Measuring Transverse Displacements Using Unmanned Aerial Systems Laser Doppler Vibrometer (UAS-LDV): Development and Field Validation

Abstract

Measurement of bridge displacements is important for ensuring the safe operation of railway bridges. Traditionally, contact sensors such as Linear Variable Displacement Transducers (LVDT) and accelerometers have been used to measure the displacement of the railway bridges. However, these sensors need significant effort in installation and maintenance. Therefore, railroad management agencies are interested in new means to measure bridge displacements. This research focuses on mounting Laser Doppler Vibrometer (LDV) on an Unmanned Aerial System (UAS) to enable contact-free transverse dynamic displacement of railroad bridges. Researchers conducted three field tests by flying the Unmanned Aerial Systems Laser Doppler Vibrometer (UAS-LDV) 1.5 m away from the ground and measured the displacement of a moving target at various distances. The accuracy of the UAS-LDV measurements was compared to the Linear Variable Differential Transducer (LVDT) measurements. The results of the three field tests showed that the proposed system could measure non-contact, reference-free dynamic displacement with an average peak and root mean square (RMS) error for the three experiments of 10% and 8% compared to LVDT, respectively. Such errors are acceptable for field measurements in railroads, as the interest prior to bridge monitoring implementation of a new approach is to demonstrate similar success for different flights, as reported in the three results. This study also identified barriers for industrial adoption of this technology and proposed operational development practices for both technical and cost-effective implementation.

A Speech Enhancement Algorithm for Speech Reconstruction Based on Laser Speckle Images

“…In the field of information security and the prevention of social crimes, covertly acquiring clear remote speech signals has become an important research topic [ 1 , 2 ]. For years, researchers have proposed a variety of methods for measuring vibration signals [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ], many of which are used in speech signal reconstruction and are based on laser. There are two main methods based on remote vibration signals detection: one is based on laser Doppler vibrometer (LDV) [ 3 , 4 , 5 , 6 , 7 , 8 ] and the other is optical sensing and image processing technologies [ 9 , 10 , 11 ].…”

UAV-based inspection of bridge and tunnel structures: an application review

“…Another emerging imaging-based application with UAVs is the displacement/deformation measurement techniques of bridge structure, e.g., photogrammetric computer vision [9], [83], [89], [97], [146] and digital image correlation (DIC) [79], [92]- [95], [148]. Despite these imaging-based techniques, it is also worth mentioning the use of Laser Doppler Vibrometers (LDV) in UAVs as a non-contact sensor to measure bridge displacements [84]- [86].…”

Miniaturization of Laser Doppler Vibrometers—A Review

“…For example, in physiology, the continuous detection of the eardrums is needed to assist hearing abilities, which requires a very compact LDV sensor to be installed in the ear canal. In structural health monitoring applications, a miniaturized LDV would enable a sensing system carried by a mobile device such as a drone that can reach locations that are not easily accessible (e.g., middle of a long-span bridge) [33]. Therefore, a lightweight and compact LDV sensor is required to meet the payload requirements of drones.…”