Earth observations
Earth observation satellites are used to monitor the land surface, oceans and atmosphere of our planet, and how all of these change over time. Images of Earth from space are a routine and essential tool in our efforts to manage and protect the Earths resources and environment.
Depending on their mission, Earth observation satellites have different orbits. Weather satellites are placed in high orbits (altitude about 36,000km) above the equator called geostationary orbits, from which they have a constant gaze on the same hemisphere of the Earth. These satellites complete one orbit around the Earth every 24 hours. Other Earth observing satellites are placed in low Earth polar orbits (altitude about 800km) that pass over the poles. These satellites complete one orbit around the Earth every 100 minutes. Because the Earth rotates in the plane of the orbit, such a satellite eventually covers the whole Earth.
Because remote sensing satellites cover the whole globe, they are important for the study of large-scale phenomena like ocean circulation, climate change, desertification and deforestation. They can also be used for a variety of applications such as mapping, urban planning and land use, agriculture, pollution monitoring, coastal monitoring and natural resource management.
Satellites pass over the same areas many times over, making it possible to monitor environmental change caused by human activity and natural processes. Because the data are collected in a consistent manner, satellites can reveal subtle changes that might otherwise remain undetected. Satellites are also important for monitoring remote or dangerous areas that would otherwise remain unobserved. The wellknown ozone hole over Antarctica and the phenomenon of atmospheric ozone depletion was discovered using satellites.
Satellites are often used to provide data rapidly for the monitoring and management of natural disasters such as earthquakes, volcanoes, floods or forest fires, where there may not be enough time to assess damage levels through conventional ground or aerial surveys. Satellites are also used to monitor humanitarian disasters, such as refugee flows from war zones, or for monitoring the spread of water-borne diseases, such as cholera and malaria. Satellite data allow relief organisations to deliver supplies and humanitarian aid rapidly and effectively where they are most needed.
Most satellites are capable of being used for a variety of applications during their life times. All satellite data are archived, providing a valuable data bank for future, unanticipated applications, long after the satellite has ceased to operate. This provides a valuable return on the cost of building and launching the satellite. In South Africa, the CSIR Satellite Applications Centre maintains an archive of images taken by a variety of satellites dating back to 1972. This archive is a national resource.
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Hubble directly observes Planet Orbiting Fomalhaut.
