Coastal Observations: a Biological Perspective

Ocean Color and Satellite Imagery

When we think of the ocean, we think blue. However, it isn't just blue. The "color" of the ocean depends on the color of light reflected by the object in the water. Phytoplankton are the most significant constituents in determining the ocean color. Because phytoplankton contain chlorophyll, they absorb light at blue and red wavelengths and backscatter the green. Because green is reflected back, that is why the ocean looks green in color. Also, when we look at the satellite image of the ocean, different shades of blue make up the ocean. These different colors may represent the concentrations of phytoplankton, sediments, and dissolved organic chemicals. Because different types of phytoplankton have different concentrations of chlorophyll, they appear as different colors to sensitive satellite instruments.

The principal oceanographic motivation for observing ocean color from space is to permit better understanding of the role of the ocean in the global carbon cycle. Variability in the optical properties of the ocean influences the color of the ocean as seen from space. For most of the ocean, the optical properties are controlled by the concentration of biogenic particles and dissolved matter like phytoplankton, bacteria, and their degradation products. Variations in the optical properties modify the spectral and geometrical distribution of the underwater light field, and thereby alter the color of the sea. Biologically rich and productive waters are characterized by green water. Some of the research that uses ocean color will help to quantitatively specify the ocean's role in the global carbon cycle and other major biogeochemical cycles, and help determine the magnitude and variability of annual primary production by marine phytoplankton on both local and global scales, and their role in modifying the chemical and physical processes of the ocean and the atmosphere.

The images in the following sections were provided by the SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE.