We see color when light is reflected by objects around us. White light is made up of a spectrum or combination of colors, as in a rainbow. When light hits the surface of an object, these different colors can be reflected or absorbed in differing intensities. The color we see depends on which colors are reflected and which are absorbed. For example, a book that appears red to us absorbs more of the green and blue parts of the white light shining on it, and reflects the red parts of the white light.
When we look at the ocean from space, we see many different shades of blue. Using instruments that are more sensitive than the human eye, we can measure carefully the fantastic array of colors of the ocean.
Different colors may reveal the presence and concentration of phytoplankton, sediments, and dissolved organic chemicals. Phytoplankton are smaIl, single-celled ocean plants, smaller than the size of a pinhead. These plants contain the chemical chlorophyll. Plants use chlorophyll to convert sunlight into food using a process called photosynthesis. Because different types of phytoplankton have different concentrations of chlorophyll, they appear as different colors to sensitive satellite instruments such as the Sea-viewing Wide Field-of-View Sensor (SeaWiFS). Thus, looking at the color of an area of the ocean allows us to estimate the amount and general type of phytoplankton in that area, and tells us about the health and chemistry of the ocean. Comparing images taken at different periods tells us about changes that occur overtime.