## 3 Results  
### Data Analysis  
Of the 26 flights realized, those flown at a height of 30 m were chosen for the study comparison. From observing the 30 m and 50 m flights, we determined that the lower resolution of the 50 m flights affected the visualization of the data and point clouds. The point clouds obtained from the thirteen 30 m flights were compared against those of the survey conducted with conventional instruments [69]. The differences found in the finished floor levels (FFL) of the steps and the bottom of the pool were used to calculate the vertical error. Figure 8 provides four examples of point clouds, wherein the red lines represent the levels obtained using a UAV and the blue lines represent the levels obtained from conventional topographic surveys. The figure shows the distortion in the point clouds for flights 11, 15, 19, and 23. The examples correspond to flights made at a height of 30 m. The point cloud from flight 11 was obtained from a pool without water and serves as a reference of the surface without distortion. Figure 8: Comparison between the point clouds obtained using a UAV and those obtained from conventional topographic surveys. Since the luminosity and temperature of the remaining three flights are similar, it is easy to observe how the turbidity has changed. In these examples, the point clouds do not faithfully represent the depth of the pool. Even as the depth increases, the distortion of the point clouds increases, and the accuracy of the distances between the measured levels decreases. Flight 23 shows an extreme distortion of the point cloud, which presented levels of 47.41 NTU on average, the highest level recorded in the experiment. This result is consistent with the observations of other studies [15; 29] in which the turbidity of the water directly influenced the variations in the results obtained from data collected using UVAs. This study's high degree of innovation is worth noting, as it simulates a controlled environment. It is assumed that studies in uncontrolled environments involving water resources can be very variable and result in a high variation in errors during data collection with UVAs. Charts were generated where the relationships between the errors obtained in the bathymetric surveys were assessed at different pool depths. The variables of depth, lux, and NTU (turbidity) were the most affected during the flight surveys. On the other hand, the wind speed and the temperature did not influence the errors since they did not vary significantly during the flights. Figure 9 presents an assessment of the errors found at different depths, considering the variation in luminosity and turbidity during the surveys. The errors found in each flight with a water-filled pool were grouped. The bars represent the luminosity level (in lux) recorded during each flight, the orange line indicates the turbidity (in NTU), and the gray line denotes the error at each depth. For example, at a constant turbidity of 4 NTU, an almost constant error is presented at each depth up to the highest luminosity, recorded at 0.73 m, which generated the highest error. Likewise, at a continuous turbidity of 21 NTU, there was a constant error up to a depth of 1.20 m, at which point the luminosity was relatively high even if it was not the highest recorded. On the other hand, when the turbidity changed from 21 NTU to 47 NTU, the error increased and the high turbidity did not allow the recording of the values for the last flight, even with a low luminosity. According to these relationships [30], it is understood that water surfaces with greater turbidity are more challenging to study with photogrammetry. Because of the refraction of light, a correction must be made due to the change in medium (air-water). Considering [PERSON]'s law [70] and the coefficients n1 = 1 for air and n2 = 1.33 for water, it was found that the equation provides a real solution if the height difference is greater than or equal to 0.236 m. The heights obtained in this case study were smaller than those obtained in many other case studies.