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Satellite portrait of global plant growth will aid climate research

An ambitious ESA project to chart ten years in the life of the Earth‘s
vegetation has reached a midway point, with participants and end-users
having met to review progress so far. Harnessing many terabytes of
satellite data, the GLOBCARBON project is intended to hone the accuracy
of climate change forecasting.

GLOBCARBON involves the development
of a service to generate fully calibrated estimates of land products
based on a variety of Earth Observation data, suitable for assimilation
into sophisticated software simulations of the planet created by the
global carbon modelling community.

The service is focused on the generation
of various global estimates of aspects of terrestrial vegetation: the
number, location and area of fire-affected land, known as Burnt Area
Estimates (BAE), the area of green leaf exposed to incoming sunlight
for photosynthesis, known as Leaf Area Index (LAI), the sunlight
actually absorbed for photosynthesis, known as the Fraction of Absorbed
Photosynthetically Active Radiation (fAPAR) and the Vegetation Growth
Cycle (VGC).

To obtain these products, GLOBCARBON
blends data from a total of five European satellite sensors: the
VEGETATION instruments on SPOT-4 and SPOT-5, the Along Track Scanning
Radiometer-2 (ATSR-2) on ERS-2, plus the Advanced Along Track
Radiometer (AATSR) and Medium Resolution Imaging Spectrometer (MERIS)
on Envisat.

At a 17 January GLOBCARBON progress
meeting that took place at ESRIN, ESA‘s European Centre for Earth
Observation, project partners and end-users heard that products for six
complete years are now available, covering the whole of 1998 to 2003. A
follow-on phase is planned to cover up to the end of 2007.

GLOBCARBON is a multi-sensor,
multi-year global service, and as such has been very challenging in
scope,” stated Geert Borstlap of VITO, the Belgium-based organisation
leading the contract for ESA. “In processing terms we had about 45
terabytes of input data and 18 terabytes of output data, and within the
process generated about one petabyte of intermediate data. We developed
the necessary software and had about 25 computers and 25 terabytes of
disks continuously running for one year from start to finish.”

The processing algorithms used to render
raw satellite data into final products have come from a number of
authoritative sources: the International Geosphere-Biosphere Programme
(IGBP); the European Commission‘s Joint Research Centre in Ispra, Italy
(EC-JRC); the University of Toronto; the Centre d‘Etudes Spatiales de
la Biosphère (CESBIO) in Toulouse and the Laboratoire des Sciences du
Climat et l‘Environnement (LSCE) in Gif-Sur-Yvette as well as ESA‘s
ESRIN centre in Frascati, Italy. Dr Stephen Plummer of IGBP oversees
algorithm selection and interfaces with product users.

GLOBCARBON end users – charged with
assessing and validating the products – comprise the Global Carbon
Project (GCP) hosted in Canberra, Australia, the UK Centre for
Terrestrial Carbon Dynamics (CTCD) in Sheffield, the Max Planck
Institute for Meteorology (MPI-M) in Berlin, Germany and the Potsdam
Institute for Climate Impact Research (PIK).

GLOBCARBON LAI results are also
being checked with LAI products from CYCLOPES, another satellite-based
service being developed through a project called Geoland, part of the
European Commission‘s initial contribution to Global Monitoring to
Environment and Security (GMES), a joint initiative with ESA to develop
an independent environmental monitoring capability for Europe.

Researchers seeking to follow the carbon

Carbon‘s unique compound-forming properties
underpin all life on Earth. They also mean this many-formed element is
abundant not only in the biosphere but also in the geosphere, ocean and
atmosphere, undergoing exchange – often rapidly – between them.

This movement of carbon through the
different components of the Earth system is called the carbon cycle.
Human activities have led the cycle to move out of balance, as fossil
fuel burning and land clearances lead to increased atmospheric carbon
levels driving global warming. This development may also have knock-on
effects on the carbon cycle itself, in the uncertain responses of
oceanic phytoplankton and land vegetation respond to rising

Researchers have developed complex software models of carbon cycle
processes to try and predict future changes, providing vital input for
the Intergovernmental Panel on Climate Change (IPCC) and related groups
assessing the potential impact of climate change. However any model is
only as good as input data, and relevant data is lacking for certain
aspects of the carbon cycle – especially land vegetation.

is definitely a useful product for the carbon modelling community,”
explained Dr Tristan Quaife of CTCD. “Information about LAI is
important because it gives us an ability to constrain the amount of
green biomass available for photosynthesis and gas exchange through

“These are probably the two key processes
controlling carbon exchange with the atmosphere, so with better
knowledge of LAI and its dynamics we have a better chance of estimating
the primary productivity of an ecosystem.

“It is a similar story with vegetation
growth cycle – or phenology. Improved information allows us to improve
our knowledge of the length of time that leaves are out, influencing
vegetation‘s ability to assimilate carbon from the atmosphere. That
isn’t well modelled at the moment because we don‘t fully understand
what it is that makes a plant sprout its leaves, and consequently
models aren‘t so accurate.

“Burnt area estimates are also useful
because we don‘t fully understand global fire occurrence patterns
either. We can map active fires from space, but what we are seeing
there is only the part of the Earth that is combusted at that moment.
To get a complete picture we need to record the full area burnt, which
is useful for determining how much biomass has been removed from the
Earth‘s surface and consequently how much carbon has been liberated
into the atmosphere.”

ESA serving global change research

is being supported through the ESA‘s Data User Element of the Earth
Observation Envelope Programme-2 (EOEP-2), and is one of a family of
projects developing satellite-based products and services that support
investigations of global and climate change within different elements
of the Earth system.

These include GLOBWETLAND which is
developing means of monitoring wetland areas; GLOBCOVER which aims to
create the sharpest-ever global land cover map; GLOBAEROSOL to chart
the distribution of atmospheric aerosols playing a role in climate
forcing; GLOBCOLOUR which users ocean colour data to estimate marine
photosynthesis; and GLOBICE to acquire information on sea ice dynamics.

(Credits ESA)