Integrated hydro-acoustic survey scheme for mapping of sea bottom ecology

Abstract

An integrated hydro-acoustic survey scheme for mapping sea bottom ecology is proposed. The proposed method enables the sea bottom geology and ecology to be mapped more economically. As the importance of sea bottom ecology mapping increases, the need for an efficient mapping method has increased. The use of multibeam sonar to map seagrass beds has been proposed. Using multibeam sonar, the 3D distribution of seagrass beds can be mapped. Since the swath width of multibeam sonar depends on water depth, the productivity of survey work declines in shallow areas. On the other hand, the productivity of survey work done by side scan sonar is relatively good in shallow areas, since the scan range of side scan sonar is independent of water depth. The quality of side scan sonar images has been improved, and such images now allow easy recognition of sea bottom materials, seagrass beds, etc. Therefore, it is possible to determine the horizontal distribution of seagrass beds by using side scan sonar. However, the 3D distribution of seagrass beds cannot be mapped by this method. In view of the features of both types of apparatus, we studied the integration of side scan sonar and multi-beam sonar, and conducted a case study. At the water depth of 5 m, the survey productivity of side scan sonar is approximately five times that of multibeam sonar. Since side scan sonar is more efficient in shallow areas than multibeam sonar, surveys by side scan sonar should be done before those by multibeam sonar. By using side scan sonar images, the area for the multibeam sonar survey can be determined. Swath bathymetric surveys can be carried out only for seagrass bed areas. The total time required for this integrated survey scheme might be less than that by multibeam sonar only. This survey scheme is economical and effective for mapping seagrass beds.