## 3 Experimental Results
The water temperatures in Figure 3 correspond to 30 \({}^{\circ}\)C, 40 \({}^{\circ}\)C, 50 \({}^{\circ}\)C, and 60 \({}^{\circ}\)C in Figure 3a-d and the water level and inclination settings are consistent with those in Figure 2. The data presented in Figure 3 indicate that, irrespective of water temperature, an increase in water level results in a corresponding reduction in wavelength. This phenomenon can be attributed to the amplification of buoyancy, which consequently decreases the strain experienced by the FBG. In addition, 1542 nm of the FBG2 wavelength is placed on the right side of TB, so TB tilted to the right will cause the water level to rise, i.e., buoyancy willincrease so that the FBG wavelength will drift towards the shorter wavelengths, while TB tilted to the left will have the opposite effect. Corresponding to the results in Figure 2, the wavelength drift is linear with respect to the angle of inclination. Furthermore, an increase in water temperature is observed to cause a significant drift of the FBG wavelength towards longer wavelengths. As the temperature of the water rises, the buoyancy typically declines due to a decrease in water density. Consequently, if the buoy volume of discharged water remains constant, the overall buoyancy of the water will diminish. Figure 3: The FBG wavelength shift results of the tilt measurements correspond to 1542 nm at different water levels. The temperature conditions for the water during the measurements were as follows: (**a**) 30 \({}^{\circ}\)C, (**b**) 40 \({}^{\circ}\)C, (**c**) 50 \({}^{\circ}\)C, and (**d**) 60 \({}^{\circ}\)C.  
Figure 2: At varying water levels, FBG subsidence sensors have been deployed at both skewed positions (represented by solid line data) and standard positions (denoted by dashed line data) to monitor the wavelength drift resulting from tilting. The measurements correspond to the 30 \({}^{\circ}\)C water temperature with the following water levels: (**a**) 1 cm, (**b**) 1.5 cm, (**c**) 2 cm, (**d**) 2.5 cm, (**e**) 3 cm, and (**f**) 3.5 cm. As previously noted, the necessity of concurrently measuring water levels and incline variations necessitates the deployment of two FBGs. This requirement arises because the right-leaning condition observed at low water levels may yield wavelength readings for the FBGs that are indistinguishable from those generated under the left-leaning condition at elevated water levels, as illustrated in Figure 3. Consequently, employing two FBGs for measurements can effectively eliminate potential confusion regarding the parameter signals and address this limitation. Figure 4a-d illustrate the wavelength measurements of FBG1, which is based on a reference wavelength of 1548 nm. The measurement setups utilized are identical to those presented in Figure 3a-d. A notable distinction is that FBG1 is positioned on the left side of the TB. Consequently, when the TB is inclined to the left or right, the resulting changes in the water level exhibit an inverse relationship with those observed in FBG2. Therefore, the most significant finding depicted in Figure 4 is that the drift tendency of the FBG wavelength is precisely opposite to that illustrated in Figure 3. By recording the wavelength readings from both FBG1 and FBG2, it is possible to concurrently ascertain the water level and tilt parameters. The findings presented in Figures 3 and 4 indicate that an increase in temperature results in a drift of the FBG towards longer wavelengths. However, while measuring both water level and tilt using two separate FBG sensors is feasible, conducting concurrent measurements of water temperature with the same two FBGs poses significant challenges. This difficulty arises from the fact that the wavelength drift of the FBG, attributed to buoyancy changes stemming from variations in water temperature, is minimal. Furthermore, a more complex consideration is that the salinity of the water influences its density, subsequently affecting buoyancy.