On October 4, 1957, the Soviet Union successfully launched Sputnik I, the world's first artificial satellite. About the size of a basketball, and weighing only 183 lbs, Sputnik took about 98 minutes to orbit the Earth. While small and limited in function (It carried a tiny radio beacon that beeped at regular intervals.), the Earth's first artificial satellite ushered in an age of exploration not only of space, but of the Earth's land masses and oceans as well.
GOES-3 Satellite. Click image for larger view.
GOES-2 Satellite before launch. Click image for larger view.
Satellites that detect and observe different characteristics and features of the Earth's atmosphere, lands, and oceans are often referred to as environmental satellites. Most environmental satellites have one of two types of orbits: geosynchronous or sun-synchronous. Geo-synchronous satellites orbit the Earth at a speed matching the Earth's rotation. This allows them to hover continuously over one position on the surface. Most satellites used for communications, television, etc., maintain a geo-synchronous orbit. Geo-synchronous environmental satellites are used primarily for weather forecasting. These satellites orbit the earth about 22,000 mi directly over the equator, allowing them to continuously observe one side of the Earth. They are used to monitor the development of major storms, such as hurricanes, nor'easters, and tornadoes. The first of NOAA’s geo-stationary operational environmental satellites (GOES) was launched in 1975. Currently, GOES-8 and GOES-10 are operating, one for the western portion of the United States, the other for the Eastern portion.
Sun-synchronous satellites pass over a point on the Earth at the same time each day. The sun-synchronous environmental satellites are “polar orbiting,” meaning that they orbit the Earth from north to south, passing over the North and South Poles during each orbit. POES (Polar Operational Environmental Satellites) maintain an orbital height of about 500 mi and take about 100 min to complete an orbit. Depending on which sensors the satellite maintains on board, it may view a swath of only a few mi wide to one that is more than 1500 mi wide. Several types of satellites fall into this category, including NOAA's polar-orbiting environmental satellites (POES), Landsat, SeaWiFS, IKONOS, and others.
Sea surface-temperature is one important type of data that GOES and POES provide. Knowing the temperature of ocean water is important in and of itself. Temperature changes influence the behavior of fish, can cause the bleaching of corals, and affects weather along the coast. Satellite images of sea-surface temperature also show patterns of water circulation. Examples include locations of upwelling, characterized by cold waters that rise up from the depths, often near the coasts; and warm water currents, such as the Gulf Stream. The most commonly used instrument providing information on sea surface temperatures is the Advanced Very High Resolution Radiometer (AVHRR) on the NOAA meteorological satellites, NOAA-14, NOAA-15, and NOAA-16. This sensor collects data every day, creating an image by combining rows of 2,048 pixels (picture elements, or "dots") as it passes over the Earth’s surface. Each individual pixel taken by the AVHRR covers an area of the Earth's surface approximately 1 square kilometer in size; this provides a regional overview of sea surface temperature and its impacts.
In addition to temperature, satellites also provide information about the color of the ocean. This allows scientists to detect the presence of algal blooms, river plumes, and other events. One satellite used for such efforts is the OrbView-2. This satellite is helping researchers to determine the impact of floods along the coast and to detect blooms of harmful algae (dinoflagellates) that can contaminate shellfish and kill other fish and marine mammals.
Satellite imagery is also being used to map features in the water, such as coral reefs. Sensors such as Landsat-7 and IKONOS provide detailed information on local areas. Landsat-7 is part of the Landsat program, one of the longest existing environmental satellite programs. The first Landsat, launched in 1972, had a somewhat coarse resolution of 80 meter pixels. This means that each pixel provided an image of the Earth’s surface measuring 80 sq mi The larger the pixel image, the lower the resolution, which is the level of detail one can make out within the image. While an image depicting 80 sq mi may seem "high-res" when it originates from several hundred miles in space, the next generation satellite, referred to as the “Thematic Mapper,” was launched in 1982 with a resolution of 30 pixel meters. Today, Landsat-7 images are 110 miles square, with 30 pixel meters in color, and 15 pixel meters in black and white. An image of the same area every can be taken every 16 days when the satellite passes over the exact same point on the Earth.
IKONOS is a commercial satellite which can collect very high resolution images of 4 pixel meters in color, and 1 pixel meters in black and white. The imagery it collects is being used to describe reefs, coastal habitats, and similar environments. The Landsat image here depicts Pearl and Hermes Atoll in the Northwest Hawaiian islands. This atoll is part of the Coral Reef Ecosystem Reserve.
Satellites providing environmental imagery are used jointly with other organizations that receive data from various sensors. For example, marine animals, such as sea turtles and manatees, can be fitted with transmitters that relay information about their location. Satellites are becoming a standard tool for studying the oceans.
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