How high is Mount Everest exactly? Recent surveys have come up with heights that differ by more than five metres. An expedition called the Geodetic Journey is making its way through China and Tibet to highlight the importance of geodesy and how an accurate model of the geoid from ESA's GOCE mission will lead to a unified system for measuring heights.
Geodesy is concerned with measuring and mapping the shape of the Earth's surface, to the benefit of all branches of Earth sciences and has many practical applications. Although surveying techniques go back thousands of years, it traditionally involves taking very precise three-dimensional positioning of points. It is the means by which the surface of the Earth is mapped and is also essential in the field of engineering and construction.
Accurate surveying relies on knowledge of the Earth's gravity field, which defines the horizontal. However, as a result of a number of factors, such as the fact that mountains and ocean trenches make the surface of the planet uneven and materials within the Earth's interior are not uniformly distributed, the force of gravity actually varies slightly from place to place on the surface of the Earth.
Due for launch in early 2008, ESA's gravity mission GOCE (Gravity field and steady-state Ocean Circulation Explorer) will provide an extremely accurate and unique picture of the Earth's gravity field and geoid. The geoid which is defined by the Earth's gravity field is a surface of equal gravitational potential and serves as a reference point from which to map all topographical features on the planet. GOCE will provide a model of the geoid with unprecedented accuracy and will not only be of importance in the field of geodesy, but will also lead to new insights into ocean circulation, climate change, sea-level rise, earthquakes and volcanism.
Starting in Beijing, and travelling through central China to Lhasa then on to the Tibetan Plateau and endin
Contact: Mariangela D'Acunto
European Space Agency