The European Space Agency (ESA) is Europe’s gateway to space. Its mission is to shape the development of Europe’s space capability and ensure that investment in space continues to deliver benefits to the citizens of Europe and the world.
Find out more about space activities in our 23 Member States, and understand how ESA works together with their national agencies, institutions and organisations.
Exploring our Solar System and unlocking the secrets of the Universe
Go to topicProtecting life and infrastructure on Earth and in orbit
Go to topicUsing space to benefit citizens and meet future challenges on Earth
Go to topicMaking space accessible and developing the technologies for the future
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The Copernicus Sentinel-3 satellites carry a synthetic aperture radar altimeter that is used to measure sea-surface height, ocean-surface waves, the extent and height of sea ice, and the height of large inland rivers and lakes. These measurements are worked out from the time it takes the radiofrequency pulse to travel from the antenna to the surface and back again after reflection from the sea surface. The time delay is then converted to distance, which, in turn, is used to calculate the variations in the height of the sea surface etc. However, the speed of the pulse is slowed down by water in the atmosphere. Therefore, the Sentinel-3 satellites also carry a microwave radiometer to measure atmospheric water. These measurements are used to correct for the delays in the radar altimeter’s signal.