Flyable Mirror: Airborne laser Doppler vibrometer for large engineering structures

Large engineering structures are subjected to extreme loads that may lead to early damage and hazards for the national economy and public safety. The laser Doppler vibrometer (LDV) has been widely used for conducting ambient vibration testing (AVT) of large structures, such as towers and historical buildings. Its superior sensitivity and the possibility to measure at hard-to-reach locations make it a versatile tool. However, two challenges limit LDV performance significantly for AVTs of large structures: (a) optically inaccessible surfaces in which the LDV beam cannot reach the spot or the beam has a flat incline; and (b) significant optical deficiencies in long-range measurements due to air turbulence and laser speckle effects. In this paper, we report the development progress of a new LDV-based measurement system, Flyable Mirror. This system consists of a commercial LDV with novel noise suppression means at the ground and an optical beam steering unit (a mirror) carried by an unmanned aerial vehicle. Several preliminary experiments were conducted to build and test the first airborne LDV. Flyable Mirror will enable new insights into monitoring structural-aging mechanisms for which ground-mounted LDVs cannot be used.