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A VUELO DE UN QUINDE EL BLOG., A good photographer needs agility. So it is with ESA microsatellite Proba-1, which turns in space to capture terrestrial targets. Celebrating its tenth birthday this week, Proba-1’s unique images are used by hundreds of scientific teams worldwide.
For most Earth-observing satellites, image acquisition is only a matter of opening a viewing aperture but Proba-1 is different. The satellite’s platform and payload work as one: spinning reaction wheels guided by a startracker roll it up to 25º side to side and 55º along its path. This helps Proba-1 compensate for its 7.5 km/s speed, like a photographer panning to snap a moving target. In addition, Proba-1 can record up to five differently angled views of the same target, important for researchers investigating how vegetation changes appearance with shifts in view. Understanding 'Bi-Reflectance Distribution Function' has proved beneficial for mapping and classifying land cover, from forest monitoring in Canada to crop yield predictions in Europe, Australia and China.
Credits: ESA.
A good photographer needs agility. So it is with ESA microsatellite Proba-1, which turns in space to capture terrestrial targets. Celebrating its tenth birthday this week, Proba-1’s unique images are used by hundreds of scientific teams worldwide.
A technology demonstrator turned into an Earth observation mission, the microsatellite – just a cubic metre in volume – has acquired nearly 20 000 environmental science images with its main Compact High Resolution Imaging Spectrometer (CHRIS), used by a total of 446 research groups in 60 countries.
CHRIS is used to measure directional spectral reflectance of land areas, thus providing new biophysical and biochemical data, and information on land surfaces.
Credits: SIRA.
ESA has a family of experimental ‘Project for Onboard Autonomy’ microsatellites: the Sun-watching Proba-2 went into orbit in 2009 and the vegetation-imaging Proba-V will be launched next year.
But it was Proba-1, launched from India on 22 October 2001, that started it all
CHRIS's multi-angled view of Golden Gate Bridge in San Francisco, USA. For most Earth-observing satellites, image acquisition is only a matter of opening a viewing aperture but Proba-1 is different. The satellite’s platform and payload work as one: spinning reaction wheels guided by a startracker roll it up to 25º side to side and 55º along its path. This helps Proba-1 compensate for its 7.5 km/s speed, like a photographer panning to snap a moving target. In addition, Proba-1 can record up to five differently angled views of the same target, important for researchers investigating how vegetation changes appearance with shifts in view. Understanding this has proved beneficial for mapping and classifying land cover, from forest monitoring in Canada to crop yield predictions in Europe, Australia and China.
Credits: ESA
“Proba-1 remains the most agile and stable satellite platform in its range,” explains Frank Preud’homme of QinetiQ Space Belgium, the company that built Proba-1 for ESA.
“These attributes are a prerequisite for high performance remote sensing.”
For most Earth-observing satellites, image acquisition is only a matter of opening a viewing aperture but Proba-1 is different.
Proba-1 CHRIS image of Mount Kilimanjaro in Tanzania, the highest peak in Africa, acquired on 27 April 2011
Credits: ESA
The satellite’s platform and payload work as one: spinning reaction wheels guided by a startracker roll it up to 25º side to side and 55º along its path.
This helps Proba-1 compensate for its 7.5 km/s speed, like a photographer panning to snap a moving target.
This Proba image shows numerous small lakes in the otherwise arid environment of the Gobi Desert in the Chinese Autonomous Region of Inner Mongolia, surrounded by some of the highest and largest sand dunes in the world. This image was acquired on 29 September 2005 by the Compact High Resolution Imaging Spectrometer (CHRIS).
Credits: ESA
In addition, Proba-1 can record up to five differently angled views of the same target, important for researchers investigating how vegetation changes appearance with shifts in view.
“Look at a sunflower on the ground – you’ll see a different mix of colours depending on where you stand, as well as the growing season and time of day,” explains Mike Cutter of Surrey Satellite Technology Ltd, which designed CHRIS. “The same is true in orbit.”
Proba-1 CHRIS image of the southern tip of Portsmouth Harbour, the Isle of Wight and the heavily-trafficked waters of the Solent in between, acquired 26 November 2010
Credits: ESA
Understanding this has proved beneficial for mapping and classifying land cover, from forest monitoring in Canada to crop yield predictions in Europe, Australia and China.
Other researchers favour the fact that CHRIS’s spectral response can be programmed as desired, to home in on diverse factors such as inland or coastal water quality –identifying oil spills, for example – atmospheric pollution or even desert lichens – significant for conserving topsoil in marginal environments.
A cloudy day on North Sentinel Island in the Indian Ocean as seen from ESA's Proba satellite on 23 April 2005.
Credits: ESA, Sira Technology Ltd
CHRIS’s 17 m resolution is useful in its own right, adds Mr Cutter: “It can give extra detail of a local section of a larger satellite image acquired at lower resolution.”
For instance, more than 500 CHRIS images have been delivered for the International Charter ‘Space and Major Disasters’, a space agency agreement to prioritise damage mapping of disaster-struck regions.
Proba's CHRIS image of the French town of Arles, acquired on 7 December 2003 during flooding that swamped the northern part of the settlement under one metre of water. The image was acquired following activation of the Charter on Space and Major Disasters.
Credits: ESA
“This mission came down to an experiment – Proba’s name derived is from the Latin word Probare: ‘let’s try’,” comments Frederic Teston, head of ESA’s In-Orbit Demonstration Programme, giving Europe’s space industry the opportunity to flight-test new technologies.
“We were demonstrating as many new technologies as possible on a single platform, the resulting satellite being able
This black and white image shows Uluru, also known as Ayers Rock, in Australia. It was acquired 24 April 2004 by the High-Resolution Camera (HRC) aboard Proba. Uluru is the world's largest monolith, and a sacred site to Australia's Aborigines. It is 3.6 km long and two km wide. The walk around it covers 9.4 km.
Credits: ESA
CHRIS users simply submit the latitude, longitude and altitude of their chosen target and Proba-1’s computer navigates to the correct location, tilts, shoots and delivers the scene.
Other innovations included then-novel gallium arsenide solar cells and one of the first laptop-style lithium ion batteries – now the longest operating example in Earth orbit.
Proba-1, Project for On Board Autonomy, demonstrates the potential and feasibility of small satellites for advanced scientific and Earth Observation missions.
Credits: ESA
CHRIS is only the largest of Proba-1’s payloads. A smaller imager, the High Resolution Camera developed by Belgian company OIP Sensor Systems, provides black-and-white 5–10 m-resolution images.
The microsatellite is overseen from ESA’s Redu ground station in Belgium and the use of Proba-1's instruments is managed from ESA's ESRIN Earth observation centre in Italy.
Guillermo Gonzalo Sánchez Achutegui
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