# Deep-Sea Underwater Cooperative Operation of
## 5 Work Efficiency Analysis
### Unmanned Surface Vehicle/Lander Mode  
In the cooperative operational mode based on the USV/lander, the USV/lander system can monitor a cluster comprising three AUVs to conduct underwater operations simultaneously. In the actual operation, the first step is to deploy the USV/lander system. Since the position coordinates of the lander when sitting on the bottom are unknown, the position of the lander needs to be measured, and the research vessel R/V circles the lander to accurately calibrate the position of the submerged buoy. AUV clusters are then deployed in turn to conduct underwater operations. When the AUV deployment operation is completed, the research vessel R/V transports the HOV to the operational area to conduct underwater investigation operations. During the manned deep diving operation, the research vessel R/V monitors the operational dynamics in real time near the HOV.  
If the manned deep diving operational area is 100 nm away from the USV/lander, the ferry time of the research vessel R/V will take 5 h. After the manned deep diving operation is completed, the research vessel R/V will sail to the AUV operational area to recover the AUV clusters in turn and finally complete the recovery of the lander and USV. Figure 14 shows the USV/lander-based collaboration time. It takes approximately 50 h to use the USV and approximately 55 h to use the lander to complete the same task.  
In the traditional distributed operational mode relying on the research vessel R/V, one HOV and three AUVs complete their operations and are recovered, and then a submersible is deployed. The operational time is shown in Figure 15. It takes 165 h, including the transit time to the research vessel R/V to complete the same task at the same operating location. When performing large-scale and long-distance underwater surveys, the introduction of a USV/lander cooperative operation was determined to have considerable advantages in terms of the operational time. This operational mode uses the AUV cluster operational gap to perform underwater operations of the HOV, which saves the research vessel R/V time and expands the operational scope.  
It should be noted that the above operational scope is not infinitely expandable, and specific analysis needs to be performed depending on the operational radius and specific tasks. If the distance is too far, the transit time will be too long, and the research vessel R/V will not be able to recover the AUV cluster. If the operating range is relatively short or the USV follows the AUV cluster to move toward the research vessel R/V, the transit time could be reduced, and the AUV operational gap could be used to perform two HOV dive missions to further improve the operational efficiency. Figure 16a shows a schematic diagram of the cooperative operational scope based on the USV/lander. Figure 16b shows the statistics of operating time in different operating radii.  
Figure 13: Time sequence allocation of underwater positioning communication.  
Figure 14: Elapsed time in cooperative operational mode based on a lander/USV.  
Figure 15: Elapsed time in traditional distributed operational mode (one HOV and Three AUVs).