Light Attenuation in Water
Shortwave radiation emitted from the sun wavelengths in the visible spectrum of light that range from 360 nm (violet) to 750 nm (red). When the sun’s radiation reaches the sea-surface, the shortwave radiation is attenuated by the water, and the intensity of light decreases exponentially with water depth. The intensity of light at depth can be calculated using the Beer-Lambert Law.
In clear open waters, visible light is absorbed at the longest wavelengths first. Thus, red, orange, and yellow wavelengths are absorbed at higher water depths, and blue and violet wavelengths reach the deepest in the water column. Because the blue and violet wavelengths are absorbed last compared to the other wavelengths, open ocean waters appear deep-blue to the eye.
In near-shore (coastal) waters, sea water contains more phytoplankton than the very clear central ocean waters. Chlorophyll-a pigments in the phytoplankton absorb light, and the plants themselves scatter light, making coastal waters less clear than open waters. Chlorophyll-a absorbs light most strongly in the shortest wavelengths (blue and violet) of the visible spectrum. In near-shore waters where there are high concentrations of phytoplankton, the green wavelength reaches the deepest in the water column and the color of water to an observer appears green-blue or green.
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Famous quotes containing the words light and/or water:
“Long enough I had heard of irrelevant things; now at length I was glad to make acquaintance with the light that dwells in rotten wood. Where is all your knowledge gone to? It evaporates completely, for it has no depth.”
—Henry David Thoreau (1817–1862)
“It is the work of a brave man surely, in whom there was no guile! He rounded this water with his hand, deepened and clarified it in his thought, and in his will bequeathed it to Concord. I see by its face that it is visited by the same reflection; and I can almost say, Walden, is it you?”
—Henry David Thoreau (1817–1862)