them, those ribbons would appear a similar light blue.

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Given the relatively low ambient light level (the scene is very overcast) it may also be a result of bioluminescence.

Quote: "Among the anecdotes of navigation by bioluminescence is one recounted by the Apollo 13 astronaut Jim Lovell, who as a navy pilot had found his way back to his aircraft carrier USS Shangri-La when his navigation systems failed. Turning off his cabin lights, he saw the glowing wake of the ship, and was able to fly to it and land safely."

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    \$\begingroup\$ From my own experience from scuba diving: that kind of biolumiscence is only visible when it is pretty dark. \$\endgroup\$
    – Kai Mattern
    Oct 8, 2020 at 10:55
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It's called bioluminescence from disturbed plankton, it's very common but more viable at night. It's like a giant blue or green Aaron pointing at them back of the ship.

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  • \$\begingroup\$ Are you able to provide a source for this statement, in particular one that refutes the idea that it's just simple aeration of the water behind the ship? \$\endgroup\$
    – Philip Kendall ♦
    Sep 12 at 11:23
  • \$\begingroup\$ bioluminescent plankton isn't visible during daylight though. And it's only visible in ships' wakes at night sometimes, depending on algal concentrations, temperature, conditions of the water column, etc. Whereas, the color-lightening effect in ships' wakes is always visible when ships are moving at speed. Even at night, when you don't see any bioluminescent glow, the water will appear a lighter shade of blue or green. \$\endgroup\$
    – scottbb ♦
    Sep 13 at 23:44

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