Geostationary satellites which are placed in orbit 36,000 km above the equator, moving in the same direction that the Earth is turning, give the impression that they are stationary and remain over its sub-satellite point, the point where an imaginary line joining the satellite and the centre of the Earth intersects with the Earth’s surface. The name for this type of orbit is geostationary or geosynchronous, which means that it continuously views the same portion of the surface of the earth. A large portion of the earth’s surface can be viewed in this manner, and images can be obtained more frequently. Although no sensors of this type are currently in operation, such an instrument could in theory provide high quality observations for a single study area with an image frequency of approximately 30 minutes. The principal applications would be to: determine the effects of storms and tidal mixing on phytoplankton populations, monitor biotic and abiotic material in river plumes and tidal fronts, track hazardous materials (e.g. oil spills and noxious algal blooms). This type of instrument would not provide routine global coverage as is possible from polar-orbiting, sun-synchronous satellites. However, a single imager on a geostationary satellite could provide multiple views during a single day of many locations. The High Resolution Visible and IR Sensor (HiRVIS), which is scheduled to launch in 2008 will be the first ocean-colour sensor on a geostationary satellite.

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