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 figure shows California GPS receivers location and 'piercing points' for ionospheric measurements from all receivers in California (SCIGN + BARD + IGS GPS networks). Different satellites are shown in different colours. The black star shows the epicentre location for the Denali earthquake. The piercing point is the intersection point between the GPS ray path (receiver-satellite) and a spherical shell with infinitesimal thickness at the mean altitude of the peak in the electron density profile.