Field-Deployable Hybrid Gravimetry: Projecting Absolute Accuracy Across a Remote 24km$^2$ Survey via Daily Quantum Calibration

Absolute gravimeters deliver drift-free, high-precision measurements but are typically bulky and difficult to deploy, whereas relative gravimeters are lightweight and mobile but intrinsically limited by time-dependent drift. We demonstrate a hybrid quantum-enabled gravimetry approach in which an on-site atomic gravimeter provides routine, $μ$Gal-level calibration of two mobile spring gravimeters during a field survey spanning 24 km$^2$ of dense tropical terrain. The atomic reference enables high-precision, asynchronous cross-comparison of relative measurements acquired over seven days, effectively suppressing instrumental drift to a level required for demanding geophysical applications. This deployment captures regional gravity gradients with high fidelity under challenging environmental conditions, illustrating how field-operable quantum sensors can extend quantum-grade gravimetry beyond laboratory settings and serve as scalable calibration backbones for large-area, high-precision geophysical surveys in remote or logistically constrained environments.

💡 Research Summary

This paper presents a field‑deployable hybrid gravimetry methodology that combines a compact atomic (quantum) gravimeter with two mobile spring‑type relative gravimeters to achieve µGal‑level absolute accuracy over a 24 km² tropical forest area. The atomic gravimeter, housed in an air‑conditioned container and powered by a generator, operates continuously at a one‑minute sampling rate, providing a drift‑free SI‑traceable reference. Two CG6 spring gravimeters are used for spatially dense surveys, each measuring along predefined transects with stations spaced at least 50 m apart. Daily, the spring instruments are co‑located with the atomic reference during an overnight period (18:00–07:00) to record simultaneous data. By comparing the nightly spring data with the continuous atomic record, a linear drift term for each spring gravimeter is estimated and applied as a daily correction. This approach suppresses instrumental drift far more effectively than a single global calibration, capturing a gradual ~50 µGal increase observed by the atomic sensor over the eight‑day campaign.

Precise positioning is achieved through a kinematic GPS (PPK) workflow. Each spring gravimeter carries a rigid‑mount GPS antenna; a nearby fixed reference station supplies carrier‑phase data. Post‑processing yields vertical uncertainties <10 cm for 59 of 262 stations, corresponding to ~10 µGal gravity precision, while an additional 127 stations provide coarser but still useful elevation data. Elevation corrections incorporate free‑air (0.3086 mGal m⁻¹) and Bouguer (0.04193 mGal m⁻¹ · ρ) terms; terrain corrections are omitted due to limited DEM resolution, a reasonable simplification given the low relief of the survey area.

Temporal corrections also include tidal removal using the QuickTide model (amplitudes up to 150 µGal). The atomic gravimeter’s Allan deviation in the field reaches a minimum of 4 µGal, only slightly higher than laboratory values (≈2 µGal) because of environmental vibrations and tilt noise. After applying tidal, drift, and elevation corrections, the final gravity map spans –2 mGal to +3 mGal, revealing a coherent northeast–southwest gradient likely reflecting subsurface density variations.

Key insights are: (1) a portable atomic gravimeter can maintain laboratory‑grade long‑term stability in a rugged field setting; (2) daily overnight cross‑calibration reliably removes both linear and slowly varying drift components of spring gravimeters; (3) GPS‑PPK provides sufficient vertical control to anchor relative measurements to an absolute reference; and (4) the hybrid system enables high‑precision, large‑area gravity surveys in remote, logistically challenging environments. The study demonstrates that quantum‑grade sensors can serve as scalable calibration backbones, extending the reach of precision gravimetry to applications such as groundwater monitoring, crustal deformation studies, and long‑term environmental observation. Future work may integrate higher‑resolution topography, automate real‑time drift estimation, and expand the network to continuous monitoring over broader regions.