Deep-Penetrating UAV-GPR Imaging for Inapparent Landslide Investigation in Rugged Terrain

An inapparent landslide refers to a subsurface mass movement that develops without producing obvious surface deformation or destruction . Such landslides commonly occur within rock or soil masses that are highly susceptible to fracturing and possess inherently weak internal structures. When triggered by external factors such as rainfall, these concealed landslides can accelerate and expand rapidly, causing abrupt changes in topography and resulting in severe losses of life and property. Crucially, recent studies have identified the bedrock interface as the decisive factor for the stability analysis and early warning of such landslides. However, conventional ground-based monitoring methods provide only sparse point measurements and fail to resolve the continuous subsurface structure.

Unmanned Aerial Vehicle-based Ground-Penetrating Radar (UAV-based GPR) is an efficient and non-destructive geophysical detection technology. It generally consists of the UAV platform, a GPR subsystem, the flight control and basic positioning sensors of the UAV, high-accuracy positioning sensors, and a communications subsystem (Figure 1). Compared to conventional ground-based GPR, UAV-based GPR offers offers a promising non-contact solution for such landslides, enabling rapid and safe surveys over hazardous terrain Nevertheless, in complex mountainous environments, dense vegetation and steep, undulating topography significantly degrade data quality, leading to severe imaging artifacts and interpretation ambiguity .

In this study, we propose reverse time migration (RTM) formulated in a curvilinear coordinate system for UAV-based GPR. Subsequently, we introduce an interface extraction technique to accurately identify the continuous bedrock interface from the migration profiles. For data acquisition, we deploy a low-frequency UAV-based Stepped‑Frequency Continuous‑Wave GPR (SFCW-GPR) system in the landslide-prone regions of Sichuan Province. The system achieves effective penetration depths of up to 20 m while maintaining stable imaging quality. These results indicate that the proposed framework provides a practical and high-resolution solution for the identification and structural characterization of inapparent landslides in complex mountainous environments.

Figure 1 The UAV-based GPR system used for landslide investigation.