Introduction

Imaging the Earth's interior has always been one of the key challenges in geosciences as it is a prerequisite for understanding our planet's internal dynamics and the coupling between its inner and outer envelopes. Gravity measurements at different altitudes (ground, airborne and space-based observations) provide a unique exploration tool, as they supply direct information on mass changes at different spatio-temporal scales. Following decades of research, developments and industrial transfers, quantum technology reached a high level of maturity and is now possible to deliver operational quantum gravimeters offering various advantages with respect to devices that have been hitherto used.

Project objectives

Aligned with the objective of strengthening EU’s strategic autonomy and competitiveness, the EQUIP-G project proposed by a consortium of 20 partners of 11 European countries, has been selected to develop and deploy a network of quantum gravimeters in Europe.

This will represent the first step towards establishing the terrestrial segment of the pan-European quantum gravimetry infrastructure, revolving around a shared Instrumental Park. For this purpose, quantum gravimeters, dual quantum gravi-gradiometers and an onboard quantum gravimeter will be employed. These instruments will be comprehensively tested, before being deployed in the field. EQUIP-G will demonstrate, through innovative measurement strategies, the ability of the quantum gravity network to contribute to EU priorities, such as Green Deal, energy management and risk mitigation. Metrological oversight will ensure that all collected quantum gravity data will be SI traceable. Data will be managed in line with the FAIR principles and with a long-term perspective to establish a Technical Core Service for gravimetry within EPOS. EQUIP-G will engage in strong community building, aimed at involving the whole European gravimetry community in the development of the long-term Instrumental Park initiative that will extend beyond the end of the project, democratizing the use of quantum gravity devices produced in Europe.

Activities lead by GFZ hydrology

GFZ section “Hydrology” has a big share within EQUIP-G and will be coordinating 2 of a total of 8 use cases which will demonstrate the proof-of-concept and the usefulness of this new technology for applied research but also societal challenges in a longer perspective.

At the Geodetic Observatory Wettzell (Bavaria, Germany) operated by BKG, the German Federal Agency for Cartography and Geodesy, an artificial sprinkling experiment is performed around 4 quantum gravimeters deployed in the field. After a short artificial rainfall event with high intensity, the instruments stay for 2 to 3 months at the same site, exposed to natural environmental conditions. For this setup, dedicated field enclosures are developed at GFZ. The goal of this use case is to measure and understand subsurface water flow and storage dynamics, hydrological fluxes at the soil-atmosphere interface (e.g., evapotranspiration) as well as water percolation to larger depths (i.e.., groundwater recharge).

The Mont Terri rock laboratory i (Jura, Switzerland) is an international research project for the hydrogeological, geochemical and geotechnical characterization of a clay formation (Opalinus Clay) as a possible host rock for the deep geological disposal of radioactive waste. For quantifying the hydrogeological dynamics, i.e., groundwater storage changes, around the underground laboratory, a network of several quantum gravimeters will be installed in tunnels and on the Earth surface. This aims also at investigating the added value of these devices in a network setup.

Furthermore, Marvin Reich will lead the EQUIP-G work package “Community Building”. This activity is tailored towards building a resilient and active community across Europe with a variety of members (scientists, policy makers, companies, stakeholders) to foster collaboration and advance this new technology under numerous perspectives: trigger instrumental developments, foster scientific exchange, provide the opportunity to use quantum gravimeters of EQUIP-G’s instrumental park by any non-profit organization within Europe, engage in open-data and open-software solutions including the establishment of an EPOS Technical Core Service and most importantly enable vivid and future-oriented discussions around this topic with all interested contributors.

Additionally, GFZ section “Geophysical Imaging” will run another use case in Krafla (Iceland) about potential applications of quantum gravimeters in the context of geothermal energy research and exploration.