The purpose of this paper is to describe the new methods of engineering investigation for pre-stage cross-sea passage project and new methods of monitoring after project completion. Based on the analysis of hi-tech equipment and new technologies used at present in seafloor exploration and monitoring, their application feasibility in construction of cross-sea passage is studied. It is shown that applications of synthetic aperture sonar system, three-dimensional imaging system, sub-bottom profiler detection system and other new hitech equipment can obtain data more comprehensively, accurately and efficiently than current common equipment and provide more comprehensive and accurate methods for cross-sea passage construction investigation and the passage's safe operation. Making full use of these modern hi-tech methods may conduct overall and correct investigation and monitoring to detect risk and implement assessment, as well as work out preventive and control measures in time, so as to guarantee the safe construction and operation of passages.

cross-sea access project  /  project investigation and monitoring  /  double-frequency synthetic aperture sonar  /  three-dimensional imaging sonar