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Vom Kreidestrich an der Hafenmauer zum atomaren Standard

From Chalk Marks on Harbour Walls to Atomic Standards

Press release from
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© Rosemarie Jackiw-Flury
Surveying point in Ruthe near Sarstedt.

New geodetic approach via atomic clocks

In collaboration with national and international experts, researchers at Leibniz University Hannover intend to develop a groundbreaking and highly accurate geodetic standard. These geodetic reference systems could enable researchers to quantify and analyse climate change: What will Greenland look like in 20 years? What will our coasts be like? How will the Alps respond to climate change?

"Our long-term objective is to determine the development of continental and global height systems with centimetre precision", explains Professor Jakob Flury from the Institute of Geodesy. He and his colleague Gérard Petit from the Bureau International des Poids et Mesures (BIPM) are in charge of the work group "Relativistic Geodesy: First Steps Towards a New Geodetic Approach" within the framework of the International Association of Geodesy (IAG). The group presented their findings in Montreal as well as in a widely acclaimed "Eos" article, a magazine of the American Geophysical Union (https://eos.org/features/einstein-says-its-309-7-meter-oclock).

In simple terms, the work group aims to measure height via time by using highly accurate atomic clocks in order to develop an improved geodetic height reference system. Atomic clocks can measure the influence of the Earth's gravitational field on time with great accuracy. In the long run, researchers could overcome inhomogeneous height systems, which inevitably occur in conventional geodetic procedures. "The first steps are both fascinating and promising", says Jakob Flury, "however, it will take some time to establish this as a standard geodetic procedure."

Measurements via atomic clocks are based on Einstein's theory of relativity: clocks situated in closer proximity to the centre of the earth move at a slightly slower pace than those further away. This enables researchers to measure differences in altitude.

The work group focuses on the transmission and comparison of atomic clock signals. For this purpose, researchers analysed atomic clock signals in different locations including Braunschweig (PTB) and Paris (Observatoire de Paris). These clocks - among the most accurate instruments worldwide - are connected via 1,400 kilometres of glass fibre. The signals are compared in Strasbourg. The researchers currently focus on applying the findings of their first experiments to a continental network.

With regard to establishing a standard height reference system, this method could open up entirely new possibilities. Since sea levels vary, each country usually uses its own height system. For example, sea levels in the Mediterranean and the North Sea differ. Depending on the location of the reference level determined by the respective country, this results in height differences of up to 50 centimetres, which can be inconvenient - both for international building projects and for recording extensive altitude changes. By integrating atomic standards, researchers could go far beyond the current limitations of geodetic methods.

Note to editors:

For further information, please contact Prof. Dr.-Ing. Jakob Flury, Institute of Geodesy at the Faculty of Civil Engineering and Geodetic Science (Tel. +49 511 762 5697 or 762 4905, Email flury@ife.uni-hannover.de).