Abstract: To address the limitations of embedded processing resources, the restricted payload capacity of BeiDou short messages, and the degradation of data transmission continuity caused by fluctuations in maritime communication conditions during long-term observations with multi-layer conductivity-temperature-depth (CTD) ocean buoys, a multi-layer CTD data acquisition and reliable transmission method based on BeiDou short-message communication is proposed. The system employs real-time clock (RTC)-based periodic scheduling and time-shared module powering to accomplish multi-layer sensor acquisition, positioning and time synchronization, and data packetization. Continuous sampling, first-sample rejection, validity checking, and averaging are adopted for data preprocessing. A 16-bit fixed-length integer encoding scheme combined with fixed-field encapsulation is used to reduce transmission redundancy. In addition, signal-strength assessment, transmission-status confirmation, and Flash-based data caching and retransmission are integrated to improve data-return reliability under weak communication conditions. Sea-trial results show that the system can continuously acquire multi-layer CTD observations, achieving an overall data reception rate of 98.74%. In a dedicated cache-retransmission test involving two prolonged reception interruptions, all 465 observation records generated during the test period were eventually received after link restoration, demonstrating the effectiveness of the Flash-based cache retransmission mechanism under intermittent communication outages. Power-consumption tests further show that the on-demand module powering strategy reduces the current during inactive periods by more than 90%. These results demonstrate the engineering applicability of the proposed method for continuous multi-layer CTD buoy observations, communication-outage tolerance, reliable data recovery, and low-power operation.

Key words: ocean buoy, multi-layer temperature-salinity-depth observation, BeiDou short-message communication, fixed-point encoding, cache retransmission, reliable transmission