Paris

Preparations for the launch on 1 March of Envisat, the Earth-observation satellite developed by the European Space Agency (ESA) at a cost of 2.3 billion euros (US$2.0 billion), are reaching their final stages in Kourou, French Guiana.

Envisat's unusually large number of instruments will provide integrated data about the Earth. Credit: A. VAN DER GEEST/ESA

Envisat weighs 8,300 kg and carries 10 different instruments — an usually large number for an individual satellite. Data from the satellite will find a wide range of uses, from the development of climate models to the calibration of greenhouse-gas emission targets.

The launch was put back from last October after problems with the upper stages of the Ariane 5 launch rocket led to another ESA satellite, Artemis, being placed in the wrong orbit (see Nature 412, 368; 2001). The rocket's developers — Arianespace, based in Evry, south of Paris — say they have now corrected the problem, which was caused by frozen water blocking the fuel-injection system.

Sensors on board Envisat will measure parameters such as sea level and temperature, and the spectrum of the solar radiation reflected by the Earth. Existing satellites capture some similar data, but Envisat will allow them to be studied simultaneously. It will also provide new data, such as measurements of trace atmospheric gases. “Combined measurements are the key to understanding phenomena like El Niño,” says José Achache, head of ESA's Earth-observation programme.

Envisat also carries a sensor for measuring ocean chlorophyll and terrestrial biomass, which will improve measurements of plant productivity. Such data will help to determine greenhouse-gas emission targets by providing accurate measurements of the amount of carbon absorbed by oceans and by large areas of vegetation, such as the boreal forests of Europe and Asia.

Over 700 groups of scientists, including 150 from the United States, have already been given clearance by ESA to work with the data, much of which will be made available over the Internet. But some at the agency say that in the future there may not be enough trained researchers and resources to make the most of the huge amount of data Envisat will provide. “Now Envisat is here, the biggest challenge for Europe's funding agencies is to make sure it can be properly exploited,” says David Southwood, director of science at ESA.

Despite Envisat's wide range of applications, ESA is unlikely to launch another satellite of its size. Future European Earth-observation missions will use smaller satellites, tailored in part to meet the needs of a new plan by ESA and the European Commission to create a global network of satellites to provide data on security issues and the environment (see Nature 414, 140; 2001).

→ http://envisat.esa.int