SCIENCE FOCUS: MORE THAN MEETS THE EYE, PART 1

More Than Meets the Eye

The image shown on this page was created from remote sensing data obtained by SeaWiFS on January 15, 2001. The image covers much of the Argentinian coast, from the muddy-brown estuary of the Rio de la Plata in the north to the Falkland Islands and Patagonia at the southern tip of South America to the south. The city of Buenos Aires is located on the southern coast of the Rio de la Plata estuary. Two other coastal features are labeled on this image: Bahia Blanca, a turbid coastal area, and the clear water, dark blue Gulf of San Matias. These two areas show that diverse ocean optical conditions can be located in close geographical proximity.

The Gulf of San Matias is an important ecological area, due to its protected deep cold waters: it is the main breeding site for the southern right whale, one of the most endangered whales in the world, and supports large populations of seabirds, penguins, sea lions and elephant seals. Much of the land around the gulf is part of the Patagonian coastal steppe, with a unique population of land animals including guanacos (a species of wild llama), Patagonian foxes, maras (the Patagonian hare), puma, burrowing owls, peregrine falcons, flamingos, hairy armadillos, rheas, and burrowing parrots. Because there are no national parks or preserves in this area, it is endangered by sheep farming. However, some conservation groups have recently initiated programs to purchase large tracts of privately-held land for conservation purposes.

This image was selected to illustrate our Science Focus! article on SeaWiFS data analysis due to the variety of oceanographic and atmospheric conditions it contains. Near Bahia Blanca, smoke may be carried seaward from grass fires. The sediment-laden waters of the Rio de la Plata challenge the most sophisticated analytical algorithms.

One of the most prominent features in this image is the bright blue-green phytoplankton bloom that winds from the southeast to the northeast of the Falkland Islands. Due to the color of this bloom, and the cold water environment, this feature appears to be a coccolithophore bloom. Coccolithophores, the most common of which is a species named Emiliania huxleyi, are phytoplankton that create microscopic plates of calcium carbonate (CaCO₃) called coccoliths. The coccolithophores cement these plates around them to form a coccosphere. The presence of millions of microscopic pure-white coccospheres in the water, as well as free-floating coccoliths, creates an very bright and reflective ocean optical condition. Due to their brightness, coccolithophore blooms can cause ocean optical algorithms, intended to calculate chlorophyll concentration and other parameters, to produce erroneous results.

The SeaWiFS image shown here is an example of a "Level 1A" image. It was created using the radiances from three SeaWiFS bands (approximately red, green, and blue) and combining them to produce nearly natural colors. For this image, some of the effects of light scattering by the atmosphere were corrected, so the colors appear more vivid than if they would be if viewed from space at the orbital altitude of SeaWiFS.

Note in this image that the possible smoke appears gray and somewhat transparent compared to the brighter white of atmospheric clouds. Data processing is capable of removing some haze and smoke. So the first step in further analysis of this data is to process the data from Level 1A, the radiance data obtained by the satellite, to Level 2.

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