by CERF Hub scientist Dr R J Kloser

A recent review of acoustic remote sensing methods to map the seabed for marine-habitat mapping initiatives provides the context of current practice and future directions (Anderson et al., 2007). 

Abstract: 

Acoustic remote sensing of the seabed using single-beam echosounders, multibeam echosounders, and sidescan sonars combined and individually are providing technological solutions to marine-habitat mapping initiatives. We believe the science of acoustic seabed classification (ASC) is at its nascence. A comprehensive review of ASC science was undertaken by an international group of scientists under the auspices of ICES. The review was prompted by the growing need to classify and map marine ecosystems across a range of spatial scales in support of ecosystem-based science for ocean management. A review of the theory of sound-scattering from seabeds emphasises the variety of theoretical models currently in use and the ongoing evolution of our understanding. Acoustic-signal conditioning and data quality assurance before classification using objective, repeatable procedures are important technical considerations where standardisation of methods is only just beginning. The issue of temporal and spatial scales is reviewed, with emphasis on matching observational scales to those of the natural world. It is emphasised throughout that the seabed is not static but changes over multiple time-scales as a consequence of natural physical and biological processes. A summary of existing commercial ASC systems provides an introduction to existing capabilities. Verification (ground-truthing) methods are reviewed, emphasising the difficulties of matching observational scales with acoustic-backscatter data. Survey designs for ASC explore methods that extend beyond traditional oceanographic and fisheries survey techniques. Finally, future directions for acoustic seabed classification science were identified in the key areas requiring immediate attention by the international scientific community.

In the Australian context, there has been a steady uptake of acoustic technologies for mapping both shallow (<100 m) and deep water (>100 m) seabeds. The challenge remains to ensure that the bathymetric and seabed reflectivity data is collected, processed and archived appropriately so that scientists and managers can translate this large amount of data into information for prediction of biodiversity values and the sustainable management of our marine territory. On a national scale, the purchase of a mid-depth multibeam system for the national marine research vessel R.V. Southern Surveyor in 2004 has been a major boost to mapping offshore seabeds. A focus of the instrument’s deployment has been the outer shelf and upper slope seabeds, a region of high human use and due to its narrow width vulnerable to over-exploitation. In the SE region 67% of the seabed 200 m to 700 m has been mapped at 20 m resolution. To maximise mapping effort, transit time on the national facility is being used to fill gaps and map high priority areas. This mapping is finding new seabed assets/features (e.g. canyons, ridges, banks) that are important for biodiversity assessments and provides a necessary inventory for marine planning. The mapping also reveals that previously identified assets such as canyons and seamounts do not exist or are in a different location - vital information required when placing marine protected areas. Since 2004 only 3% of the marine territory has been mapped and only 11.8% in our target range of 200 to 700 m. With the reduction in funding to the marine national facility over recent years the rate of mapping on both research and transit voyages has slowed. There is a clear need to continue to map and understanding the shape and nature of the seabed to assist in managing our marine territory for now and into the future. This will need appropriate funding of our marine national facility and the groups that turn this acoustic data into information.

Reference: 

Anderson, J. T., Holliday, D. V., Kloser, R., Reid, D. G., and Simard, Y. (Eds). 2007. Acoustic seabed classification of marine physical and biological landscapes. ICES Cooperative Research Report, ICES, Copenhagen, Denmark.