## 3 Efficient Data Recovery Strategy Design  
We designed a low-power and high-efficiency data backhaul strategy to ensure that the success rate of data backhaul is not less than 90% when the system is in a complex and changeable marine environment for a long site operation. The SCB is affected by weather and the sea state. A bad sea state and strong surface currents will impact the stability of data acquisition and transmission, and the SCB will sink below the sea surface, which will greatly reduce the success rate of satellite communication. Increasing the number of satellite communications in that scenario has a small effect on the system but at the same time will cause a large increase in the system's power consumption, which cannot meet the long-term on-site work requirements. If the battery capacity increases, the volume of the SCB will follow, the concealment will decrease, and the overall cost will increase.  
In order to meet the long-term working requirements and ensure high-efficiency data return based on the hardware functions of this system, we designed a low-power-efficient decision data recovery strategy. The algorithm logic flow is shown in Figure 10. After the system performs the data collection operation, it will move to the satellite communication state. At this time, the water entry detection function is used to detect the current state of the SCB. If it is detected that the SCB is below the sea surface, the current packets will be marked as historical data and stored for subsequent re-send operations, which is followed immediately by the sleep state to wait for the next data collection to start. If the SCB is on the sea surface, the current signal quality will be detected by the satellite module. If the signal quality is low, it means that the system will try to return the current data packet and directly enter the sleep state. If the signal quality is good, the current data packet will be transmitted first. Then if there is a historical data packet, the re-send operations will be performed in order. During this period, the signal quality of the satellite module will be monitored. If the signal quality becomes poor, the system will stop data retransmission and enter the sleep state. In addition, the system can also enable the satellite to perform two-way communication at a set period every day. During this period, the SCB can receive commands from the receiver at the ground station and perform historical data reissue operations. The ground station operator can check the weather, current, and wave parameters of the sea area where the system is located and select a period with a good sea state to enable two-way satellite communication. At this time, the success rate of satellite communication will be greatly improved and the efficiency of historical data reissue will be guaranteed. Through the above-mentioned SCB status detection, satellite communication quality detection and historical data reissue strategy, the data return efficiency of this system will be significantly improved, the average power consumption will be effectively reduced, and the long-term on-site working ability will be greatly enhanced.  
Figure 9: Software block diagram of SCB.