The Sea-viewing Wide Field-of-view Sensor (SeaWiFS), an instrument that observes the world's oceans from space and monitors subtle changes in the color of the ocean that hint of larger flux under way, was launched on August 1, 1997, from Vandenburg Air Force Base, California. After a month of adjusting its orbit and a few weeks of testing data, SeaWiFS began providing the first pictures of ocean color taken in over 10 years and the first continuous look at the global biosphere ever (see cover photo), giving scientists a method for monitoring life on Earth.
Using satellite observations of ocean color, scientists can study the concentration of microscopic marine plants (phytoplankton). Color in most of the world's oceans in the visible light region (wavelengths of 400-700 nm) varies with the concentration of chlorophyll and other plant pigments present in the water; the more phytoplankton present, the greater the concentration of plant pigments. Ocean color data are critical for studying ocean primary production and global biogeochemistry. "Primary production" refers to the organic material in the sea that is produced by algae and some bacteria, the ocean's "primary producers." These organisms-which are at the lowest level of the food chain-use sunlight or chemicals rather than other organic material, as sources of energy. Marine plants are thought to remove carbon from the atmosphere as quickly as plants on land do, but present knowledge of variability on time scales longer than the seasonal cycle is very poor. Since SeaWiFS can view every square kilometer of cloud-free ocean every 48 hours, satellite-acquired ocean color data are valuable for determining the abundance of ocean biota on a global scale. The SeaWiFs data also can be used to assess the ocean's role in the global carbon cycle and the exchange of the other critical elements and gases between the atmosphere and the ocean.
In addition to helping scientists understand the carbon cycle, SeaWiFS will also be an important tool for conducting fisheries research and managing the coasts with respect to coastal cleanup, as pollutants and harmeful algae blooms can be detected from space.
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| Figure 1: The coastal region between Cape Canaveral and Cape Hatteras is called the South Atlantic Bight (SAB). Two features bound the shelf waters of the SAB. The first is the Gulf Stream, which has very low chlorophyll concentrations and is located on the offshore edge of the continental shelf until it reaches Cape Hatteras, where the current turns eastward. The second feature is the high concentration waters along the coast. The waters develop from coastal river, estuary, and marshland dishcharge throughout the SAB. Under ordinary conditions, the band of high-concentration coastal waters would be much wider, but the unusually dry summer has dramatically reduced the extent of this water mass. |
Near coastlines, ocean color is affected by suspended sediments, pollutants, and harmful algae blooms, such as red tides. Red tides are caused by several species of marine phytoplankton that produce potent chemical toxins. These toxins cause extensive fish kills, contaminate shellfish, and cause severe respiratory irritation in humans along the shore. Tracking nearshore ocean color will provide crucial data for environmental monitoring applications in the coastal zone. The ocean color data will also help to better understand processes associated with mixing of colder and warmer "layers" of water along the edges of eddies and boundary currents.
"SeaWiFS offers great potential for monitoring oceanic conditions and coastal blooms of algae that have serious, and often tragic, effects on human health. Early detection of these blooms, and subsequent in-water sampling, may potentially reduce the impact of such events. Red tides, ocean dumping of organic and chemical waste, and perhaps even oil spills can hopefully be tracked with SeaWiFS data," says Gene Carl Feldman, who heads SeaWiFS's data processing team.
As it turns out, SeaWiFS is giving the science community much more than ocean color data. It is providing the first continuous look at the global biosphere, giving scientists a way to monitor life on Earth for the first time. "The images are more than we ever could have hoped for," Feldman said. "Although originally designed to just study the oceans, we've also developed a way of using it to study the land as well, and as a result, can study the 'global biosphere' for the very first time." There are many hypotheses about how changes in temperature or climate will affect life forms, but until now there had not been a sensor to monitor it. "Other sensors have looked at factors that affect life on Earth, but no other sensor has monitored the distribution of life itself," Feldman said. "It's like a doctor who sees lab results without seeing the patient."
SeaWiFS will be used to research El Niño and global warming and monitor the environment of the ocean, observe phenomena that affect humans such as deforestation on land, and observe smoke in the atmosphere over such areas as Indonesia and the Amazon, where tropical rainforests are being burned and cleared.
"It will be possible to observe long-term changes in vegetative cover as humanity affects natural systems, such as the clearing of the tropical rain forests for agriculture. It will also be used to evaluate the impact of global-scale natural events such as El Niño on marine ecosystems," says SeaWiFS Project Scientist Charles R. McClain.
NASA released a global biosphere image in 1989. This earlier rendition combined data from two different satellites, one for the ocean and the other for land. But the data were collected several years apart, and even then many parts of the world were left unobserved.
Because the earlier biosphere data was a collage of different satellite imagery from different time periods, it could not be used to study changes in life on our planet over time. SeaWiFS data will make this possible. In addition, because there has never been a sensor that could study land, ocean, and atmosphere, there is a new possibility for cross-disciplinary studies of life on Earth. As with all new technologies, there is no telling what exciting results could follow.
Another groundbreaking element of the SeaWiFS Project is the speed with which the data is provided to the community. The SeaWiFS data were made available via the World Wide Web only minutes after the instrument was turned on.
SeaWiFS, which is led by NASA, is an international collaboration. Over 400 scientists in 39 countries are registered to use SeaWiFS data, which are received at 71 ground stations in 24 countries. Unlike most NASA missions, however, SeaWiFS was not built by NASA. "It's a whole new way of doing business," SeaWiFS Project Manager Mary Cleave says. Rather than building, launching, and controlling a satellite to study an important aspect of the Earth's environment, NASA is purchasing commercially available SeaWiFS data for environmental research.
The SeaWiFS Project has developed and operates a research data system that processes, calibrates, validates, archives, and distributes data received from the Earth-orbiting ocean color sensor. The satellite has a 5-year lifetime.
SeaWiFS is an essential component of the Mission to Planet Earth, an ongoing effort to study the changing global environment. SeaWiFS is a follow-on sensor to the Coastal Zone Color Scanner (CZCS), which operated aboard NASA's Nimbus-7 satellite from 1978 to 1986 and proved that satellite sensors could detect ocean color from space. Benefiting from the CZCS experience, SeaWiFS offers improvements that result in a more accurate determination of phytoplankton concentration. SeaWiFS has more bands and gives a clearer signal, and it has two near-infrared bands that offer an improved atmospheric correction scheme.
SeaWiFS images and data are available from the World Wide Web at: http://seawifs.gsfc.nasa.gov/seawifs.html.
| A Few Words From the Author | |
I became interested in studying physics during my junior year in college because I was fascinated with reading the works of Liebniz, Newton, and Faraday. I chose oceanography because my father was in the Coast Guard and I liked the sea. Also, while I was growing up, 'The Living Seas' exhibit at the EPCOT Center was a favorite of mine. I received a B.A. in liberal arts from St. John's College in Annapolis, Md., and an M.S. in physical oceanography from the University of South Florida in St. Petersburg. |
Science is an exciting field to work in because ideas in the field are new and constantly being tested or challenged. Oceanography is especially exciting because it's a relatively young science. We've spent more time on the surface of the Moon than in Earth's deep oceans! So, my advice to those students interested in science is to go for it!! Also, you don't have to wait until college. There are many summer programs and internship available for students: take advantage of them. |