# Deep-Sea Underwater Cooperative Operation of
## 5 Work Efficiency Analysis
### Typical Operating Task  
For the above three operational modes, the elapsed time of the cooperative operation based on the lander mode and the USV mode is similar. However in certain typical operational scenarios, there is still a substantial difference in completing fixed investigation tasks. Consider an example in which an HOV and AUVs are performing a special investigation mission. The main task is to search for underwater target objects in unfamiliar sea areas.  
The task of the AUV cluster is to perform high-precision topographical mapping and target recognition for the most probable area of the target, and to determine the coordinates of the suspected target. The double-sided effective strip width of the sounding side-scan sonar is 350 m, the parallel detection width of the three AUV clusters is approximately 2.1 km, and the detection navigation speed is 1 km. The main task of the HOV is to conduct accurate near-bottom inspection and investigation of the target. The operating range is approximately 40 \(\times\) 50 km, and the work area is shown in Figure 17.  
If the USV-based cooperative operational mode is used to complete the above tasks, the cluster of AUVs can work together in a certain direction, and the USV can move with the AUV cluster. At this time, the operational path can be planned as a straight line, and the detection area to complete one dive is approximately 155 km\({}^{2}\), which takes 50 h. The operational diagram is shown in Figure 18a, and 13 cooperative operational dives are required to complete the entire area. If the lander is used to complete the target detection in the target sea area, since the submersible mark system is stationary on the seabed and limited by the maximum communication distance, the AUV cluster cannot be detected along a straight line but can only be planned as a polyline.  
In this way, useless routes will inevitably appear, which will require underwater operational time. One operational dive can only complete the side sweep task of 144 km\({}^{2}\) in a square area of 12 km \(\times\) 12 km, which reduces the operational efficiency and takes 55 h. Figure 18b depicts the operation diagram. This mode also requires frequent placement and correction of submerged buoys, occupying research vessel R/V time. Using the operational mode based on the pure research vessel R/V is similar to using the lander mode except that each cooperative operational dive uses two AUVs to conduct detection tasks.  
Each operational dive can only complete a 96 km\({}^{2}\) detection area, which takes 52 h and requires 21 cooperative operational dives to complete the entire area. Table 1 lists the operational and dive times of the aforementioned three cooperative operational modes for the same operating task.  
The total operating times of the USV, lander, and pure research vessel R/V modes are 650, 770, and 1092 h, respectively. The total operating time of the USV mode is 120 h less than that of the lander mode, which is approximately 18.5% and 442 h less than that of the  
Figure 16: (**a**) Cooperative operating radius. (**b**) Operating time within different operating radii.  
pure research vessel R/V mode, which is approximately 68.0%. To some degree, the USV mode can be considered as the most efficient. Thus, in the search and salvage scene of a large-scale underwater target, if sea conditions allow it, we should adopt the underwater cooperative operation based on the USV mode.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Work Mode** & **Single Job Time (h)** & **Single Operating Area (km2)** & **Total Dives** & **Total Operating Time (h)** \\ \hline USV & 50 & 155 & 13 & 650 \\ Lander & 55 & 144 & 14 & 770 \\ Pure research & 52 & 96 & 21 & 1092 \\ vessel R/V & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Operational time and dive times of the three cooperative operational modes.  
Figure 17: Operating area map.