Green eye in the sky

A voyage into space for a three-dimensional monitoring of the polluted environment

Published: Sunday 31 March 2002

ENVISAT ready to embark on ‘Mission Environment -watchFOR three minutes, the night sky lit up on March 1, 2002, at the European Space Agency (ESA) launch centre at Kourou in French Guiana on the northern coast of South America. It was from here that an Ariane-5 rocket blasted off and put into orbit ENVISAT— the largest and most expensive satellite ever built in Western Europe. And with this development, a new chapter in the monitoring of the world’s environment was scripted. Carrying 10 unique instruments falling into three categories (see box: Fully loaded satellite), the 8.5-tonne, 25-metre-high ENVISAT is as big as a double- decker bus. Satellites of ENVISAT’s size are unlikely to be launched again. “It’s the last of the dinosaurs,” says one UK digital sensing expert. The flying behemoth will revolve around the earth every 100 minutes and will provide unprecedented data on the health of the sick earth. Apart from studying other things, the satellite will sense the warmth of the oceans, the height of the waves, count plankton, measure algae, map rainforests and grassland, gauge snow and ice cover and garner information on greenhouse gases, global warming and the status of ozone layer. It will give a comparative picture of all the interactive elements which will assist political decision-making on climate change. “ENVISAT will be the first satellite to contribute to monitoring of compliance of the Kyoto Protocol,” says Harmut Grassl, former director of the World Climate Research Programme. Scientist John Burrows of University of Bremen concurs and feels that the satellite is “an effective instrument for monitoring the Montreal and Kyoto treaties”. The total cost of the ENVISAT programme is US $2 billion, distributed over 15 years. ENVISAT represents not just huge investments but years of painstaking research and preparation by 14 different countries — the 13 members of the ESA and Canada — as well. The satellite has been built by a 50-company team including British firm Astrium, which was lead contractor for the satellite superstructure. It is designed to operate in a sun-synchronous orbit for five years. Although there were glitches hours before take-off, in the end it was all’s well that ends well for the manufacturers and the scientists involved in the project. The successful launch of ENVISAT not only re-establishes the reliability of the Ariane- 5 rocket, it is also a comeback of sorts because in June 1996 the rocket’s maiden test met with failure and exploded 37 seconds after lift-off. The result: four uninsured scientific satellites worth US $500 million crashed into mangrove swamps. 

Fully loaded satellite ENVISAT will give a comprehensive picture of the state of Earth’s health

ENVISAT carries 10 instruments, each dedicated to different environmental criteria. These devices will study the Earth’s surface, scrutinise the atmosphere and monitor the satellite’s position relative to the ground. The instruments have been divided into three categories: Surface: The Earth’s surface will be monitored by the largest instrument of the satellite, the Advanced Synthetic Aperture Radar (ASAR), the Medium Resolution Imaging Spectrometer Instrument (MERIS) and the Advanced Along Track Scanning Radiometer (AATSR). ASAR will be used to monitor ocean wave characteristics, while MERIS will help in determining the level of carbon monoxide in the oceans. Atmosphere: The Michelson Interferometer for Passive Atmsphere Sounding (MIPAS), the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) and the Global Ozone Monitoring by Occulation of Stars (GOMOS) will keep tabs on the Earth’s atmosphere. SCIAMACHY will make the first attempt to study carbon dioxide levels from space. GOMOS will measure the distribution of ozone within the Earth’s upper atmosphere by recording how this gas affects light from the stars. Altimetry: To monitor the position of ENVISAT relative to the ground, the Radar Altimeter 2 (RA-2), the Microwave Radiometer (MWR), the Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) and the Laser Retroreflector (LRR) will be used. MWR can detect changes in levels of water in clouds.

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