ESA’s miniature Earth observer put to many uses

Think of ESA’s Proba as the little satellite that does a lot. It is only the
size of a washing machine but its main instrument — the smallest hyperspectral
imager ever flown in space — has an expanding portfolio of uses encompassing
agricultural mapping, water quality monitoring, charting forest fire damage and
disaster management.

Launched in October 2001, the Project for Onboard Autonomy (Proba) satellite
measures just 60 x 60 x 80 cm. Its main instrument takes up around a third of
this pint-sized orbiter and is known as the Compact High Resolution Imaging
Spectrometer (CHRIS).

Operating from a distance of 600 km away, CHRIS acquires 14-km square images of
the Earth’s surface to a resolution of 18 metres, in a combination of up to 19
out of a total of 62 spectral bands to provide added environmental information.
And the same scene can be viewed from a variety of different angles because
Proba is manoeuvrable enough to perform controlled rolls.

That remarkable combination of abilities has aroused the interests of
researchers worldwide. Last week around 40 of them met up at ESA’s European
Space Research Institute (ESRIN) centre at Frascati, Italy. They discussed their
current and future uses of the instrument at the three-day Second CHRIS/Proba
Workshop from 28 April.

"Proba was launched as a technology demonstrator with all sorts of experimental
equipment aboard, including CHRIS," explained Evert Attema, Head of the ESA
Scientific Campaign Unit. "But once in orbit we found both Proba and CHRIS
performed well above expectations, and so we put out an Announcement of
Opportunity for scientists interested in making use of CHRIS data. Some 60
different groups responded, and we are hearing about their projects during this
event."

Looking at life on land

CHRIS’s ability to retrieve hyperspectral and multi-angular data makes it
especially useful for the study of vegetation cover on land. Francois Kayitakire
of the University of Louvain’s Water and Forest Unit in Belgium recounted
research being carried out on the 10000-hectare Nismes forest.

CHRIS’s hyperspectral capability helped differentiate tree species —
identifying coniferous and deciduous trees as well as spruce and pine groups —
while differing canopy shadows seen in multiple angle views yielded data on
woodland density, tree height and limb span.

Ray Merton of the School of Biological, Earth and Environmental Sciences of the
University of New South Wales in Australia explained how his team used CHRIS
imagery as part of an investigation of how the reflectance properties of cotton
might be used on an operational basis to estimate the crop’s health, maturity
and yield.

Merton’s team are documenting the spectral properties of cotton on a variety of
scales, from looking at individual cotton leaves in the lab to making field
acquisitions close-up, from using airborne hyperspectral imagers all the way up
to Landsat data.

He stated that the CHRIS data acquired served as a useful bridge between the
aerial and Landsat imagery. The research had been hampered by a persistent
drought affecting their test area, but even so, CHRIS data was shown to be able
to differentiate between cotton species, crops with high, normal and low water
content and also high and low fertility of the underlying soil.

Working over water

CHRIS was designed for Earth Observation over land surfaces, but a number of
research teams are investigating its use to study inland water bodies as well as
coastal water sites.

Ramon Pena-Martinez of the Centre for Hydrographic Studies of Spain’s Centro de
Estudios y Experimentaci??n de Obras P??blicas (CEDEX) explained how he was
preparing to use CHRIS data in support of a project employing the Medium
Resolution Imaging Spectrometer (MERIS) instrument on ESA’s Envisat spacecraft
to detect traces of potentially harmful phytoplankton in his country’s reservoirs.

"Because most rain in Spain falls in the north, the country has hundreds of
large reservoirs to redistribute water where it is needed," Pena-Martinez
explained. "We are interested in monitoring levels of photosynthetic pigments on
the surface of a number of sample reservoirs as an indication of phytoplankton
concentrations and overall water quality.

"We are interested in using whatever hyperspectral sensor is available for this
task, including airborne instruments, and monthly acquisitions from CHRIS
represents a valuable additional resource for us."

Joining forces for fire mapping

CHRIS is also set to join forces with another mini-satellite to survey the
longer-term damage done by forest fires. When Proba was launched it shared its
rocket with the Bi-Spectral Infrared Detection (BIRD) spacecraft designed by the
German Aerospace Centre (DLR) to detect high-energy and fire events across the
Earth’s surface.

This being so, the joint research programme outlined to the Workshop by Dieter
Oertel of DLR represents a sort of reunion. CHRIS will re-acquire the sites of
forest sites charted within the last year by BIRD to map the extent of the burnt
area and identify any vegetation regrowth. Areas under target include last
year’s fire zones in Spain and Portugal as well Australia and Siberia.

"Fire is the single most active environmental change agent," Oertel said.
"Within many ecosystems such as boreal forests low to medium intensity fires are
actually beneficial, reducing fuel loads and stabilising the environment.
However high intensity fires can be more destructive, leading to destruction of
the dominant plant species, soil degradation, increased water run-off, flooding
and landslides.

"The data from the two satellites will help develop a system to decide when a
fire is either beneficial or destructive."

Aftermath of disaster

The Workshop also heard how the international Charter on Space and Major
Disasters was considering an increase in its use of CHRIS imagery for
high-resolution damage assessment as a response tool during disaster situations.
Back in December 2003 a CHRIS image of flooding in the town of Ville d’Arles in
France was acquired following a Charter activation.

The nature of Proba’s origin as a technology demonstrator mission means that
CHRIS has previously lacked archive data to enable before and after comparisons
(although an archive is now being integrated within the ESRIN Multi-Mission
ground segment) but the possibility of employing SPOT or Landsat data for
comparison purposes was discussed at the Workshop.

Qingxi Tong of the Institute of Remote Sensing Applications of the Chinese
Academy of Sciences in Beijing stated that China had a widespread interest in
hyperspectral imaging for a variety of uses from mineral prospecting to disaster
relief. As part of the flood research element of the joint ESA-China Dragon
Programme, CHRIS acquisitions of flood-prone areas near Beijing are being
scheduled for the summer.

About Proba

Proba (Project for On Board Autonomy) is an ESA micro-satellite built by an
industrial consortium led by the Belgian company Verhaert, launched in October
2001 and operated from ESA’s Redu Ground Station (Belgium).

Orbiting 600 km above the Earth’s surface, Proba was designed to be a one-year
technology demonstration mission of the Agency but has since had its lifetime
extended as an Earth Observation mission. It now routinely provides scientists
with detailed environmental images thanks to CHRIS — developed by UK-based Sira
Electro-Optics Ltd — one of the main payloads on the 100 kg spacecraft.

Proba boasts an ‘intelligent’ payload, has the ability to observe the same spot
on Earth in a large combination of different visible and infra-red spectra as
well as from a number of different angles. A follow-on mission, Proba-2, is due
to be deployed by ESA around 2005.

Proba’s unique capabilities also makes it a useful resource in the development
of the proposed hyper-spectral and multi-angular Surface Processes and Ecosystem
Changes Through Response Analysis (SPECTRA) mission, an Earth Explorer
spacecraft intended to study terrestrial vegetation across the world’s major
biological communities or biomes. If selected for development, SPECTRA would
launch around 2012.

Related articles

* Aftermath of California inferno
http://www.esa.int/esaSA/SEM1MZWLDMD_earth_0.html

* China’s Three Gorges Dam
http://www.esa.int/esaCP/SEM4PFYO4HD_FeatureWeek_0.html

* CHRIS/Proba takes lead in Spanish campaign to help hyperspectral sensor
development
http://www.esa.int/esaCP/SEM6NFYO4HD_index_0.html

* Meet CHRIS — the little camera that takes big pictures
http://www.esa.int/esaCP/ESAIZ8NSRWC_UnitedKingdom_0.html

* Pinpoint accuracy with the Proba camera
http://www.esa.int/esaCP/ESAX8SG18ZC_index_0.html

Related links

* CHRIS Workshop
http://www.congrex.nl/04c14/

* Proba
http://www.esa.int/SPECIALS/Proba_web_site/index.html

* About Spectra
http://www.esa.int/esaLP/ASE12YNW9SC_spectra_0.html

[NOTE: Images supporting this release are available at
http://www.esa.int/export/esaCP/SEMHHH77ESD_index_1.html ]