# Deep-Sea Underwater Cooperative Operation of
## 3 Cooperative Operational Modes
### Lander-Based Mode  
In order to overcome the limitations of the USV and realize the AUV swarm to perform operational tasks in difficult sea conditions, we further propose a manned and unmanned cooperative operational mode based on the lander, as shown in Figure 8. It comprises of the research vessel R/V, lander, HOV, AUV cluster, and other equipment. The lander replaces the USV for monitoring the underwater AUV cluster operations. The lander can send the positioning information of the AUV cluster to the AUV cluster through the UACS. The research vessel R/V can perform HOV diving tasks in places with relatively long operating distances, to achieve a wider range of underwater operations.  
The lander is equipped with a USBL transponder, USBL, UACS, power system, motion sensor, and other modules, as shown in Figure 9. Limited by the size of the lander, the UACS and the USBL are highly integrated, which can realize the functions of communication and positioning simultaneously. To obtain the accurate position coordinates of the lander, after the lander is deployed, the research vessel R/V can use the USBL to accurately locate the transponders installed on the lander. Then, the coordinate information of the lander is sent to the communication positioning system installed on the lander through the UACS of the research vessel R/V.  
The lander calculates the relative position information of the AUV cluster and calculates the absolute geodetic coordinates of each AUV based on its own coordinates. It is sent to the AUV cluster through UACS to provide underwater orientation guidance for the AUVs. The AUV cluster performs operations on the seabed through a preset planning route. The AUVs use the autonomous decision-making system to complete underwater navigation, terrain mapping, and obstacle avoidance. After completing the task, they surfaced in turn and are recovered by the research vessel R/V.  
Figure 8: A scenario of cooperative operation based on a lander.  
Figure 9: Information flow of a cooperative operation based on a lander.  
This operational mode can also liberate the research vessel R/V so that the research vessel R/V can fully focus on the underwater operations of the HOV or perform routine investigation tasks in another area, which can considerably improve the scope of scientific investigations and the efficiency of offshore operations. Compared with the cooperative operational mode based on USVs, the lander can operate in severe sea conditions, and this poses less risk to the operation.  
Since the lander is relatively close to the AUV cluster and is unaffected by the swell current on the sea surface, the USBL on the lander is relatively geostatic and is superior to the USBL of the research vessel R/V in terms of positioning accuracy and positioning stability. Therefore, this operational mode has significant advantages in the fields of large-scale seab topographic mapping and mineral resource exploration.  
The disadvantage of this mode is that the cooperative operational command and monitoring system cannot monitor the position and ontology data of the AUVs in real time and cannot issue control instructions to the AUV. Relevant information can be obtained through the satellite communication system installed on the AUVs only when the AUVs are thrown to the surface. In addition, the lander cannot move with the AUV cluster as does the USV, which to a certain extent, limits the underwater operating range of the AUV cluster.