EUROPEAN SPACE AGENCY NEWS RELEASE
 |
| 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.
|
