InSAR Coupled with UAV-Based Infrared Thermography in the Context of Bridge Monitoring

Examination of deformations in bridges is an important source of information in terms of giving an idea about the health status of bridges. Bridges are often exposed to more than one external force, the vibrations caused by the forces they are exposed to can affect the quality of use of the bridge and its safety during use of the structure. Reliable description of the behavior of the bridge under load requires the use of a method that allows simultaneous observation of many points. Therefore, the measurement technique of these forces that bridges are exposed to must provide with high accuracy and high frequency displacement observation. It is also desirable that the measuring device does not need to have direct access to the observed object. For these reasons, this project offers the opportunity to evaluate the health status of bridges by matching the data obtained by satellite-based Interferometric Synthetic-aperture Radar (InSAR) technique on three-dimensional models via Unmanned Aerial Vehicle (UAV) images. The InSAR technique enables the detection of deformations occurring on the earth with millimeter precision by using Synthetic-aperture Radar (SAR) data collected by radar satellites in earth orbit. Sentinel-1A and Sentinel-1B satellites, which are currently in orbit, offer both detection and continuous observation over large areas, since their data is made public by the European Space Agency (ESA) and data is collected by passing through the same region every six days. In this way, deformations occurring on the bridge can be evaluated periodically to detect abnormal displacements at any position of the bridge. For this purpose, it was aimed to use two independent Sentinel-1 SAR datasets covering the years 2016-2021, containing 240 images in ascending orbit and 169 images in descending orbit, respectively. With the deformation maps created from these time series, the displacements on the bridges were determined in a short time and at low cost. These displacements were visualized by integrating them into the three-dimensional infrared - thermography (IRT) model obtained from the UAV images.