BATHYMETRIC SURVEY SYSTEM, BELUGA, WITH REAL-TIME PROCESSING CAPACITY-COMBINED USE OF GPS AND NARROW MULTIBEAM SOUNDER

摘要

Offshore civil engineering work in many cases requires accurate information about the seafloor topography or underwater structures. The conventional single beam sounder, however, cannot offset ship motions, in particular heaving, due to characteristics resulting from the wide directional angle of the beam. To solve such problems, the Beluga System was developed for bathymetric survey by combining the GPS and a narrow multibeam (NMB) sounder.rnThe new system can compensate for the motions of a survey ship with motion sensors and carry out the bathymetric survey with a NMB sounder. This enables accurate measurement of seafloor topography and is applicable to a survey line with a width two to seven times greater than water depth.rnThe main feature of the system is the realtime display function of graphic images on a personal computer with optionally decided mesh while measuring topographical data. This is achieved by presetting the latency obtained from patch tests (the latency is the difference between the time required for measurement and time required for data acquisition), the mount angle of the sonar head, and the sound velocity in seawater.rnThis feature permitted the system to be developed into a parallel-run system for measuring and dredging on a cutter suction dredger and a Seafloor Data Transmission System, an information collection system on deep seafloor, using a wireless LAN and cellular phones. Thus, the Beluga System is expected to be used in various ways.