Between the Atlantic Ocean and the mangrove swamps, in the hi-tech surroundings of Europe's spaceport, a spacecraft is undergoing final checks.

After more than 10 years in development, Europe's 2.3bn-euro mission to assess the environmental health of the planet is about to launch.

How Envisat looks now

To mark the occasion, scientists and journalists are being given the chance to see the Earth-observation satellite - it is called Envisat - up close in the clean room.

In a decontamination area, we don gowns, hats and overshoes. Cleanliness is paramount as even a single human hair could stop an instrument working in space.

One-by-one, we pass through an air-lock into the giant, sterile, hanger, where two technicians are gently swabbing the spacecraft's silver panels.

Climate questions

They are putting the finishing touches to the largest Earth-observation satellite ever built in Europe. Take-off is set for the early hours of 1 March.

The 14-year-programme has been quite an adventure, says Derek Todman, project manager for the "backbone" of the satellite, which was built in the UK under contract to the European Space Agency.

Getting ready to enter the clean room

"The objective is that we can understand a lot better what mankind is doing to the environment," he told BBC News Online.

"Hopefully, we can then put in the necessary measures to stop mankind continually polluting the environment."

When Envisat is in space, with its solar array unfurled, it will span the length of a tennis court.

The spacecraft will orbit the Earth 14 times a day for the next five years or more, monitoring for climate change and environmental pollution.

Disaster warning

Its 10 scientific instruments will build up a detailed profile of the planet's atmosphere, oceans, land and polar ice caps.

Images taken by the satellite could even help after natural disasters such as volcanic eruptions, earthquakes and floods, by giving valuable information about a disaster scene.

How Envisat will look in space

According to Paolo Pasquali of Sarmap in Switzerland, this data might even prove useful in predicting volcanic eruptions, such as the recent disaster in eastern Democratic Republic of Congo at Mount Nyiragongo.

"We need repeated observation of the ground and we need to monitor all of the small movements of the Earth for long periods," he told BBC News Online.

"The importance of this work is to couple these kinds of measurements with the work of people like seismologists and geologists that have access to this data and can use their models to forecast events."

Ocean events

Envisat could also shed light on the detailed mechanisms that lie behind El Ni�o, the climate event that sees the wet conditions normally found in the western Pacific move to the east, and the arid conditions common in the east appear in the west.

Duncan Wingham, Professor of Climate Physics at University College London, UK, says the satellite could give accurate predictions of whether the Pacific Ocean is going into an El Ni�o phase six months or even a year in advance.

The craft will launch on an Ariane 5

"In the tropics and the mid-latitudes, the measurements provided by Envisat give us a very good handle on predicting those parts of the ocean," he says.

Envisat will be launched on the giant Ariane 5 rocket, which can carry much heavier payloads than its predecessor, the Ariane 4.

But the new rocket blew up on its maiden flight in 1996, shattering the hopes of hundreds of space scientists who saw its precious cargo, four cluster spacecraft, go up in smoke.

There have been several successes since then, but another Ariane 5 launch in July last year placed two satellites into the wrong orbit, leading to further delays for the Envisat mission, then scheduled for Autumn 2001.

Bitter-sweet farewell

Now, Envisat has a new deadline, and there is much left to do.

"It's very easy for me to say that all we have to do now is a little bit of electrical testing, put the fuel in it, bolt it to the top of the rocket and launch it," says Derek Todman.

"In fact, that represents a lot of hard work for my team to complete the final integration and assembly ready for launch."

When Envisat was shipped to French Guiana, it took a Russian Antonov transport plane, two Boeing 747s and a boat to move 300 tonnes of equipment.

Derek Todman says the only way now to get the spacecraft out of Kourou is on an Ariane. But the lift-off will be bitter-sweet.

"I think I'll feel extremely happy once it's up there, it's pointing to Earth, the solar array is out and it's successful," he says.

"The other side of that is having spent a long time on a project and it's then launched, your job is finished so there'll be a little bit of sadness.

"It's going to be very strange to get up in the morning and think: 'well, the satellite's gone, now what?'"