Limitations of OFDR measurements in civil structural health monitoring

In order to assure the structural health of civil infrastructures, distributed fiber optic sensing (DFOS) is often used and optical frequency domain reflectometry (OFDR) measurements are a potential candidate for long-term monitoring. From these measurements, information about the structure’s state and its behavior are gathered. A very important aspect of long-term monitoring is the link to the zero measurement in order to be able to determine changes. There are multiple reasons, why the linkage of measurements is not possible, like the wavelength range of the interrogators, broken sensors, vibrations during the measurement, wrong signal termination at the sensor, change of the interrogator and large static or dynamic strain changes. These limitations present challenges for long-term monitoring of civil structures. Our investigation showed that different OFDR interrogators have different limitations and that solving the challenges imposed is not always possible. A knowledge of these limitations is crucial to design a functioning long-term monitoring setup.