Primary productivity in the oceans forms the basis of marine life and also plays a role in the carbon cycle. While important for the marine food chain, some algae blooms can be toxic to humans, marine ecosystems and fisheries. The imaging spectrometer on Sentinel-3 will be used to monitor acquatic biological productivity and marine pollution. The same instrument can measure differences in the ‘colour’ of the land, allowing scientists to monitor the way land is being used and helping resource managers to plan. It also provides indices on the health of our vegetation, which is essential for agricultural practices and food production.