Preliminary study on the distribution of artificial reefs by using multibeam echo sounder

In order to investigate the distribution of the artificial reefs (AR) in the coastal area for nautical charting and the stability study of the cast ARI multibeam echo sounder (MBES) was used. Side scan information can only be favorably used for the qualitative understanding of the distribution of AR. And deployment of the side scan towfish in the coastal area is a little bit difficult. The condition of settlement and scouring of AR is very hard to inspect by divers or ROV due to water turbidity. Therefore, it is a good idea to investigate the distribution, subsidence, horizontal movement, sand transport, and scouring of AR by using MBES. Bathymetry together with local current data around AR can be the basis of studying the mechanism of scouring and subsidence of AR. This study is trying to identify AR. High density and narrow beamwidth bathymetric data provided by MBES allows us to delimit the distribution of AR easily. However, it is not easy job to locate the individual AR and judge the orientation of AR. MBES data together with side scan image can support us to interpret to the orientation of the AR better. Heading measurements of the magnetic gyrocompass is less sensitive than that of true gyrocompass when vessel is turning. Therefore, one should be careful when heading data collected by magnetic gyrocompass and vessel is turning.