## 3 Experiment Results and Discussions
### Turbidity Sensing
We collected eight measurement samples in Lake Koyamaike, and the places are indicated in Figure 7. Sample Nos. 3 and 4, and Nos. 5 and 6 were collected at the same place, but Sample Nos. 4 and 6 were collected after a pause. In the measurement, we measured the photovoltage for each sample, and it was converted to NTU turbidity using the relationship shown in Figure 6. The NTU turbidity measurement results are summarized in Figure 8. The photovoltage measurements were performed by PD1 and PD3, and the results were in agreement. The turbidity of Sample Nos. 4 and 5 are relatively higher than the others due to the muddiness of the stream during sampling. Figure 5: The measurement results for the calibration solutions of kaolin shown in Figure 3.0 PDI is placed perpendicular to LED1, and PD3 is placed at the bottom of the sample. Figure 3.1 The measurement results by the commercial turbidity sensor for the same kaolin calibration solutions used in the measurement by the measurement setup in Figure 3.2 The photovoltage values can be converted to an NTU value. We also performed calibration with the St-DVB copolymer microbeads solutions for comparison. For calibration solutions of St-DVB copolymer microbeads, we prepared eight different concentration calibration solutions. The prepared St-DVB copolymer microbeads solution concentrations were 0, 1, 2, 5, 10, 20, 50, and 100 mg/L and are shown in Figure 3.3 In the measurement, the measurement setup and procedure were the same as that used for the kaolin calibration solutions. The measurement results are shown in Figure 3.4 Here, we only measured the photovoltages from PD1 and PD3. With the St-DVB copolymer microbeads calibration solution, we were also able to distinguish the degrees of turbidity according to the measured photovoltages. Moreover, we were able to successfully confirm the linear relationship between the concentration of the calibration solution and the scattered light intensity. Although the measurement results between PD1 and PD3 have small differences, we could obtain linearity with almost identical slopes. This means that the St-DVB copolymer microbeads are uniformly distributed in the solution and the precipitation effect can be ignored. The zero calibration is also necessary only to consider the scattered light intensity when we measure the turbidity of the environmental water sample. Figure 3.5 Turbidity measurement results for samples at the 8 places indicated in Figure 3.6  
Figure 3.7 Sampling position at Lake Koyamaike in Tottori Prefecture, Japan. We collected 8 environmental water samples from Lake Koyamaike. Figure 3.8 The 8 different concentration calibration solutions of St-DVB copolymer microbeads: From left to right, the concentrations are 100, 50, 20, 10, 5, 2, 1, and 0 mg/L. We also performed turbidity measurements with the same environmental water samples, which were used in previous turbidity measurements. The measurement results based on the St-DVB copolymer microbeads solution calibration are shown in Figure 3.9 The NTU turbidity conversion was performed by using the relationship shown in Figure 6 as well. The turbidity values measured by PD1 agreed with those measured by PD3. Although the obtained turbidity values based on the St-DVB copolymer microbeads solution calibration were slightly smaller than those based on kaolin solution calibration. Specifically, in most low turbidity areas, the turbidity showed almost the same values. According to the measurement results for each calibration solution shown in Figures 5 and 10, the St-DVB copolymer microbeads solution calibration is considered as the more accurate method. However, in real applications, it is more important and meaningful to detect and clarify low turbidity water instead of high turbidity water. Therefore, the cheaper and easier method using the kaolin calibration solution is considered to be the effective one.