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TTHE economic summit in Paris earlier this month, the leaders of the
seven richest industrialised democracies did something unprecedented. They
devoted a third of their final communique to the environment. The leaders
urged all countries, ‘to give further impetus to scientific research on
environmental issues’, and to combine their efforts to improve observations
and monitoring on a global scale.

President Bush repeated his commitment to dealing with international
environmental problems last Thursday in his speech to commemorate the 20th
anniversary of the first landing on the Moon (see This Week). Calling for
a major national and international effort to study the environment, he said
that this anniversary reminded us of what the astronauts saw during their
trip: ‘The Earth, blue and fragile, rising above the Sea of Tranquillity.’

The aim is to produce mathematical models that describe the interacting
processes on Earth and can predict accurately what is going to happen to
our planet. Prodded into life by threats such as global warming and the
ozone hole, a plethora of international and national efforts to monitor
the Earth’s processes on a planetary scale exist already.

The organisations working on this include the International Geosphere
and Biosphere Programme, set up by the International Council of Scientific
Unions in 1986. The IGPB, in turn, has interests in common with the World
Climate Research Programme, sponsored by the UN Environment Programme, the
World Meteorological Organization and the International Oceanographic Commission.

Each organisation has spawned numerous other programmes, each examining
an aspect of the Earth’s behaviour and all in need of money. They also need
data. In the US, and increasingly, internationally, gathering the information
needed to build the mathematical models is becoming known as ‘Mission to
Planet Earth’.

The detailed definition of this phrase depends on who uses it. In the
broadest sense, a Mission to Planet Earth would involve instruments on satellites
in different orbits, on land, on aircraft, in balloons and at sea. These
instruments would monitor the processes going on in the Earth’s inner core,
oceans, biosphere and atmosphere and the interactions among those systems
(see Box opposite).

This undertaking must have a strong interdisciplinary flavour, and must
include atmospheric chemists, geophysicists, ecologists and many of the
other ‘ists’ that spring to mind. Don Anderson, president of the American
Geophysical Union, told a congressional committee in March: ‘You cannot
isolate the atmosphere, the oceans and the crust. These systems interact
and are affected by the magnetic field that is generated by the core.’

The phrase ‘Mission to Planet Earth’ became popular in 1987 when Sally
Ride, the US’s first woman astronaut and a scientist at Stanford University
in California, headed a study for NASA. Mission to Planet Earth was one
option her group looked at to restore the US’s leadership in space after
the Challenger disaster. NASA has now adopted its own version of the mission
and plans to ask Congress for money to begin the first stage – the Earth
Observing System.

If approved, the EOS will be the major new start for the agency’s Office
of Space Science and Applications (OSSA) next year. NASA needs $200 million
in the first year of the project. The first part of the EOS would be launched
in 1996. If the full plan goes ahead, the EOS will need about $1500 million
a year from 1994.

Such a high level of funding would leave very little of the OSSA’s share
of NASA’s budget for other projects, such as planetary science. So, if the
agency is to implement the full plans for the mission, or even for the EOS,
the US would have to adopt the project as a national goal in much the same
way as it did the Apollo programme.

Financial burden

Despite the financial burden of Mission to Planet Earth, the National
Research Council in the US endorsed its aims in a report published last
year on the principal scientific issues in space science from 1995 to 2015.
Anderson served on the board preparing the report, working with geophysicists,
meteorologists, oceanographers, chemists and space physicists from universities
and government research laboratories. He told Congress in March: ‘Although
the members of the group have many different interests, priorities and allegiances,
they agreed not only on the necessity but also on the strategy of an ambitious
Mission to Planet Earth.’ The council defines the mission even more broadly
than NASA.

The EOS will include two series of platforms. Known as polar platforms,
these will be in orbits that pass near to the poles. Every three to five
days, the platforms will pass over the same spot on the Earth. The orbits
will be Sun synchronous, in other words, the angle of incident radiation
falling on the Earth from the Sun will be the same for a given spot each
time the platform passes overhead. As a result, scientists will not have
to correct the data they receive to eliminate changes caused by the radiation
hitting a particular spot at a different angle.

Each series will have three polar platforms. The platforms will be designed
to last for five years, and will fly consecutively, providing scientists
with data for 15 years in succession. The plan is to have two platforms,
one from each series, in orbit at any one time. Wes Huntress, an assistant
to the OSSA’s director, says that NASA has enough in its projected budget
to pay for the series-A platforms and their instruments. But series B would
require more money from Congress.

Huntress says that his office is still working out details of the costs.
If they fly, the series-B platforms will study the chemical composition
of the upper atmosphere and winds in the stratosphere, and possibly carry
an instrument to study plate tectonics.

The platforms in series A will carry instruments to detect radiation
from the Earth in the visible, infrared and microwave parts of the electromagnetic
spectrum. Different instruments on the platforms will be able to resolve
features ranging from 1 kilometre to 30 metres in size. They will collect
data about land, oceans and cryosphere. (The cryosphere includes the ice
caps, snow cover on mountains and seasonal deposits of snow.) The visible
wavelengths will provide a picture of the extent of, for example, tropical
rainforests. Infrared radiation can monitor, for example, the health of
crops or lava flows during volcanic eruptions. David Pieri, from NASA’s
Jet Propulsion Laboratory, told delegates at the International Geological
Conference in Washington DC last week that lava flows are basic to the understanding
of eruption energetics, but without infrared data from remote-sensing satellites,
‘we have no handle on the problem’. Pieri says that only two infrared instruments
on the world’s remote-sensing satellites now operate at the wavelengths
needed to study lava flows.

Some instruments on the series-A platforms will also measure atmospheric
characteristics, such as temperature, humidity and dust content. While these
readings are important scientifically in their own right, they are also
crucial to the whole EOS project, because all of the radiation emanating
from the Earth is scattered and absorbed to some extent by the atmosphere
before it reaches the satellite. With direct measurements of the atmosphere,
scientists will be able to develop the algorithms they need to process the
spectra recorded at the satellite so that they are a true representation
of the radiation coming from Earth.

Ted Maxwell, from the Smithsonian Institution, who was recently appointed
to NASA’s planetary science programme, says that the ability to correct
data for atmospheric effects was one of the bullets that applicants to the
programme had to bite. Maxwell was one of 200 scientists who reviewed proposals
to participate in the EOS. The reviewers selected 55 teams, each working
with different instruments that NASA is paying for. The teams, announced
in February, include more than 500 scientists from the US and 13 other countries.

The scientists had to show how they would process data and make it available
to the scientific community within a few days. Sharing data at such an early
stage is not common practice. ¿ìè¶ÌÊÓƵs usually have exclusive rights to
the data collected by the instrument they are working with. They then have
time to work on the data and publish their findings.

Some of the teams will work with data collected by more than one instrument.
For example, one team of scientists from universities in Australia will
study the relationship between climate, ocean circulation, biological processes
and marine resources in Australasia. In addition, atmospheric scientists
will be needed to help to ensure that the data recorded by instruments are
a true representation of the radiation emanating from Earth.

If the US takes a bold approach to Mission to Planet Earth, the EOS
might stretch to the third series of platforms, carrying synthetic aperture
radars. Instead of passively detecting radiation from the Earth’s surface,
these instruments would beam microwaves at the surface and detect them on
their return. The differences in the physical characteristics of the incident
and reflected radiation give information about, say, the direction of ocean
currents and the height of waves.

Conventional radar receives signals along the length of an aerial and
combines the signal to produce an image. To resolve, say, an object 25 metres
across, a radar at an altitude of several hundred kilometres would need
an aerial 2 kilometres long. A synthetic aperture radar with this resolution
needs an aerial only 10 metres long. It ‘synthesises’ a much larger aerial
by receiving signals continuously through 2 kilometres of orbit, then combining
the signals electronically.

At the same time as requesting money for the EOS, NASA will ask Congress
to fund a second, cheaper element of Mission to Planet Earth – a series
of small satellites known as Earth probes. These will complement the polar
platforms, because they will be in low orbits passing over the equator.
Satellites at such altitudes orbit the Earth in 90 minutes and can take
readings more often.

The polar platforms will pass over the same spot only once every three
to five days (depending on the final design). So the Earth probes can monitor
processes that the polar platforms cannot. For example, says Huntress, satellites
in equatorial orbit could monitor tropical rainfall, which varies strongly
from one time of day to another.

The third type of satellite in the Mission to Planet Earth would be
in geosynchronous orbit, 36 000 kilometres above the equator. At this altitude,
satellites orbit at the same velocity as the Earth rotates, and stay in
the same position with respect to a point on the surface. This means that
they can continuously measure a process on the Earth.

Because geosynchronous satellites are in far higher orbits than the
polar platforms or Earth probes, NASA will have to develop more sophisticated
instruments to record information from thousands of kilometres. In particular,
NASA would have to develop accurate pointing systems to home in on a spot
36 000 kilometres away.

Geosynchronous satellites are widely used for communications. Huntress
says that plans for geosynchronous observation satellites are five years
behind plans for the polar platforms.

The agency also needs to develop computers to process and store the
huge amounts of data the satellites will collect. The polar platforms, for
example, will bombard the Earth with a million billion bytes of data per
day. No matter how sophisticated the storage and processing, that amount
of data will be unmanageable. Current studies are determining how much of
the data needs to be stored.

Although NASA, as an agency with an annual budget of billions of dollars
(this year Congress is expected to allocate it between $12 billion and $13
billion), is an important provider of instruments to gather remote-sensing
data, other agencies play their part. The European Space Agency and Japan’s
space agency will each contribute a polar platform to the US’s international
space station programme.

The world’s agencies all have remote-sensing programmes, but these are
not coordinated. The International Space Year in 1992, though, may provide
a focus. An initiative by the US, the ISY is a successor to the International
Geophysical Year in 1957, which started the space race. The world’s space
agencies have formed a forum, chaired by Hubert Curien, the French Minister
for Research, to plan for the ISY, and have adopted Mission to Planet Earth
as a theme. But the ISY has its own interpretation of the mission.

Between now and 1992, the agencies do not have time to develop a new
space mission. So the ISY defines Mission to Planet Earth as producing global
standards for observing systems, establishing data formats to facilitate
the exchange of information between different programmes, improving the
algorithms for transforming raw data from satellites into information that
represents what is happening on Earth and establishing a common archive
for remote-sensing data.

It all comes down to the quality of the data

SCIENTISTS rely on data from remote sensing and from instruments on
the ground to provide information about the processes under way within and
above the Earth. Aircraft, balloons and satellites carry the instruments
that gather data. Satellites, however, are the only way to make global observations
in a short time.

Every material on Earth reflects, transmits or absorbs electromagnetic
radiation in a characteristic way which gives it a spectral signature. From
that signature, scientists can deduce information about a particular area.

The visible wavelengths can provide information for maps, details of
infrared radiation can tell us about the health of crops, ratios of infrared
to red light can give information about the type of ore in the ground. With
the development of synthetic aperture radar, microwaves beamed from a satellite
can yield information about the direction of ocean currents or the height
of waves.

Remote-sensing from satellites, though, is in its infancy. ¿ìè¶ÌÊÓƵs
have a lot to do to establish just what they can deduce about what is happening
on Earth from spectra recorded by satellites. Aircraft and balloons are
much closer to the source of their observations, and it is easier to validate
the data they collect than the data satellites record.