Review of the Drone Applications in Urban Underground Environments

The rapid urbanization of modern cities has intensified the demand for innovative solutions to inspect, maintain, and map complex underground infrastructure, including tunnels, sewers, and utility networks. While drones have revolutionized aerial applications, their potential in GPS-denied, confined underground environments remains underexplored and warrants systematic analysis. This review paper synthesizes advancements, challenges, and opportunities in deploying drones for urban underground applications through a rigorous systematic literature review. Key findings highlight transformative use cases in infrastructure inspection, disaster response, and 3D LiDAR mapping for integration with urban digital twins. Critical technical challenges—such as sensor degradation in high-humidity environments, adaptive SLAM algorithms for GPS-denied navigation, and limited battery autonomy—are analyzed alongside emerging solutions like tethered power systems and edge-AI for real-time data processing. The study further identifies regulatory gaps in underground airspace governance and interoperability barriers between drone-collected data and urban planning tools. Future directions emphasize swarm robotics for scalable exploration, hydrogen fuel cells for extended missions, and policy frameworks to standardize safety protocols. By bridging robotics, civil engineering, and urban planning disciplines, this review provides a roadmap for researchers and practitioners to advance drone technologies while addressing societal needs for safer, cost-effective, and sustainable urban underground management.