Information>Satellites

Satellite missions

Polar orbiting or geostationnary earth observation missions are vital for operational applications (meteorology, environment monitoring, ocean circulation forecast,...) and long-term survey of the climate and the ocean. They provide global observations on a regular and consistent basis for numerous geophysical or biogeochemical parameters over the ocean, including surface winds, waves, heat content, sea level, sea surface temperature, sea ice, air/sea fluxes,...The retrieval of this information is performed through a wide range of onboard instruments including active and passive sensors operating in various wave length. This section provides an overview of the various missions and their benefits to ocean knowledge.

Originally intended as a processing center for the ERS-1 & ERS-2 satellites, the CERSAT has been archiving and distributing - since 1996 - data from other satellite missions. By integrating new sensors (scatterometers, radiometers, altimeters,...) in its database, the CERSAT is preparing the after-ERS era and can act as a valuable node in the forthcoming earth observation networks. Merging various sensors, it is also able to generate multi-sensor value-added products.

Polar orbiting satellites

The orbits of these satellites carries them within a few degrees of the Earth's poles, and they complete around 15 orbits a day (approximately one every 100 minutes). The satellite measures a swath of the earth's surface below it as it travels. Due to the relatively low orbit of these satellites, data is usually of high spatial resolution.

However, the temporal resolution of these satellites is dependent on their orbit and sensor characteristics. Satellites such as Envisat have a 35 day repeat cycle - the time taken to re-visit the same spot above the earth's surface. The time taken to make a repeat measurement at a point on the earth's surface may be significantly reduced if the instrument has a wide swath width, or the point is at high latitude, where the orbit tracks are closer together.

Geostationary satellites

The orbit of geostationary satellites is much higher - around 36,000 km. The satellite is positioned directly above the equator, and its speed is presicely matched the the speed of rotation of the Earth. The result is that the satellite stays in the same location relative to the earth's surface. The satellite can continuously monitor a large area, and a few well placed satellites can cover a large part of the earth's surface. The major disadvantages are that higher latitudes are not well observed, and the higher orbit leads to lower spatial resolution.