One-of-a-kind atomic gravimeter comparison at HITec

Gravimeters measure the force of attraction on the Earth's surface. Repeated measurements allow conclusions on spatial and temporal changes in the Earth's gravitational field. Gravimeters are used, for example, in geodesy or the measurement of large-scale phenomena such as plate tectonics and glacial uplift, but also in the monitoring of volcanic activity, the mapping of underground cavities or the investigation of earthquakes. In the future, gravimetry will also be used to monitor groundwater changes and to control the withdrawal of drinking water and for agricultural irrigation.

Conventional gravimeters exhibit what is known as drift. They become inaccurate over time for mechanical reasons and have to be calibrated regularly. Quantum gravimeters have been a promising alternative for some years now. They enable continuous monitoring of absolute gravity, are user-friendly and transportable, but are still very expensive at around 500,000 euros. Research groups are still unsure about this new technology and need more experience regarding measurement accuracy.

Researchers and manufacturers from Germany, France, Italy, Poland and the USA therefore met at the Hannover Institute for Technology (HITec) at the end of January for a workshop and a comparison campaign with five commercially available atomic quantum gravimeters. The aim of this unique campaign was to test the measurement accuracy and consistency of the various devices and bring users one step closer to application.

The HITec offers ideal conditions for the comparison due to its complex structural design. It is a vibration-optimised laboratory building that shields the measuring instruments from anthropogenic and natural ground disturbances. Passing cars or trucks and other microseismics can only interfere to a limited extent.

Ludger Timmen, head of the gravimetry laboratory at HITec and co-organiser of the comparison campaign, was satisfied with the initial results: "The collaboration went very well, all the instruments worked, and no gravimeter had to be withdrawn from the comparison. The findings of this comparison campaign will also influence our own developments on quantum gravimeters in the TerraQ Collaborative Research Centre."  The TerraQ CRC, together with the Hydrology-Gravimetry Group of the GeoForschungsZentrum Potsdam, invited and supported this comparison.