The Sentinel satellites are designed within the European Commission Copernicus programme, whose aim is to monitor our planet for environmental, social, and economic purposes. The Sentinel-3 series is focused on ocean observation, with further applications also on land and atmosphere. The mission is based on two identical satellites flying on a polar, Sun-synchronous orbit at altitude 815 km, inclination of 98.6° and a repeat cycle of 27 days. The first satellite, Sentinel-3A was launched in February 2016.