On March 7, the Sentinel-2B Earth observation satellite was sent into orbit to join its identical twin, Sentinel-2A, in service since June 2015. Just a few hours ago, the first images acquired by the latest satellite in the family were unveiled to scientists worldwide. In this article, we spotlight the essential role played by the image ground segment in the Sentinel-2 mission.

Sentinel-2 is an Earth observation mission using optical imaging to map the current state and changes in the Earth’s surface, identify areas of pollution around lakes and in coastal waters, help manage the risks of natural disasters and also facilitate humanitarian rescue operations. The mission comprises two identical satellites: Sentinel-2A, launched in June 2015, and now Sentinel-2B. With these two satellites we will be able to acquire a complete image of our planet’s land masses every five days.

Without the ground segment, the system would not generate any data! Every 100 minutes Sentinel-2A transfers its data to a data acquisition center. This data is then processed to produce images, which takes about an hour and a half. The image generation process takes place in four steps: the satellite acquires raw data, which it transmits to a ground acquisition center. This data is then transferred to a processing center to generate the images, which are then distributed to other centers. Lastly, the data is stored in an archiving center, where it is accessible on user request.

Thales Alenia Space is prime contractor for the image ground segment of the Sentinel-2 mission [S2-PDGS], on behalf of the European Space Agency (ESA) and at the head of a consortium including four industry partners: Thales Services, CS, ACS and DEIMOS. The ground segment comprises seven centers, located across Europe. With two satellites, that means twice the data processing and storage volume is needed.

Sentinel-2B doubles the amount of data generated. Sentinel-2A alone performs a complete cycle, covering the Earth’s surface, in ten days. It transmits 14 color “photos” per day, or one every 100 minutes. With these two imaging satellites, a cycle will now last just five days, meaning 28 photos a day, or one every 50 minutes.

The image ground segment was designed from the outset to handle this extra data. Thales Alenia Space was chosen as prime contractor for this segment in 2011, based on its proven expertise in ground segments for observation programs such as Envisat and MetOp.

Thales Alenia Space is a leading player in Europe’s ambitious environmental management program, Copernicus. The company is prime contractor for the Sentinel-1 and -3 families (four satellites per family), in charge of the image ground segment on Sentinel-2, and makes the Poseidon-4 radar altimeters for the Jason-CS/Sentinel-6 mission.

Copyrights:
Images related to Sentinel-2B: contains modified Copernicus Sentinel data (2017), processed by ESA
Last artistic view: © ESA