Classic CZCS Scenes describes this and other images. When visible light from the Sun illuminates the ocean surface, it is subject to several optical effects. Foremost among these effects are light reflection and absorption. Reflection beneath the water surface is generally inefficient, returning only a small percentage of the light intensity falling on the ocean surface. Absorption selectively removes some wavelengths of light while allowing the transmission of other wavelengths.
Radiometers are instruments that measure the radiance intensity at a given wavelength of light.
The measured radiance may then be quantitatively related to various constituents in the water column that interact with visible light, such as chlorophyll. The concentration of chlorophyll, in turn, may be used to calculate the amount of carbon being produced by photosynthesis, which is termed primary productivity. The advantage of observing the oceans with a space-based spectroradiometer is the global coverage that a satellite provides. The disadvantage is that interfering optical effects, primarily light scattering in the atmosphere, must be accounted for to provide an accurate measurement of the water-leaving radiance. For a more detailed explanation of the data that is produced by SeaWiFS, read the SeaWiFS Data Set Readme document .