Gravity and gravity gradient simultaneous survey in an urban environment

In development since 2019, Exail’s Differential Quantum Gravimeter (DQG) is a double quantum gravimeter capable of measuring both gravity and vertical gravity gradient (VGG) at the same time [1]. In the laboratory it has shown sensitivities down do 250nm/s²/sqrt(tau) and 30E/sqrt(tau) as well as sub-10nm/s² and sub-1E stabilities. 

Here we show the performance of this instrument in the field by performing a dual gravity survey in the streets of Lisbon in order to detect a sewer system from the XVIIIth century. The survey was performed in collaboration with Lisbon city archeology laboratory (CAL). In total 26 stations in three days have been taken. The sewer system can be clearly observed on the gravity gradient signal, less so on the gravity signal, which is less resilient to the especially high environmental noise. The survey was performed in early October 2024 in mild temperature conditions but in the presence of wind and rain which necessitated the use of a tent.

Despite this DQG prototype not being originally designed for outdoor use, no issues were encountered during the measurements which bode well for future outdoor versions of this instrument, in particular for the automatized version in development within the FIQUgS project and which should improve significantly the rate of measurement.

We acknowledge fruitful discussions with Thomas Jacob from BRGM and Daniele Sampietro as well as Martina Capponi from GReD. Exail acknowledge funding from the Horizon-EUROPE project FIQUgS, grant number 101080144. YO acknowledge support from FCT – Fundação para a Ciência e a Tecnologia (Portugal), namely through project UIDB/04540/2020.[1] C. Janvier, V. Ménoret, B. Desruelle, S. Merlet, A. Landragin, and F. Pereira dos Santos, Compact differential gravimeter at the quantum projection-noise limit, Phys. Rev. A 105, 022801 (2022).