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The "color" of the ocean is determined by the interactions of incident light with substances or particles present in the water. White light from the sun is made up of a combination of colors, which are broken apart by water droplets in a ‘rainbow’ spectrum. Large quantities of water, even in a swimming pool, would appear blue as well. When light hits the water surface, the different colors are absorbed, transmitted, scattered, or reflected in differing intensities by water molecules and other so-called optically-active constituents in suspension in the upper layer of the ocean. The reason open ocean waters often appear blue is due to the absorption and scattering of light. The blue wavelengths of light are scattered, similar to the scattering of blue light in the sky but absorption is a much larger factor than scattering for the clear ocean water. In water, absorption is strong in the red and weak in the blue, thus red light is absorbed quickly in the ocean leaving blue. Almost all sunlight that enters the ocean is absorbed, except very close to the coast. The red, yellow, and green wavelengths of sunlight are absorbed by water molecules in the ocean. When sunlight hits the ocean, some of the light is reflected back directly but most of it penetrates the ocean surface and interacts with the water molecules that it encounters. The red, orange, yellow, and green wavelengths of light are absorbed so that the remaining light we see is composed of the shorter wavelength blues and violets. If there are any particles suspended in the water, they will increase the scattering of light. In coastal areas, runoff from rivers, resuspension of sand and silt from the bottom by tides, waves and storms and a number of other substances can change the color of the near-shore waters. Some types of particles can also contain substances that absorb certain wavelengths of light, which alters its characteristics. For example, microscopic marine algae, called phytoplankton, have the capacity to absorb light in the blue and red region of the spectrum owing to specific pigments like chlorophyll. Accordingly, as the concentration of phytoplankton increases in the water, the color of the water shifts toward the green part of the spectrum. Fine mineral particles like sediment absorb light in the blue part of the spectrum, causing the water to turn brownish in case of massive sediment load. The most important light-absorbing substance in the oceans is chlorophyll, which phytoplankton use to produce carbon by photosynthesis. Due to this green pigment - chlorophyll - phytoplankton preferentially absorb the red and blue portions of the light spectrum and reflect green light. Ocean regions with high concentrations of phytoplankton will have shades of blue-green depending upon the type and density of the phytoplankton population there. The basic principle behind the remote sensing of ocean color from space is that the more phytoplankton is in the water, the greener it is. There are other substances that may be found dissolved in the water that can also absorb light. Since these substances are usually composed of organic carbon, researchers generally refer to these substances as colored dissolved organic matter. ==Ocean colour radiometry== Ocean colour radiometry is a technology, and a discipline of research, concerning the study of the interaction between the visible electromagnetic radiation coming from the sun and aquatic environments. In general, the term is used in the context of remote-sensing observations, often made from Earth-orbiting satellites. Using sensitive radiometers, such as those on-board satellite platforms, one can measure carefully the wide array of colors emerging out of the ocean. These measurements can be used to infer important information such as phytoplankton biomass or concentrations of other living and non-living material that modify the characteristics of the incoming radiation. Monitoring the spatial and temporal variability of algal blooms from satellite, over large marine regions up to the scale of the global ocean, has been instrumental in characterizing variability of marine ecosystems and is a key tool for research into how marine ecosystems respond to climate change and anthropogenic perturbations. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ocean color」の詳細全文を読む スポンサード リンク
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