From the Top of the World...

Satellites in orbit provide a better than "birds-eye" view of our planet. Because of this perspective, satellites are extremely useful for making large-scale measurements of the ocean. Remote sensing is the term used to describe the process of making measurements from a distance. Remote sensing and in situ ("in place") measurements complement one another. With well-studied localized in situ measurements, scientists can use satellite data to create comprehensive, calibrated models of the ocean environment. Although the cost of building and launching a satellite can be great, the amount of data obtained by such satellites is so vast that the cost of individual data sets is often relatively small. In addition, they provide global coverage which is crucial to understanding the ocean environment. New computer, sensor, and electronic technologies are further reducing the cost of building satellites, and satellite ocean data are expected to become less expensive and even more powerful in the future.




	<< SeaWiFS satellite view of U.S. Pacific Northwest (courtesy of NASA)

	Satellites in orbit provide a better than "birds-eye" view of our planet. Because of this perspective, satellites are extremely useful for making large-scale measurements of the ocean. Remote sensing is the term used to describe the process of making measurements from a distance. Remote sensing and in situ ("in place") measurements complement one another. With well-studied localized in situ measurements, scientists can use satellite data to create comprehensive, calibrated models of the ocean environment. Although the cost of building and launching a satellite can be great, the amount of data obtained by such satellites is so vast that the cost of individual data sets is often relatively small. In addition, they provide global coverage which is crucial to understanding the ocean environment. New computer, sensor, and electronic technologies are further reducing the cost of building satellites, and satellite ocean data are expected to become less expensive and even more powerful in the future.


PHYTOPLANKTON, PIGMENTS & PHOTOSYNTHESIS
	Using instruments that are more sensitive than the human eye, we can measure carefully the wide array of colors of the ocean; and if you think that the ocean is "just blue-green," check out the variety of blue-green colors at your local paint store (<<<). From ocean color, we can infer information about phytoplankton populations. Phytoplankton contain various colored pigments such as chlorophyll; thus, ocean color signifies various types and geographic concentrations of phytoplankton. Phytoplankton blooms -- the rapid growth of a phytoplankton population -- are often marked by high concentrations of chlorophyll, a chemical compound crucial for photosynthesis. Knowing the locations of these blooms is very valuable to fishermen and marine biologists, because fish and other marine animals tend to collect near fresh blooms.

CHANGES IN OCEAN COLOR OVER TIME
Comparing satellite images taken at different periods tells us about changes that occur over time. Such satellite instruments include NASA's Coastal Zone Color Scanner (CZCS) that flew from 1978 to 1986, the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) which was launched in August 1997, and the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Earth Observing System's Terra satellite (launched in December 1999). Data from these instruments are helping scientists discover which phytoplankton species are involved in phytoplankton blooms.
Satellite-based ocean color data are also helping to improve our understanding of the ocean's role in the global carbon cycle. The atmosphere is a rich source of carbon dioxide (CO2), as millions of tons of this gas settle into the ocean every year. Phytoplankton use sunlight and CO2 to make food and grow. When they die, their bodies settle to the ocean bottom. Consequently, over geological time, the ocean has become the primary storage sink for atmospheric CO2. About 90 percent of the world's total carbon content has settled to the bottom of the ocean, primarily in the form of dead biomass. Click here to see a movie about this process (2.1 MB, Courtesy Barbara Summey, NASA/Goddard Space Flight Center)
Some background material from NASA Earth Observatory AND* "Visit to an Ocean Planet" CD-ROM, Copyright 1998, California Institute of Technology and its licenses.*