Investigators lower Jinghai 3, an unmanned boat, to conduct a geological survey off the coast of Sanya, Hainan province, on Oct 23, 2017. China sent two unmanned boats－Jinghai 3 and Jinghaihong－to survey the marine geological conditions in the Dongmaozhou Island off Sanya, where surveyors failed to carry out a field survey last year after ships ran aground. It was the first time that unmanned boats had been used in such a survey. [Photo/Xinhua]