Image of Plymouth UK acquired by Proba-1 CHRIS on 14th April 2017 – with an image of the satellite at top left. CHRIS/Proba-1 is jointly operated by ESA and SSTL, with support from Airbus DS and RSAC
Last week, I was in Ghent, Belgium, at the PROBA-1 CHRIS End of Mission Workshop hosted by the European Space Agency (ESA).
As the name suggests, the workshop marked the end of data collection for the long-lived Compact High Resolution Imaging Spectrometer (CHRIS) onboard the PROBA-1 satellite by bringing together people who have worked, and are working, with the instrument to present, discuss, and demonstrate what has been achieved.
The PROBA-1 mini-satellite was launched from Satish Dhawan Space Centre in India on 22 October 2001 and put into a sun-synchronous 615 km low earth orbit. The satellite was built by QinetiQ Space Belgium and was seen as an experimental small satellite. Its name was derived from the Latin word ‘probare’, which means ‘to test’ or ‘to try’, and therefore PROBA stands for Project for On-Board Autonomy, although due to the instrument, it’s also known by the name CHRIS PROBA-1.
The CHRIS instrument was built by SIRA Ltd, which has since become Surrey Satellite Technology Ltd, and provided hyperspectral data. It had up to 62 spectral bands over wavelengths ranging from 400 to 1050 nm at a designed spatial resolution of 17 m, although the number of bands decreased when full spatial resolution data was acquired, meaning the satellite had several modes. PROBA-1 also carries a monochromatic 5 m spatial resolution High Resolution Camera (HRC), alongside the Debris In-Orbit Evaluator (DEBIE-1) for measuring space debris and the Standard Radiation Environment Monitor (SREM) for monitoring radiation belts. Through ongoing support from the European space Security and Education Centre (ESEC) in Redu, these instruments continue to acquire data for experimental activities as the PROBA-1 satellite remains working in space and will not de-orbit for at least another 10 years.
It was great to hear about everyone’s work with CHRIS, from the early challenges through twenty years of data collection until it stopped nominal acquisitions in December 2022, and finally looking forward to ESA’s next hyperspectral mission, Copernicus Hyperspectral Imaging Mission for the Environment (CHIME), which is due to be launched in 2028. CHRIS collected over 8 000 cloud-free science acquisitions across over 900 sites around the globe. As a limited amount of data could be acquired and downlinked, Remote Sensing Applications Consultants Limited actively talked with the Principal Investigators (PIs) and scheduled the satellite to acquire the most likely cloud-free sites alongside collecting requested data. Airbus DS UK were responsible for processing the data, and because the mission was only designed for a few years and originally only had two PIs (Prof. Mike Barnsley and Dr. Jeff Settle), this was very manual compared to modern systems. Therefore, the reprocessing needs to include the design of an updated system.
From my point of view, I have been working with CHRIS data for many years, first getting involved before the launch championing its use for marine applications, and I presented the ongoing activities being undertaken through Telespazio UK, including the upcoming reprocessing campaign to generate Analysis Ready Data (ARD) products and recent cross-mission calibration activities with the PRISMA hyperspectral mission.
Hyperspectral data has been part of my Earth Observation journey almost from the start as I did my PhD using hyperspectral data collected by the Compact Airborne Spectrographic Imagery (CASI) on aircraft, before moving to satellite hyperspectral data and CHRIS PROBA -1has been a big part of it.
Although the satellite was only expected to perform experiments for one year, it carried on and on and has the distinction of being ESA’s longest-serving mission. I was pleased to catch up with everyone and be part of the celebration of its work and life. Of course, the datasets it collected are available, and this means there is still plenty it can do, and it is certainly not leaving my work life yet!
