Seabed mapping using multibeam swath-mapping systems: an essential technology for mapping Australia's margins

Swath-mapping of the seabed started soon after the Second World War, with small towed sidescan sonars providing images and built-in multi beam sonars providing bathymetry contour maps.  Since then, variants of both systems have developed enormously to cover all water depths, and many of them can produce both acoustic imagery and contours. Today, swath widths of up to seven times the water depth allow rapid and accurate mapping. Swath-mapping has largely replaced the far less efficient single-beam profiling as a mapping tool.  Several deepwater systems have been used on the Australian margin, and this paper concentrates on their use. At this stage, less than 5% of Australias offshore jurisdiction (larger than our onshore jurisdiction) has been mapped. HMAS Cook was brought into service in the 1960s with a very early SeaBeam multibeam system. Its most notable scientific successes were in 1989, when it was used in conjunction with the long-range towed GLORIA sidescan sonar system. Geologically important results were obtained off the Great Barrier Reef, south of Sydney, and west of Robe in South Australia.  Since then, a number of transits through Australian waters, using modern SeaBeam systems, have been carried out by US institutions. In 1997, AGSO used R.V. Melville to map a large area off eastern Tasmania and in Bass Strait.  Spectacular sidescan sonar images (with far higher resolution than those from GLORIA) and associated bathymetry have been obtained in the back-arc basins of Papua New Guinea by the SeaMarc II and HMR1 systems. The first major HMR1 survey in Australian waters was carried out in 1994 on the Macquarie Ridge with AGSO providing R.V. Rig Seismic as the platform.  In 1994, AGSO used the French R.V. L Atalante with the Simrad EM12D multibeam system for mapping off Tasmania. The magnificent contour maps and images have revolutionised our geological understanding of an area three times that of Tasmania, and have enabled us to target seabed sampling programs for a greatly improved understanding of geological evolution and petroleum potential. These maps have been of substantial benefit to fishermen and biological and fisheries researchers, as have the Melville maps from eastern Tasmania. Several transit surveys using L Atalante have provided useful maps elsewhere off Australia.  Government is considering how to develop our knowledge base to allow effective management of our vast offshore jurisdictional area: a 200 nautical mile Exclusive Economic Zone; and, beyond that, an extension of the legal Continental Shelf, which AGSO has been directed to map by 2004, to allow a maximum claim under the UN Law of the Sea provisions. A key element in management activities is adequate maps, which require methodical mapping of the seabed, using swath-mapping techniques. The RAN Hydrographic Service is acquiring vessels and systems capable of mapping the continental shelf.  A national program, to map the entire Australian jurisdiction of 10 million km" beyond the continental shelf, but excluding the Australian Antarctic Territory, would take about 12 years and cost about $ 150 million, including all facets from acquisition to processing and storage, interpretation, and provision of digital data to the public. Such a program has strong multidisciplinary scientific, industrial and bureaucratic support, and would provide the information to properly manage our jurisdiction.

Tags: Earth Sciences, GA Publication, Journal, Published_External, marine
Organization: Australian Ocean Data Network