Green Reflections

May 21, 2007

Mustangridgesagpond

Provided and copyright by: David Lynch, Thule Scientific
Summary authors & editors: David Lynch

This bucolic scene of central California pastureland (on Mustang Ridge, along CA-198 and near the boundary of Monterey and San Benito Counties) reveals some odd reflections. The pond looks normal, reflecting blue skylight. But the reflections of the surrounding trees are bright green. Normally, a reflected scene in still water looks very much like the original, just upside down and slightly darker because the water doesn't reflect 100% of the light. Here, the reflected trees aren't the same color as the original trees and certainly aren't any darker. How can this be?

To answer the question, you have to ask “Where does the light originate that I see coming from a body of water?” It can be from surface reflections, light scattered from the volume of the water itself, or it can come from light reflected from the surface at the bottom of the water. It can also come from light scattered from dust that floats on the water’s surface. Depending on the depth, clarity and angle of the line of sight, any one of the above sources can dominate what we see. In most cases, several contribute at once. Light coming from water is far from simple!

In this case, the pond water is filled with green algae. Its not apparent where blue skylight is reflected because the sky is so bright. But in the dim reflections of the dark trees, the sunlit algae-laden water is clearly evident. The pond, by the way, is a sag pond directly on the San Andreas Fault, but this has nothing to do with the color of the water. Photo taken in May of 2004.

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