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Global warming has become one of the biggest problems facing the world,
and averting its possibly catastrophic effects is vital. But to make the
right decisions scientists insist that they need more data-and quickly.

That need has given new impetus to the space community: the obvious
way to collect climate data on a global scale is from remote sensing satellites.
To emphasise this, remote sensing of the environment will be the theme of
International Space Year in 1992.

This month the European Space Agency is due to launch ERS-1, the first
in a new generation of satellites designed to help us to understand the
environment (‘Europe’s orbiting ocean plotter’, ¿ìè¶ÌÊÓƵ, 27 April).
And by the end of the century, ERS-1 will have been replaced by a stream
of new satellites to monitor the Earth’s climate well into the next century.

But remote sensing satellites take years to develop and are very expensive:
ERS-1, including its launch and a ground station in northern Sweden, has
cost £500 million for the ESA member nations who chose to support
the project. With figures many times larger than this earmarked for future
satellites, who should decide on the type of satellites and the instruments
they should carry? Should it be governments with their newfound enthusiasm
for the environment, or should it be the scientists, all of whom have their
own specialist axes to grind.

Space agencies, such as NASA and ESA, are caught in the middle, answerable
to government as their paymasters and scientists as their customers. Researchers
are worried that their voices are not being heard.

The case of ERS-1 illustrates this. John Mason, former director of Britain’s
Meteorological Office, recalls that when ERS-1 was being planned in the
mid 1980s there was very little discussion with the oceanographers about
what instruments it should carry. This observation is backed up by the Coordinating
Committee on Marine Science and Technology, set up in 1988 by the British
government and chaired by Mason.

The committee’s report on oceanographic observation from space, published
in March, concluded that ‘the existing processes of consultation within
the oceanographic community do not allow the total importance or relative
priorities of different users to be assessed, or to be conveyed to BNSC
(the British National Space Centre)’.

ERS-1 has a dual role of providing instant data to meteorological organisations
for forecasting and supplying data at a slower rate for scientists. Britain’s
contribution to the satellite came from the Department of Trade and Industry,
which may help to explain the choice of one of its instruments.

This instrument, the synthetic aperture radar, beams down a powerful
microwave signal towards the surface, detects the reflections and electronically
reconstructs them into a photographic image with a resolution of 25 metres.
The SAR can operate equally well day or night and can see through clouds.

Many oceanographers remain unconvinced that this sort of resolution
is necessary for observing the sea surface. The SAR will probably be used
most for looking at polar ice-useful for both research purposes and to direct
shipping. But its ability to detect ships day or night through heavy cloud
has obvious military applications.

Before the Soviet Union launched its Almaz earth resources satellite
at the end of March, the only other satellite in orbit with a SAR system
was the US spy satellite known as Lacrosse. The British electronics company
Marconi built the SAR for ERS-1. The development of such a complex system
will obviously enhance both its capabilities and prestige as a manufacturer
of radar-a point not lost on the Department of Trade and Industry.

Despite the impressive abilities of remote sensing satellites such as
ERS-1, the predicted changes due to global warming will be so small that
they will not be able to measure them directly.

Climate modellers forecast a rise in the surface temperature of the
planet of less than 0.5 °C per decade. ERS-1’s radiometer, which detects
infrared radiation from the sea surface to measure its temperature, has
an accuracy of about 0.3 °C so during the satellite’s three-year life
it will not be able to detect global warming. Similarly its radar altimeter,
with an accuracy of 10 centimetres, will not be able to detect the predicted
10-centimetre sea level rise per decade.

In the absence of direct measurements, predictions can only be made
by climate models. These can be enormously complex: the Met Office’s climate
model requires 10 ¹² numerical operations to run for a simulated
24 hours. On a powerful Cray supercomputer it takes 10 hours to run just
one annual cycle. Despite their sophistication, predictions for global warming
can vary enormously.

Climate data from satellites will allow modellers to increase the accuracy
of their simulations. The data give an accurate representation of the current
state of the climate which modellers can use as a starting point for their
models. ¿ìè¶ÌÊÓƵs will also learn more about the processes that drive the
climate such as the flow of heat and moisture between the Earth’s surface
and the atmosphere and how wind drives the ocean currents.

The world’s major space agencies are gearing up to provide so much remote
sensing data that it may prove impossible to store it, let alone use it
all . ERS-1 is due to be followed in 1994 by ERS-2 and several other satellites
are planned by NASA and ESA to look at the atmosphere and solid earth. But
the deluge of data will really begin in 1998 when NASA plans to begin its
‘Mission to Planet Earth’.

In 1987 Sally Ride, the America’s first woman astronaut and a scientist
at Stanford University, headed a panel to look at ways of restoring the
America’s leadership in space after the Challenger explosion. The panel
thought up the idea of Mission to Planet Earth which would study the whole
Earth as a system. NASA adopted a version of the plan and its first stage
is a fleet of satellites called the Earth Observing System (EOS).

NASA plans to launch two series of satellites known as polar platforms
because their orbits take them close to the poles. There will be three satellites
in each series and they will be large satellites carrying many instruments.
One satellite from each series will be in orbit at any one time. NASA is
also planning smaller satellites called earth probes for low Earth orbit
and geostationary satellites that sit in high orbits keeping them always
over the same spot on the Earth’s surface.

The EOS project is ambitious and expensive and should provide vast amounts
of data on the environment until at least 2010. But is it really the correct
route to assess the extent of climate change as quickly as possible? Or
is it an attempt to bolster national prestige in space technology?

Paul Morel, director of the World Climate Research Programme, says it
does not completely achieve the former. ‘The scope of the programme is too
small,’ he says. The polar platforms ‘leave open a major gap in our ability
to observe tropical winds’. Also, all the polar platforms are in so-called
sunsynchronous orbits which means that they always pass over the same points
on the Earth at the same time of day. By doing this they are not able to
observe the daily cycles of cloud, radiation and rainfall.

The complexity of the satellites means that the design of the instruments
has to be finalised years before their eventual launches. There is also
an element of putting all the eggs in one basket. ‘They carry a high degree
of risk,’ says John Harries, head of the space science department at the
Rutherford Appleton Laboratory near Oxford. ‘A single launch failure could
set back the programme considerably.’

Small is flexible

ESA’s future plans after the expected demise of ERS-2 in 1997 are far
from certain. Of the ESA member states Britain is almost alone in supporting
a single large polar platform carrying instruments for a multitude of tasks.
The alternative is a series of smaller satellites dedicated to certain disciplines
such as meteorology, climate or oceanography. These would be more flexible
to changing demands for information because they will be quicker to build.
But Britain argues that a single large satellite will be more cost effective.
Britain’s enthusiasm for this option may be partly explained by the fact
that British Aerospace would be the prime contractor for a large European
polar platform.

‘Europe’s policy towards the polar platforms is in disarray,’ says Harries.
At the end of May, the research community will have a chance to have its
say. ESA’s Earth Observation Programme Board is holding a consultative meeting
where its main users of satellite data can state their priorities for future
missions. But researchers are worried that there are other more influential
voices at the ears of the space agency.

‘There is a danger of industry pushing their particular projects without
consulting end users,’ says Roy Gibson, former head of the British National
Space Centre. ‘We must ensure that new instruments and systems are not developed
for their own sake,’ says Harries, ‘but only in response to a clear cut
need for data.’

Later this year the ministers responsible for space of ESA member countries
will meet to approve the agency’s budget. ESA is hoping that the meeting
will make a decision in principle to go ahead with one of two options for
remote sensing. But the decision depends on the funds allocated to the Earth
Observation Programme.

The process for creating research satellites is a curious one, says
Mason. ‘The producers of the hardware and the customers for the data never
quite meet.’ Also, the customers-the scientists-do not provide the money.
Space agencies are generally driven by technology and have their own plans
for what spacecraft and instruments they want to build. They have a habit,
Mason believes, of simply telling users what will be available.

‘There has been too much technology push,’ says Jean-Pierre Contzen,
director general of the European Community’s Joint Research Centre. ‘Perhaps
there should be more market pull.’ Morel believes the space agencies should
have the clear-sightedness to see that the right missions are planned: ‘They
are paid for that purpose.’

But the space agencies are still subject to the whims of national political
priorities. Many researchers believe that powerful independent organisations
are needed to represent those who use the data. In the US, large government
departments often provide the clear demands for data that initiate remote
sensing missions.

The European Environment Agency-which has yet to find a home and start
operations-is still very much an unknown quantity. But there are some European
researchers who hope that this body becomes voice that will be heard by
those who provide space technology.