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

TL;DR

The paper addresses drift in relative gravimeters during large-area geophysical surveys and proposes a field-deployed hybrid gravimetry approach that uses a containerized atomic gravimeter as an on-site absolute reference to calibrate mobile relative gravimeters. Demonstrated over a 24 km^2 tropical terrain, the method achieves daily calibration and centimeter-level elevation control via GPS-PPK, with drift suppressed to the microgal level (Allan deviation minima of $4\,μ\text{Gal}$) and a slow ocean-loading–driven baseline drift of $50\,μ\text{Gal}$. The approach yields a gravity map spanning roughly $-2$ to $+3$ mGal and reveals a coherent NE-SW gradient, validating cross-day stability and spatial fidelity despite environmental challenges. This work shows that field-ready quantum sensors can provide scalable calibration backbones for high-precision gravity surveys in remote or logistically constrained environments, with broad potential applications in hydrology, crustal dynamics, resource prospecting, and environmental monitoring.

Abstract

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.

Figures (4)

• Figure 1: Layout of the reference station used for daily calibration. The atomic gravimeter was housed inside an air-conditioned container (approximately 75 cm $\times$ 75 cm $\times$ 200 cm) and operated continuously to provide an absolute gravity reference, with the container positioned on a cemented clearing to ensure stability. Spring gravimeters were placed in a neighbouring weather-proof metal enclosure during overnight calibration periods, enabling correction for instrumental drift. A common generator provided electrical power throughout the survey.
• Figure 2: Overnight calibration data for the two spring gravimeters, $g_\text{sgA}$ (a) and $g_\text{sgB}$ (b), compared against continuous absolute gravity measurements from the atomic gravimeter $g_\text{ag}$ (c), collected over eight days. Each spring gravimeter panel shows uncorrected data (red), a single global drift correction from the start of the survey (blue), and daily drift corrections derived from the atomic reference (green). All data are tide-corrected and plotted as relative gravity to emphasize temporal variations. The daily calibration accurately tracks the gradual 50µ increase observed by the atomic gravimeter, while the single global correction does not. A brief discontinuity in $g_\text{sgB}$ near the end of the survey resulted from a power interruption and was corrected during processing. Panel (d) shows the Allan deviation of the atomic gravimeter measurements in the field (circles) compared with laboratory data over a similar timescale (squares), demonstrating comparable long-term stability with slightly elevated white-noise levels in the field due to environmental vibrations and tilt.
• Figure 3: Field gravity measurements colored by PPK solution quality. Green points correspond to fully converged solutions with $<$10 cm vertical uncertainty. Blue points indicate partially converged solutions that provided usable elevation estimates despite larger or less well-defined uncertainties. Orange points mark locations where the PPK algorithm did not produce a usable solution; these stations were excluded from elevation-dependent analyses.
• Figure 4: Top: Gravity distribution across the survey after applying temporal and elevation corrections to all stations with a usable PPK solution. Bottom: Gravity measurements along the reference path with corresponding high-precision elevation data. Distance 0 corresponds to the westernmost point of the path; upon reaching the junction, the path follows a counterclockwise loop before continuing east. Markers indicate the specific instrument (triangle: spring gravimeter A; square: spring gravimeter B), and colors correspond to the survey day. The profile demonstrates temporal consistency across repeated measurements and reveals a gradual gradient along the path.