Influence of camera resolution and distance in measuring structural displacements using Unmanned Aerial Vehicles for applications in bridge monitoring

Measurement errors analyzing the displacements in structures (i.e. bridges) using static camera techniques, is commonly related to camera resolution, distance between the camera and the measuring object, digitization, post-processing methods and procedures of analyzing the
displacements. In the case of using unmanned aircrafts, known as drones, stabilization becomes an issue where the frame by frame must be analyzed separately. This paper investigates the errors associated with measuring structural displacements in simply supported beams in relation to the camera resolution, field of view and digitization of the images acquired from the unmanned aircrafts. Four incremental weights were used to apply the load on the mid-span of the beam and the vertical displacements were measured using displacement sensors. In this study, a commercially available unmanned aircraft suitable for structural bridge inspections, imaging equipment and advanced image processing techniques were implemented. Accounting for stationary and hovering test measurements, tests were carried out and processed using tracking and image correlation algorithms. It is shown that the unmanned aircraft can be employed to measure the mid-span displacements with relatively high accuracy when computer vision methods are applied. This paper demonstrates the efficiency of the unmanned aircraft camera to measure the displacements at wider fields of view and a comparison of camera resolution characteristics is presented.