Establishing reliable and integrated gravity metrology for emerging applications

Local gravity, which differs between times and locations, is primarily used in geodesy to determine the Earth’s shape but the need for accurate gravimetric measurements is growing. Since the redefinition of the SI in 2019, the kilogram, the unit for mass, can now be realised using the Kibble balance, a method which requires precise knowledge of local gravity. Mass measurements are vital throughout industry, from manufacturing pharmaceuticals to ensuring fair trade of fuel. Additionally, the BIPM CCM Strategy 2022-2032 highlights gravity measurements as essential for climate monitoring – including for measuring key climate variables like ice mass and water storage. These applications have pushed the requirement for absolute gravity uncertainties to as low as 10 nm/s², but gravimetry capability is hampered by a lack of measurement precision, comparable measurement procedures and access to calibrations.

This project will improve capabilities for gravity metrology by developing harmonised measurement and uncertainty evaluation procedures for absolute and relative gravity measurements, contributing to the traceability of the SI kilogram. Gravimeter capability will be improved, achieving uncertainties to below 10 nm/s², and new procedures developed for evaluating gravity using a Kibble balance, achieving uncertainties below 50 nm/s². The project will also establish at least five gravity reference stations in order to develop a traceable absolute gravity function of time, as well as a software tool able to predict absolute gravity for a given location.

In the long term, this work will improve local gravity measurements around the world, impacting geodesy as well as applications relying on accurate realisations of the kilogram, including industry, engineering, and climate monitoring.