For its second cycle of the Earth Explorer Opportunity Missions, ESA has
recently selected three proposals to enter feasibility study: ACE+ , an
Atmosphere and Climate-Explorer; EGPM, the European contribution to Global
Precipitation Mission, and SWARM, a constellation of small satellites to
study the dynamics of the Earth’s magnetic field and its interactions with
the Earth system.

Following a call for proposals in June 2001, ESA received 27 responses,
which encompassed all science and application oriented disciplines of
Earth Observation remote sensing. In January 2002, 25 were submitted for
evaluation to scientific Peer Teams for an in-depth scientific and
engineering review. The review was then analysed by the Earth Science
Advisory Committee (ESAC) which established a shortlist of six missions.
Finally, on May 15-16, ESA’s Programme Board for Earth-Observation
selected three missions to undergo feasibility study.

The first Earth Explorer Opportunity Mission selection took place in 1999
and resulted in the selection of Cryosat and SMOS. Cryosat, to be launched
in 2004, will study ice sheets and sea ice, while SMOS, scheduled for
launch in 2006, will measure soil moisture and ocean salinity. The first
Earth Explorer Core Mission selection of 1999, saw the birth of the
Earth Gravity field and Ocean Circulation (GOCE) mission and the
Atmospheric Dynamics Mission (ADM-Aeolus) to be launched in 2005 and 2007

Unlike the larger Earth Explorer Core Missions, which are ESA-led research
missions, Opportunity Missions are smaller, have a larger degree of
industrial implication and are not necessarily ESA-led. Their
cost-to-completion ranges in the order of 110 Meuro.

The three candidate opportunity missions recently selected will complement
areas of research currently under development in the Earth Explorer
programme. Once the feasibility studies are complete, two of the three
missions will be retained for implementation, with the launch of the
first envisaged for 2008.


The principal goal of ACE+ is to measure variations and changes in global
atmospheric temperature and water vapour distribution and so provide
valuable data for monitoring climate change. ACE+ will also be used to
improve weather forecasting. The mission will use four satellites in
orbits between 650 and 850 km altitude. Each will carry an L band
receiver for GPS/Galileo sounding and a multi-frequency X-K band
transmitter or receiver for satellite-to-satellite cross-link

The areal coverage of the mission must be such that the profiles are
globally and homogeneously distributed. The proposed constellation of 4
satellites will produce around 7000 humidity and temperature soundings per
month, which will be appropriate for use in climate monitoring.
Approximately 5000 refractivity soundings per day from GPS/Galileo radio
occultations will also be produced and will be assimilated into weather
forecasting systems.


This mission is a major European contribution to the Global Precipitation
Mission (GPM), which is an international initiative to ensure the delivery
of global precipitation fields 8 times per day. GPM is based on a
satellite constellation and is the successor of the NASA/NASDA Tropical
Rainfall Measuring Mission (TRMM).

Since availability of fresh water is so vital for life on Earth and human
development, the scientific reasons and the justification for a
precipitation-measuring mission are self-evident. Almost all aspects of
meteorology, climate studies, hydrology, economy and society are directly
influenced by the presence or absence of precipitation.

EGPM is a mission consisting of a single satellite in a sun-synchronous
low Earth orbit and carries a precipitation microwave radiometer, which
will provide global rainfall observations. It is an element of the joint
NASA-NASDA GPM mission proposal, which comprises a ‘core’ satellite,
carrying a precipitation radar and a precipitation radiometer, and a
number of smaller satellites with only a precipitation radiometer on each.

EGPM extends the proposed GPM mission by providing data that are needed at
high latitudes (such as Europe and Canada).


The objective of the SWARM mission is to provide the best survey ever of
the geomagnetic field and its temporal evolution, and gain new insights
into improving our knowledge of the Earth’s interior and climate.

The SWARM concept consists of a constellation of four satellites in two
different polar orbits between 400 and 550 km altitude. Each satellite
will provide high-precision and high-resolution measurements of the
magnetic field. Together they will provide the necessary observations for
the global high-precision survey of the geomagnetic field that is needed
to model its various sources.

Magnetic fields play an important role in physical processes throughout
the Universe. The magnetic field exerts a very direct control of the
electrodynamic environment, on thermospheric dynamics, and possibly even
on the evolution of the lower atmosphere.

SWARM will provide important new knowledge of the expanding and deepening
South Atlantic Anomaly, with its serious implications for low-Earth orbit
satellite operations. Geographically, the recent decay of the Earth’s
magnetic dipole is largely due to changes in the field in that region. The
geomagnetic field models resulting from this mission will have practical
applications in many different areas, such as space weather and radiation
hazards as well as furthering our understanding of atmospheric processes
related to climate and weather.

For further information, please contact:

Einar-Arne Herland

Head, Earth Sciences Division


+ 31 71 565 5673.

ESA Media Relations Office

Tel: +33(0)

Fax: +33(0)