# Image-Based Structural Health Monitoring: A Systematic Review
## 4 Discussion
### Purpose and Applications of Image-Based Structural Health Monitoring
#### 4.1.2 To Measure and Monitor  
SHM has the potential to become an important instrument in the field of civil engineering [7]. A proper monitoring approach enables the long-term assessment of structural performance, maintenance planning, and occupant safety [7]. A standard health-monitoring system is comprised of a network of sensors that monitor factors related to the structure and its environment's condition. Many of these factors may be monitored with standard sensors based on mechanical and/or electrical transducers. Fiber-optic sensors have made a modest but substantial debut in the sensor scene during the last few years. When compared to more established conventional sensors, fiber-optic sensors provide superior performance. Higher measurement quality, increased reliability, the ability to replace manual readings and subjective judgment with automatic evaluations, faster installation and maintenance, and a lower lifetime cost, are all examples of added value. Fiber-optic sensing technology is classified according to the measurement principle [54] and among them is the SOFO interferometric sensors made up of a pair of single-mode fibers that are inserted in the structure being monitored. The measuring fiber is mechanically linked to the existing structure (connected at both ends and prestressed in between), whilst the reference fiber is placed loose in the same pipe, which was illustrated by [54]. All structural deformations will thus result in a change in the length difference between these two fibers [54].  
Long-gauge fiber-optic SOFO sensors can monitor temperature and strain changes in concrete columns and steel link-bridge components. Fiberoptic SOFO sensors use low-coherence interferometry to function. As employed by [7], a monitoring strategy allowed the extraction of the local and global behavior of the Pinnacle@Duxton. All seven buildings and four of the 12 bridges have long-gauge fiberoptic strain sensors. During construction, building sensors were embedded in the first-floor concrete columns, and sensing data was accessible from the start of construction until the end of the structure's operational life. Bridge sensors were mounted on the bridge's surface shortly after it was built and continue to provide data throughout its operational life. This setup enabled the assessment of the long-term behavior of structures on a local and global scale. SHM has the potential to become a key instrument in civil engineering. A reliable monitoring method enables one to analyze long-term structural behavior, plan maintenance, and assure occupant safety [7]. The fiber-optic SOFO sensor and systems can be integrated to monitor dams [55], subterranean structures [56], and tunnels [57]. A schematic diagram of the SOFO system can be accessed from here [57].  
In addition to measuring and monitoring purposes, a pedestrian bridge's displacement may be tracked using 3D digital picture correlation (DIC) [58]. A pedestrian bridge subjected to static stresses is predicted to deflect, which can be observed using cameras mounted in windows of an adjacent building. CV reduces the subjectivity and error inherent in traditional SHM. SHM can be performed with minimum interruption to the environment and the structure itself thanks to CV. The detection of displacement is critical, especially for constructions that will be used for an extended period. By integrating CV and knowledge of the structure's behavior under certain conditions, monitoring the displacement of a pedestrian bridge is a realistic undertaking, but it does not limit to bridgesonly, since the 3D DIC measuring approach may also be used to monitor the behavior of other structures and their parts.