DLR is developing new structural health monitoring approaches for large engineering structures using drones as a part of a DFG funded project, Flyable Mirrors (project website: https://www.dlr.de/ft/en/desktopdefault.aspx/tabid-1360/1856_read-76419). The project aimed at enhancing the dynamic characterization of the large civil structures by developing a novel airborne laser Doppler vibrometer (LDV). The LDV system consists of a commercial laser LDV mounted on a motorized pan/tilt stage on the ground, an optical beam steering unit (e.g. a reflective mirror) carried by a multi-rotor drone and a central control unit. A laser beam is emitted from the LDV toward the drone’s mirror. The drone’s mirror provides an additional steering control for said laser beam to reach a certain point at a target structure. The reflected beam is then directed back to the LDV via the same path. The Doppler shift between the emitted and the reflected laser beams is used to measure the vibration activity of the structure and to evaluate its material strength and health. 

A key challenge is related to a precise real-time position measurement for the drone’s mirror using a camera attached to the LDV unit. This measurement is necessary for adjusting the motorized pan/tilt stage of the LDV unit to keep the laser beam at the center point of the mirror. This task will be implemented by vision-based position tracking algorithm using Python program in an embedded platform.