# A Data-Driven Intermittent Online Coverage Path Planning Method for AUV-Based Bathymetric Mapping
## 4 Experimental Validation in Simulated Environments
### Results
Thus, we choose the lawnmower path with 42 m inter-distance as the reference when evaluating the proposed method. According to Figure 10, most results of the proposed method have advantages over the lawnmower result (42 m inter-distance) when the coverage rate is under 90%, indicating that the proposed method has high coverage efficiency at most of mission time. Meanwhile, the run #2 reaches  
Figure 9: Simulation results of a lawnmower path (**left one**) and a spiral path (**right one**). For the former, the inter-distance between the transects is 42 m. For the latter, the inter-distance between the zonal transects is 46 m, and the inter-distance between the meridional transects is 33 m.  
99% coverage rate much faster than the lawnmower method, indicating that if the weights are adjusted properly, the proposed method can have advantages over lawnmower method on coverage efficiency during every stage of a mission. Moreover, the runs with zero \(W_{e}\) result in relatively higher coverage efficiency compared to the other runs, revealing that pursuing global coverage in early stage (when \(W_{e}\) is not 0) will have a trade-off in coverage efficiency in the long run, anyhow, in a limited range. Figure 11 shows the comparison of the overall confidences of the maps obtained from different simulation runs. The overall confidence of a map is defined as the average confidence of the cells in the workspace, and is represented by the height of the corresponding bar in the figure. The confidence of each cell is obtained by Equation (10). The color layers indicate different runtime bands, 0 to 3000 s (orange), 3000 s to 6000 s(yellow), 6000 s to the final runtime labeled on the top of each bar (green). As shown in the figure, for lawnmower paths and spiral paths, the resultant confidence is closely related the inter-distance. A wider inter-distance leads to higher confidences in the early stages (3000 s runtime and 6000 s runtime), but a lower final confidence. In contrast, the resultant confidence from the runs with the proposed method has a more consistent value as high as 0.98. More importantly, these runs also show a higher confidence at early stage in orange and yellow layers. Since the above trials are all based on the same terrain shown in Figure 2, we continue to verify the performance of the proposed method in different terrain models. The coverage goal is again set at  
Figure 11: Confidence comparison of different strategies and parameters. The confidence refers to the average confidence of the cells in the workspace. Figure 10: Coverage capabilities of different strategies and parameters. 99%. Figure 12 shows the results on different terrains with the same objective weights of run #2 in Table 2. The terrain in the left picture of Figure 12 is generated using the same function but different elevation settings, while the terrain on the right is an actual topography from the bathymetric data of Narragansett Bay, Rhode Island, USA, provided in [33]. In both trials, we kept the vehicle moving at a similar altitude as the trials shown in Table 2, and the workspace size was set to be the same. The total traveling distances in the two terrains are 8368 m and 7371 m, respectively, which are shorter than the lawnmower path shown in Figure 6:0 These results indicate the proposed CPP method has a consistent performance on different terrain models.