Why So Blue?

Title

Why So Blue?

Artist

Jon Burch Photography

Medium

Photograph - Digital Capture/textured

Description

Visibility under water depends on the amount of light reaching the particular depth. Illumination itself depends on the thickness of the water layer and on the reflection and scatter of light rays in the water medium. Part of the light coming from the sun is reflected by the surface of the water and the amount of reflected light depends on the angle between the rays and the surface of the water, also, on the quantity of air bubbles in the surface layer that have been formed by the motion of the water

The most important reason for the low visibility under water is the weakening of the refraction capability of human eyes. In the open air, it is sufficient because the refraction quotient of light is 1 and that of the human optical system is 1.38. Water has a refraction quotient of 1.33, very close to that of the eyes

Light is absorbed as it passes through the water, and much of it is lost in the process. In addition, the spectral components of light, the wavelengths that give rise to our perception of color, are differentially absorbed. Transmission of light through air does not appreciably change its spectral composition, but transmitting light through water, even the clearest water, does, and this can change the resulting color appearance beyond recognition. In clearest water, long wavelength or red light is lost first, being absorbed at relatively shallow depths. Orange is filtered out next, followed by yellow, green, and then blue. Other waters, particularly coastal waters, contain silt, decomposing plant and animal material, and plankton and a variety of possible pollutants, which add their specific absorptions to that of the water. Plankton, for example, absorbs violets and blues, the colors transmitted best by clear water. The amount of material suspended in some harbor water is frequently sufficient to alter the transmission curve completely; not only is very little light transmitted, but the long wavelengths may be transmitted better than the short, a complete reversal of the situation in clear water

Color vision under water, whether for the visibility of colors, color appearances, or legibility, is much more complicated than in air. Accurate underwater color vision requires the knowledge of the colors involved, understanding the sensitivity of the eye to different colors, know the depth and underwater viewing distance.

Changes occur too in the appearance of colors under water. For example, red objects frequently appear black under water. This is readily understandable when one considers that red objects appear red on the surface because of reflected red light. Since clear water absorbs the red light preferentially, at depth no red light reaches the object to be reflected, and therefore the object appears unlighted or black. In the same way, a blue object in yellowish-green water near the coast could appear black. Substances that have more than one peak in their reflectance curve may appear quite different on land and in the sea. Blood is a good example; at the surface a reflectance maximum in the green is not noticeable because there is a much larger one in the red. At depth, the water may absorb the long wavelength light and blood may appear green. The ghostly appearance of divers in 20 to 30 feet of clear water is another example of the loss of red light.

In general, less and less color is perceived as the depth and viewing distance under water are increased, and all objects tend to look as though they are the same color. Objects must then be distinguished by their relative brightness or darkness. Many of the most visible colors are light, bright colors that give good brightness contrast with the dark water background. If the background were different than the object being observed, darker colors would have increased visibility. Fluorescent colors are conspicuous under water because fluorescent materials convert short wavelength light into long wavelength colors that are rarely present under water, which increases the color contrast.

Image made with a Canon 5D MKIII camera from a submarine off of Oahu.

Photograph copyright Jon Burch Photography

Uploaded

June 14th, 2013

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