The remarkable combination of abilities of European Space Agency’s (ESA) Proba – the Project for Onboard Autonomy – 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 held recently.
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, 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.
“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.”
CHRIS’s ability to retrieve hyperspectral and multi-angular data makes it especially useful for the study of vegetation cover on land. 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. He stated that the CHRIS data acquired served as a useful bridge between the aerial and Landsat imagery.
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.
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.
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.
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.