The Copernicus Sentinel-3C and Sentinel-3D satellites side by side in the cleanroom at Thales Alenia Space in Cannes, France. These two satellites will eventually replace Sentinel-3A and Sentinel-3B, which are currently in orbit around Earth. Carrying a suite of cutting-edge instruments, the Copernicus Sentinel-3 mission measures systematically Earth’s oceans, land, ice and atmosphere to monitor and understand large-scale global dynamics. It provides essential information in near-real time for ocean and weather forecasting.