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26 st / May 2016 www.sea-technology.com coupled transmission system equipped with temperature and depth sensors can transmit real-time measurements with an error rate less than 10 -5 . In another test, in the Bohai Sea in September 2015, the system was set up with three sets of sensors on a chain to measure surface temperature, salinity and depth data once per hour for one month. This setup was also tested in low-temperature freshwater lakes (ice water) in northeast China in November 2015. By improving signal strength and adding a checksum algorithm to ensure transmission reliability, the system was able to transmit both at sea and in low- temperature freshwater. The low-temper- ature environment of -25° C could have caused irreversible damage to the circuit components and the ring, but this was avoided by using temperature-resistant ferrite material for the magnetic ring and core. The tests in the Bohai Sea and northeast China lakes yielded a transmis- sion error rate less than 10 -5 . Conclusion The inductively coupled data moni- toring and transmission system was de- signed to achieve real-time underwater monitoring with various sensors, suit- able for several platforms, such as buoys, boats and submarines. Testing has prov- en that the system works well in marine and freshwater environments, with transmission ef- fectiveness and reliability. In the future, the system will be developed with faster transmission rates and farther transmission distances. Acknowledgments This article is supported by the National Natural Science Foundation of China. ST protocol to achieve communication between the node communicator and various underwater measuring instru- ments that can be from different manufacturers. The system has a half-duplex communication mode, with a communication rate up to 9,600 bps and transmis- sion distance up to 2 km. It can operate for more than two years. Testing The data monitoring and transmission system has al- ready been applied in several settings with instruments on buoy platforms, leading to promising results. In one test, the system was installed with 18 temper- ature-depth sensors and has been operating in the Dan- jiangkou Reservoir since December 2013. The system is fxed in a pressurized watertight housing, with induction ring on the upper end. The induction ring was designed to be split into two parts to ensure easy installation on the cable. This lake test is proving that the inductively (Top) Images of testing conducted in lake water, seawater and ice water. (Bottom) Parameters of various water environments. Zhang Xiaowei is an engineer at China's National Ocean Technology Center, focusing on marine envi- ronmental data transportation technology. She par- ticipates in national and provincial scientifc projects. Deng Yun is a senior engineer at China's National Ocean Technology Center and is the deputy direc- tor of research. He focuses on marine environmental monitoring and investigation. Jiang Fei is an engineer at China's National Ocean Technology Center. He focuses on marine environ- mental data acquisition technology and participates in national and provincial scientifc projects.