Measuring Vibrations in Large Structures with Laser-Doppler Vibrometry and Unmanned Aerial Systems: A Review and Outlook

Vibrations in large structures such as buildings, dams, cranes, plants, drilling platforms, bridges, and wind turbines are often difficult to measure because, among other reasons, it is challenging or even impossible to attach suitable vibration sensors to all the positions/locations of interest. Optical, noncontact measurements from the ground, conversely, are only possible for the visibly accessible parts and often require long measurement distances or unfavorable viewing angles from the ground due to the vertical extent of the location of interest on the large structure. Employing noncontact vibration measurement methods from or via an unmanned aerial vehicle (UAV) is preferable for many applications and is, therefore, becoming an increasingly interesting research topic around the world. This paper reviews the current state of the art for measuring and analyzing vibration in large structures with laser-Doppler vibrometry (LDVy) supported by unmanned aerial systems (UASs)—which employ one or more UAVs and associated ground-based control equipment—and related topics, including excitation as well as data collection, transfer, processing, and interpretation. The review includes a brief overview of vibration-determined damage detection in large mechanical and civil structures, associated nondestructive testing (NDT) sensor technologies including in particular LDVy, UAV technology, and other NDT measurements supported by UASs with a focus on LDVy as the preferred vibration sensor technology. Ultimately, following the presentation of the state of the art, we discuss some of the currently foreseen challenges for implementing LDVy with UASs for operational stability analysis of large structures and the currently addressed and possible future research topics required to maximize the benefit of this exciting system integration opportunity.