FIeld QUantum gravity Sensors – Precision Mechatronics Laboratory (PML)

The measurement of the gravity acceleration and of its variations, has proven to be a very powerful technique in the field of Earth sciences, and gravimeters have been used by geophysicists for several decades. Thanks to Newton’s law, we know that gravity at the surface of the Earth is influenced by the masses surrounding the instrument. Gravimetry, with a very high precision at the level of one part of a billion, thus allows the monitoring of many phenomena, from water resource availability to volcanic activity, and generally offers a capability to characterize subsurface mass variations.

Picture of the AQG near the active craters of Mount Etna, before its installation in the Pizzi Deneri Observatory © Exail / NEWTON-g European project

The FIeld QUantum Gravity Sensors (FIQUgS) project is a European collaboration bringing together 10 partners to take quantum gravity sensing to the next level. This consortium has two objectives:
1. To develop a next generation Absolute Quantum Gravimeter (AQG) that will offer an ultimate level of performance, compactness, an improved robustness, and a reduced power consumption.
2. To produce an autonomous multi-sensor density imager composed of a Differential Quantum Gravimeter (DQG) and a Ground Penetrating Radar (GPR). This carrier will have the capability to automatically perform geophysical surveys and will put together merged maps gathering gravity, gravity-gradient, and radar data.

PML’s contribution to FIQUgS:

AQGs are ultra-stable absolute gravity sensors whose performance is mainly limited by seismic motion. One approach to addressing this issue consists of measuring the vibrations of the sensor head using a classical accelerometer and compensating for their effects on the AQG output in real time. The performance of this method is inherently limited by the resolution of the accelerometer. At the start of the project, a commercial accelerometer, the Titan from Nanometrics, was used to perform vibration compensation. However, since it was not optimally designed for this application, residual errors from the imperfect compensation remained the main limitation to the accuracy of the gravity measurements.

Our group, which has extensive experience in designing high-resolution inertial sensors, has undertaken the challenging task of developing an ideal accelerometer for optimal vibration compensation and, consequently, improving the performance of the AQG.