Visualizing subsurface structures with drone-based magnetic surveys — AIST successfully acquires data at Mount Aso crater

A research group led by Group Leader Ayumu Miyakawa, Technical Staff Shigeo Okuma, and Deputy Director Yoshinori Miyachi of the Research Institute of Geology and Geoinformation of AIST (National Institute of Advanced Industrial Science and Technology), has announced the successful visualization of subsurface structures in hazardous, human-inaccessible areas using drone-based aeromagnetic surveys.

During a survey of the Mount Aso crater in Kumamoto Prefecture, the group confirmed that data could be acquired with a spatial resolution more than four times higher than that of conventional helicopter-based surveys. By utilizing their proprietary 3D magnetic inversion analysis technology, they visualized the subsurface structure and identified the distribution of hydrothermal alteration zones. This achievement is expected to be applied to slope disaster risk assessment and resource exploration. The results were published in Progress in Earth and Planetary Science on March 4.

Slope disasters are caused by slope failures and occur through a combination of inherent geological factors and external triggers such as rainfall. While aerial surveys using aircraft are conducted in areas where human entry is difficult, operational costs are high. There have been high expectations for the application of drone technology, but practical examples remained limited.

In this study, the research group verified the applicability of a method combining drone-based aeromagnetic surveys with 3D magnetic inversion analysis for estimating the subsurface structure from magnetic data. The objective was to identify subsurface vulnerabilities in volcanic regions and steep slopes with high resolution.

The team selected the western slope of Mount Aso, which has a history of landslides and slope failures, as the target site. They investigated whether it was possible to identify hydrothermal alteration zones, i.e., areas where rocks become increasingly fragile due to chemical changes caused by hydrothermal fluids and volcanic gases supplied from magma reservoirs.

In hydrothermal alteration zones, magnetic minerals disappear as rocks turn into clay, resulting in localized magnetic anomalies.

To first understand the broad subsurface structure, the group re-analyzed existing data from helicopter-borne magnetic surveys. In areas where fumaroles (volcanic gas vents) and hot springs are distributed, they confirmed planar distribution of regions with weaker magnetization compared to their surroundings.

In the drone survey, conducted by suspending a magnetic sensor from the aircraft, the team succeeded in measuring at a density four times higher than conventional methods, with a flight altitude of under 100 meters and a line spacing of less than 25 meters.

By applying a 3D magnetic inversion analysis, it was revealed that a significantly low magnetization area extends horizontally and continuously in the depth direction from the surface to several tens of meters in depth. This confirmed that highly vulnerable, clay-rich areas caused by hydrothermal alteration can be accurately mapped.

Journal Information
Publication: Progress in Earth and Planetary Science
Title: UAV-based magnetic survey for detecting hydrothermal alteration zones relevant to landslides: A case study at Aso Volcano, Japan
DOI: 10.1186/s40645-026-00800-3