Geodesy is the science of determining the geometry, gravity field, and rotation of the Earth and their evolution in time. Traditionally, geodesy has been serving other sciences and has had many societal applications, including mapping. With the advent of satellite technology, geodesy itself developed into a science, making unique contributions to the study of the Earth system, its inherit dynamics, and its response to climate change, as well as a tool underpinning a wide variety of other remote sensing techniques. Geodesy is an important element in making all Earth observations interoperable, facilitating the combination of satellite observations with those gathered on ground.Facilitated by Global Navigation Satellite Systems such as GPS, a wide and growing set of applications associated with positioning and navigation is opening up. Geodesy provides the foundation on which all Earth observation systems are built. In this function, geodesy is essential for Earth observation just like the foundation and frame of a house are necessary to keep it stable over time. But modern geodesy does more: with its three pillars of geokinematics, Earth gravity field, and Earth rotation, it also provides comprehensive observations of changes in the Earths shape, gravity field and rotation.
