## 1 Introduction  
Global extreme climatic events such as hurricanes, floods, and heat waves present significant challenges to both human life and the economy. The monitoring of water levels and the structural integrity of critical public facilities and infrastructure is essential for the prevention and mitigation of such disasters. Fiber optic sensors are particularly advantageous as they are power-free, compact in design, possess long operational lifespans, and are resistant to electromagnetic interference [1]. Additionally, they are highly sensitive and capable of measuring a wide range of physical parameters [2, 3, 4, 5]. These characteristics render fiber optic sensors an optimal choice for monitoring efforts toward achieving net-zero carbon emissions. Recent advancements in fiber optic sensors for liquid level or hydrological-related measurement have garnered significant attention [6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20], attributed to their numerous advantages. However, existing research predominantly addresses the measurement of a singular liquid level parameter. In practical applications, variables such as the liquid's refractive index, temperature fluctuations, or the inclination of the monitoring structure may compromise this focus. Fiber optic interferometer sensors exhibit excellent measurement resolution, wide-band measurability [21, 22, 23, 24], and the capacity to assess multiple parameters [25, 26, 27] simultaneously. However, due to the inherent complexity of the spectrum, employing multiple fiber optic interferometer sensors for concurrent measurements can often present significant challenges. Distributed fiber optic sensors possess the capability to measure multiple sites and various parameters simultaneously at a single location [28, 29, 30, 31]. However, it is important to note that these sensors are typically more expensive and may not provide a cost-effective solution for measurements over small areas. Standard FBG sensors can be configured in arrays to provide measurements akin to those obtained through distributed fiber optic sensing and can be effectively integrated with FSO to address cable routing challenges [32, 33]. When FSO technology is integrated with sensors in applications where optical communication over distances of several hundred meters is feasible [34, 35]. Commercially available FSO systems can achieve ranges of several kilometers or more, demonstrating their capability to function effectively even under adverse weather conditions [36]. This resilience highlights the utility of FSO technology in a diverse range of applications requiring reliable data transmission across considerable distances. The liquid level measurement technique founded on the Archimedean buoyancy principle enables FBG sensors to accurately gauge liquid levels through a stretching mechanism [6]. This approach circumvents the influence of refractive index variations that may occur when the sensor comes into contact with the liquid [6]. Furthermore, intensity-based measurement sensors are often susceptible to variations in light source power; in contrast, FBG-based sensors exhibit resilience to such fluctuations [6]. By utilizing the center wavelength of the FBG sensor as a reference point, a single FBG is capable of simultaneously measuring both vibration and temperature [37]. However, simultaneous measurement of strain and temperature is not feasible unless spectral interrogation techniques are implemented in lieu of relying solely on the center wavelength value of the FBG [38]. In Archimedean buoyancy principle-based FBG subsidence sensor applications, two physical quantities, specifically changes in water level and tilt, are measured through the degree of stretching of the FBG indicated by the center wavelength. Consequently, the main limitation of FBG sensor measurements is that additional sensors must be arranged to measure more than two physical quantities simultaneously, owing to the same mechanism for FBG spectrum variation of these quantities.