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Abstract
An airplane provides great opportunities to view the colors and patterns of light scattered and reflected from water. Pure water lit by sunlight appears blue when it is deep enough that you do not see light reflected from the bottom (Fig. 7.1). Shallow water near the middle of Fig. 7.1 and in Fig. 7.2 allows light reflected from the bottom to mix with the scattered blue light, creating shades of blue-green and green. The dark patches are either regions of cloud shadow (Fig. 6.19) or shallow regions with a darker-colored underwater surface. Figure 7.3 is a plot of the scattering coefficient (dashed line) and absorption coefficient (solid line) for pure water, showing that the pure blue color of deep water is the result of scattering from water molecules (very similar to scattering by air molecules) and that red light is removed by absorption. The vivid colors that can be seen in hot pools of water at Yellowstone Park result from the same mechanisms but with greater variety due to the microbial mats that coat the surfaces of all but the hottest thermal pools. The water color is not influenced strongly by the sky color except when viewing water near the horizon, at which angle the surface strongly reflects skylight. Water also can assume a milky green appearance from scattering by small suspended particles. For example, the famous turquoise-green color of Bear Lake on the Idaho–Utah border is primarily a result of scattering from suspended calcium carbonate particles (Fig. 7.4). Similarly, the milky green color of Blanca Lake in the Cascade Mountains of Washington State is caused by the scattering of light from small particles of glacial till (Fig. 7.5). The green swirls in the satellite image of the Barents Sea (Fig. 7.6) are the result of scattering from coccolithophores and possibly other phytoplankton - tiny micro-organisms that form an important component at the bottom of the marine food chain. Large quantities of silt carried down from the Alaska Range turn the water of the Tanana River in central Alaska brown (Fig. 7.7). An incredible billowing pattern can be seen from up close at the point where the silt-laden Tanana River meets the smaller and clearer Chena River (Fig. 7.8). A less turbulent mixing of silty brown water with the milky green water of Bear Lake is seen in Fig. 7.9
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CHAPTER 7
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