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EUROPEAN SPACE AGENCY NEWS RELEASE
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| Illustration of Envisat in Earth orbit. Photo:
ESA |
In July
an Ariane 5 launcher will send into orbit Europe's big new
environmental satellite, Envisat. Scientists will expect
fresh insights from its data, into how the world is changing.
The 8-tonne spacecraft will continue and extend the work
of ESA's ERS-1 and ERS-2, which since 1991
have established a distinctive role in watching global change,
notably in the world's oceans and ice sheets.
An important ozone monitor was added on ERS-2. One of the
new instruments on Envisat will observe the variations in
ocean colour due to the seasonal blooming of life, which
plays a big but poorly understood part in controlling the
amount of carbon dioxide in the atmosphere. Improved instruments
for gauging ozone and other trace gases are also on board.
Yet Envisat is just the flagship of a fleet of satellites
being built in Europe to make better sense of the possibly
adverse climate trends on the planet that is our only home
in the desert of space.
While everyone wonders about unusual weather and what it
may mean for the future, spacecraft are the world's chief
eyes on current weather and climate variations. Surface
stations are scattered very unevenly around the globe. They
are especially scarce in polar, oceanic and sparsely inhabited
land regions where, some climate forecasters suggest, the
greatest changes may be occurring. Only satellites can observe
the weather and associated climatic and environmental changes
comprehensively and objectively, day by day and decade by
decade. So several ESA programmes converge on the issues
of climate change.
On behalf of EUMETSAT, ESA is developing two advanced satellites
for routine weather observations. One is Meteosat Second
Generation (MSG) to replace the Meteosat series that, since
1977, have watched the weather over Europe, Africa and adjacent
regions and ocean from a geostationary vantage point. Besides
its familiar use in daily weather forecasting, Meteosat
provides a huge archive for climate studies, for example
in helping to reveal changes in the Earth's cloud cover
from year to year. MSG-1 is scheduled for launch in 2002.
It will generate sharper images twice as often, and with
twelve wavelength channels rather than the three in the
current Meteosat. It will also carry the Geostationary Earth
Radiation Budget experiment to monitor the difference between
reflected sunlight and the infrared rays emitted from the
upper atmosphere, which are partially blocked by greenhouse
gases.
From 2005 the first Metop satellite will orbit over the
poles. In a cooperative programme between EUMETSAT and ESA,
Metop is the space segment of the EUMETSAT Polar System.
This in turn is part of a joint European-US satellite system
coordinated with the US National Oceanic and Atmospheric
Administration. The European and American satellites will
share some basic instruments, including an Advanced Microwave
Sounding Unit to measure the temperature of the air at many
levels in the atmosphere. A puzzle about climate change
is that the rising global temperatures inferred from surface
stations are not matched by any long-term warming of the
lower atmosphere. Additional European instruments on Metop
will improve atmospheric soundings, and measure atmospheric
ozone and near-surface winds over the ocean.
ESA's Earth Explorer programme aims to advance earth science
and the techniques of observation from space, beyond the
present capabilities of current generation of Earth Observation
satellites. The first core mission of this programme is
GOCE (Gravity and Steady-State Ocean Circulation Mission)
due for launch in 2004/5. It will measure regional variations
in the Earth's gravity more accurately than ever before.
One of its benefits will be a better understanding of the
ocean currents, which play a major role in the climate by
transporting huge amounts of heat between different regions.
The second Earth Explorer core mission will be ADM (Atmospheric
Dynamics Mission, 2004/5). It aims to fill a big gap in
observations of the winds of the world. The computer models
that calculate daily weather forecasts and make climate
predictions, have to diagnose and predict the winds at all
levels in the atmosphere. Observations that might check
whether the reckonings are correct are limited to those
relatively few places where radiosonde weather balloons
are flown routinely. Coverage of the oceans and the Southern
Hemisphere is especially sparse. ADM will use an ultraviolet
laser beam to measure wind speeds at 20 levels in the air,
by detecting echoes from molecules and dust particles carried
by the winds.
In addition to its core projects, ESA's Earth Explorer programme
supports smaller "opportunity" missions. Cryosat (2003/4)
will find out whether the great ice sheets of Antarctica
and Greenland are melting as a result of global warming.
It will also clarify the role of sea ice in climate variations.
ERS-1 and ERS-2 have measured year-by-year variations in
the thickness of the ice sheets with a radar altimeter,
but have detected little change overall. This may be because
the radar averages the ice altitudes across wide areas.
To look for significant melting at the edges of the ice
sheets, Cryosat will use twin radars to detect changes across
areas just 250 metres wide.
Soil moisture and ocean salinity are the targets for SMOS,
the second "opportunity" project. Life on land relies almost
entirely on the thin layer of moisture in the soil that
supplies the roots of plants, and any global or regional
trends due to greater or lesser rainfall would be one of
the most important indicators of climate change. SMOS (2005/6)
will use a multi-beam radio telescope to detect 21-centimetre
radiation from the land surface, the intensity of which
is a good indicator of soil moisture. The same radiation
coming from the ocean will reveal the salt content of the
sea surface, which has a major influence on ocean currents
and hence on the climate.
The role of the Sun as a natural agent of climate change
is investigated by ESA's Space Science Programme. Intense
magnetic activity on the Sun seems linked to warming effects
on the Earth, but the solar mood varies from decade to decade
and century to century. When the ESA-NASA Ulysses spacecraft
first flew over the solar poles in 1994-95, it showed that
the magnetic field far from the Sun is much more uniform
that experts expected. As a result, scientists were able
to deduce, from magnetic records on the Earth, that the
interplanetary magnetic field doubled in strength during
the 20th Century, probably with related contributions to
global warming.
The ESA-NASA SOHO spacecraft, stationed 1.5 million kilometres
out on the sunward side of the Earth, has monitored changes
in the Sun since 1996. It measured an expected increase
in the intensity of sunlight while the Sun approached its
present maximum of magnetic activity, as indicated by a
rising count of sunspots. SOHO has also discovered an ever-varying
dynamo deep beneath the surface that seems to be responsible
for the Sun's outward show of magnetism.
When the Sun's role in the Earth's climate changes is better
defined, anticipating its mood will be important for forecasting.
Some experts think that the best predictor of the intensity
of solar activity is the strength of the magnetic field
at the Sun's poles, but this is hard to gauge. ESA's successor
to SOHO will be the Solar Orbiter, due for launch around
2010. For one month in every five, the Solar Orbiter will
swoop close to the Sun and observe its stormy atmosphere
in far greater detail than ever before. It will also use
encounters with the planet Venus to slant its orbit and
achieve a better view of the Sun's poles and the magnetism
there.
ESA is now examining a selection of five proposals for further
core missions in the Earth Explorer programme. These would
investigate atmospheric chemistry, clouds and aerosols,
ecological changes, or water vapour in the atmosphere. The
exuberance of the proposals, backed by dozens of scientists
from ESA's member states and other countries, is a sure
sign that many new possibilities remain for learning more
about our planet from space. By 2015, when the Solar Orbiter
will be helping scientists to forecast the Sun's activity
for the following decade, scientific understanding of both
manmade and natural climate change should be far deeper
than it is now - thanks at least in part to Europe's climate-tracking
spacecraft.
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