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Thursday, 21 February, 2002, 14:18 GMT
Space: Monitoring the Earth
Graphic, BBC
You quizzed space engineer Derek Todman on the European Space Agency's biggest ever satellite, Envisat, which is set for launch on 1 March.

James Allan in the UK asked: Will the satellite be able to study the impact of human activity on clouds, and shed some light on how big an effect this is having on climate forcing?

Derek Todman replied: As you are probably aware, the impact of human activity on the environment is a very complex affair. There is not only a human impact but nature itself impacts the clouds, namely the seasonal variations.

Envisat will provide a significant amount of data over its lifetime to measure the variation in a number of different aspects of our environment.

The care of the environment does have impacts on other factors of our society

Derek Todman
The scientists will then study the data, correlate the seasonal variations and determine the human effect.

The main instrument on Envisat that will be used for cloud study is MERIS (Medium Resolution Imaging Spectrometer) and this will provide new information concerning for example height, size, and circulation.

This data will pave the way to a better understanding of the effect of human activity on the climate in the longer term.

Matthew Edgley in the UK asked: Do you expect to find a better picture of the Earth than 20 years ago, or have reduced chlorofluorocarbons (CFC) levels and pollutant controls had little effect?

DT replied: It should be remembered that Envisat is not the first European Earth-observation satellite, so that the data is a continuation of the ERS1 and ERS2 measurements and will provide a continuation of the data obtained with instrument improvements based upon previous knowledge.

Earthquake in Azores (Associated Press)
The satellite will give information on natural disasters...
Therefore the observations are improved and a better picture of the interactions will be obtained.

As Envisat is carrying 10 instruments, observations by several instruments at the same time does give improved data when taken together.

Interestingly from data taken on earlier Esa satellites, this has shown that with the reduction in CFC levels, etc. the ozone layer is not deteriorating as rapidly, but the main point is that it takes a long time for nature to recover from an imbalance.

David Hamilton in the UK asked: Could you explain why it took so long to develop Envisat and how much it has cost?

DT replied: The development programme started at the end of 1989 and at that time the objective was to develop a Polar Platform (the "backbone" of the spacecraft) that was capable of meeting many mission scenarios.

The first mission was defined in 1994 and the instrument development commenced at that point. The platform development continued in parallel but the development of the instruments has been the main programme driver, which is not surprising given the complexity of these instruments.

Fires in Indonesia (Associated Press)
...and hotspots caused by forest fires.
Some I consider to be as complex as a small satellite in their own right. Integration and testing of the satellite has also taken a long time.

One of the characteristics of this programme is the time it takes to move the satellite from one site to another, even from one test/integration hall to another.

Also, with so many instruments and interfaces, the integration and test activities have taken a lot longer than originally envisaged.

However, the important point in my view is that they have been tested to the point that we are confident Envisat will work in orbit.

The total price of this mission is 2.3bn euros (1.4bn), which includes not only the cost of the satellite (instruments and platform) but also the launcher and the operating costs for the first five years.

James in the UK asked: Will the satellite's data be incontrovertible? The real question is: will it have any political sway?

DT replied: The actual measurement data is incontrovertible; it will be validated and calibrated by comparing it with data obtained from other sources or known ground references.

Where the discussion takes place is in the analysis of the data and the theories put forward to explain the measurements. With better data and long-term observation, the accuracy of the theory improves and we gain a better understanding.

Personally, I share your view on the question as to whether or not the politicians take note. The care of the environment does have impacts on other factors of our society. In some cases I think governments have taken note and things have changed - CFCs are now not so widely used.

I think on this issue I can only say I hope so and the politicians acknowledge what man is doing, but from my job perspective I can only help build the satellite to help provide the data and tools to see what man is doing to the environment.

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