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Envisat: An Eye on Earth, See, and Sky

Press Release From: French Advances in Science and Technology
Posted: Wednesday, March 6, 2002

Any old earth-observing satellite could have recorded a very high tension area over the Ariane launch site in French Guyana last Thursday night as Arianespace's Ariane 5 heavy-lift launcher put Envisat, the European Space Agency's 8-ton multi-instrument platform, into orbit, while a lot of breath was held.

First of all, the future of the Ariane program after a spotty history of heavy-load launching was at stake; secondly, the ESA had a huge number of eggs in one $2-billion-basket in what will likely prove to be the last of the big cluster platforms; not to mention the hundreds of scientists and laboratories who had 10-15 years invested in the instruments and projects waiting to be borne aloft.

In a big boost for European space, and very likely a small one for the champagne market, Envisat was placed in orbit with eye-popping precision, arriving without a glitch onto a sun-synchronous orbit about 20 meters from the planned path, and with so little maneuvering necessary that its unspent fuel reserve may mean a much-extended life.

Envisat is an ambitious program of earth observation to be carried out by 10 on-board instruments, and fina?Ó¯/ by 14 European nations. As explained by the ESA's Director of Earth Observation, Josˇ Achache (also chair of the international Committee on Earth Observing Satellites-CEOS), Envisat will be focusing its sharp eyes on three large areas: the atmosphere, the oceans and polar caps, and land.

Four of its instruments will keep Envisat's data as accurate as possible by providing constant data on its position and speed, one of which--the altimeter--will also provide data on ocean level and even the topography of the ocean floor. Three will concentrate on tracking not only the concentrations but also precise locations of a number of atmospheric components and pollutants, including greenhouse gases, ozone, aerosols of all origins, industrial pollution, and even the effects on the atmosphere of forest fires, dust storms, and volcanic eruptions.

One of these, GOMOS, is designed to provide ozone-concentration data by star occultation, whereby the spectra from bright stars will be analyzed as Envisat orbits the earth and light from the stars passes through the atmosphere at the horizon, thus identifying the chemical makeup of that patch of atmosphere.

An ocean-gazing spectrometer will pick up changes in ocean color due to algae proliferation, while a radiometer reading several wavelengths of light is designed to provide a detailed map of ocean temperature (and will even be able to detect a forest fire getting started). Polar ice will also be under close surveillance, as will icebergs, and even dishonest tankers illegally rinsing their tanks at sea.

Radar on board this global-scale Big Brother will also detect slight changes in the land levels, such as Venice slipping a few millimeters into the sea or Djakarta sinking slightly as water tables are over-solicited. Achache promised that a very liberal policy of access will be observed, predicting that probably a 100,000 scientists worldwide will benefit from Envisat data. He says the ESA is ready for data demand, as a result of having invested in considerable crunching power in anticipation of the huge flow of data Envisat will be beaming down.

First though, a several month period of synchronization and calibration is required to ensure reliability. Meanwhile, European space, at national as well as multilateral levels, is tending to the preparation of the next generation of earth observers which will be small, specialized satellites requiring much less breath to be held at launch time and presumably adding years to launch directors' lifespans.

(Le Monde, February 27, p28, Pierre Barthˇlˇmy; Libˇration, March 2, p18-19, Sylvestre Huet; Le Figaro, March 2, p11, Fabrice Nodˇ-Langlois)

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