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Inspection of deep tunnel networks is extremely challenging due to their inaccessibility, and them being an unknown and potentially hazardous environment. Unmanned aerial vehicles (UAVs) provide a viable alternative for access, and are unaffected by debris or sewer flow. However, commercial UAVs are designed for high altitude aerial imagery and are not appropriate for short-range detailed imaging of tunnel surfaces. In addition, autonomous flight is usually achieved using GPS, which is not available underground. This paper presents the design and development of a smart UAV platform, Surveyor with Intelligent Rotating Lens (SWIRL), customized for autonomous operation in tunnels. It can capture high resolution images for subsequent image processing, and defect detection and classification. An innovative rotating system enables undistorted imaging of the tunnel's inner circumference surface using a single camera. The proposed location method using limited data resulted in substantial unit weight and power consumption reductions, compared to existing systems, making more than 35 minutes of autonomous flight possible.

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