# FBG-Based Monitoring of Geohazards: Current Status and Trends
## 5 Challenges and Future Trends  
Various research has proved the feasibility and reliability of FBG sensing systems for field monitoring of geohazards. However, we should know the FBG sensors are not universally effective. First, the FBG sensors can only perform quasi-distributed monitoring and the sensor number in series is limited. Fully distributed sensing technologies, such as BOTDR and Rayleigh backscattering optical frequency domain reflectometry (OFDR) have advantages over FBG in measured length and the amount of information. Hence, these technologies are employed mostly for long-distance and large-magnitude monitoring of geohazards which allows for low measurement accuracy and frequency. Comparatively, FBG is more suitable to be incorporated into geotechnical instrumentation such as an inclinometer for accurate and real-time measurement. On the other hand, the cost of an FBG system is still higher than conventional ones [83]. For instance, the prices of an interrogator and a FBG sensor are about \(\ell 20\),\(000\) and \(\ell 50\)-\(300\), respectively. But it is predictable that once the FBG system becomes common practice, the cost will decrease significantly [4]. In general, FBG and conventional sensor systems, especially the remote monitoring systems, are complementary and both approaches are of interest. The field performance of FBG sensors should be validated using conventional ones. However, only a few cases of integrated monitoring of geohazards using both technologies have been reported before. Advanced monitoring methods, appropriate layout of different types of sensors, and a smart warning system are needed for practical monitoring and prediction of geohazards such as landslides. Based on the above review, we propose that the following seven trends in FBG-based geohazards monitoring will be realized in the future. 1. Development of cost-effective fiber optic demodulation and integration technique. For field applications, rugged and portable devices with low power consumption are desired, so that continuous measurements can be conducted in all-weather conditions. In the future, the solar energy power supply system and general packet radio service (GPRS)-based wireless data transmission will be used to establish the next-generation remote and unattended monitoring system. Monitoring data will be directly transmitted to host computers and then uploaded on websites accessible to interested parties. In addition, hundreds of FBG sensors will be multiplexed in series along a fiber using new demodulation techniques;
2. Development of innovative sensors for capturing three-dimensional strain and stress states in complicated geological structures, e.g., soil strain rosettes and total stress cells. Because extreme conditions may be encountered during monitoring, robust sensors for large deformation, high temperature and pressure measurements will be developed. Most importantly, these sensors should be correctly calibrated prior to operation;
3. Development of self-temperature compensation method. Using special algorithm, the discrimination of temperature and strain effect can be obtained. Alternatively, the Bragg wavelength shift will not be influenced by temperature change with the help of new sensor design;
4. Development of convenient packaging and protection methods. For instance, adaptive materials such as basalt fiber-reinforced polymers can be used. One advantage of this material is that such polymers are made from natural basalt rocks. Using special sensor packaging methods, the increase or decrease of measurement sensitivity can be achieved;
5. Realization of real-time process, error analysis and abnormality recognition of huge monitoring data. A smart monitoring system should have a powerful data management subsystem with the functions of automated visualization, self-diagnosis, and self-repair. To efficiently process and interpret the huge data retrieved from FBG sensors, the integration of the techniques of big data digging and internet of things is preferred.