CHRIS: 10 years of science innovation
Celebrating a decade in space, we take a closer look at the hyperspectral imager CHRIS and how gazing at Earth from different angles and with a large number of programmable spectral bands has made all the difference for a fantastic range of scientific studies, from classifying plants to mapping the submerged shoreline.
CHRIS is the innovative hyperspectral imager payload on the European Space Agency (ESA) microsatellite Proba-1 - that started its life as a technology demonstration satellite, but turned into an Earth observation mission serving the scientific society. Its agility makes PROBA-1 different to most Earth-observing missions, with the satellite platform and payload working as one.
Guided by a star tracker, the microsatellite spins its reaction wheels to roll 25 degrees off-nadir across track directions, and 56 degrees along-track. This means that CHRIS can acquire five different views of the same target at different viewing angles. It’s these different angles that the scientists find valuable, as they can capture or avoid reflections and look at differences in colour.
“Say you’re looking at a sunflower on the ground,” explains Mike Cutter of SSTL’s Optical Payloads Group, which developed CHRIS and oversees its operation. “You’ll see a different mix of colours depending on where you’re stood, as well as the growing season and time of day: the yellow canopy, green stalk and leaves, brown soil, sun glint or shadows. The same is true when observing from orbit. This offers a way of giving much more accurate classification of vegetation and canopy covers, such as the tree species within forests.”
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