WG Q.3: Relativistic geodesy with clocks

Chair: Gerard Petit, Paris, France
Vice-Chair: Jakob Flury, Hannover, Germany
Consultant from Physics: Christian Lisdat, Braunschweig, Germany


Optical clocks are sensitive to the gravity potential in which they are operated. The comparison of two clocks will reveal a frequency offset from the value expected from side-by-side comparisons that can directly be related to the potential difference between both clocks. The best optical clocks now reach resolutions of 0.1 m 2 /s 2 , transportable ones about 2 m 2 /s 2 . They can be achieved already after few hours of averaging. We will evaluate how this technique can be used to generate unified and long-term stable height networks and reference systems. This will include discussion about the feasibility to realize a datum by reference to a, e.g., space-borne clock with ideally negligible gravitational interference. Future clock networks might also be used as ground-truth for space missions or even to bridge gaps in satellite observations. Other aspects to be addressed are the application of observed time-variable signals in de-aliasing of satellite observations. In cooperation with the two previous WGs, sensor fusion concepts will be discussed to utilize the different spatial integration characteristics of clocks and the other gravity sensors to disentangle local and extended signal sources.

In summary, the goals of this WG are using clocks measurements for determining differences of physical heights and gravity potential for various geodetic applications.


  • Clock networks for unification of height systems
  • Gravity field recovery on ground
  • Application to realize reference systems, including dedicated space clocks
  • Further applications (height/potential variations)
  • Potential satellite missions for long-wavelength gravity field recovery, includingoptical links for comparing the space clocks


Claude Boucher (France)
Davide Calonico (Italy)
Pascale Defraigne (Belgium)
Pacôme Delva     (France)
Ropesh Goyal    (India)
Gesine Grosche (Germany)
Hua Guan (China)
Chris Hughes    (UK)
Sergei Kopeikin (USA)
Jürgen Kusche (Germany)
Claus Lämmerzahl (Germany)
Marie-Françoise Lequentrec (France)
Guillaume Lion (France)
Andrew Ludlow (USA)
Helen Margolis (UK)
Elena Mazurova (Russia)
Nathan Newbury (USA)
Bijunath Patla (USA)
Nikos Pavlis (USA)
Paul-Eric Pottie (France)
Ulrich Schreiber (Germany)
WenBin Shen (China)
Simon Stellmer (Germany)
Yoshiyuki Tanaka (Japan)
Pieter Visser (Netherlands)

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