Acquisition and processing of backscatter data for habitat mapping - comparison of multibeam and sidescan systems

Often marine habitat surveys use multibeam bathymetry systems to model the seafloor. This describes the morphology but not the terrain lithology or substrate. Backscatter imagery helps the interpreter to better classify the physical environment that may support a particular biological community. In this contribution, the acquisition performance of both multibeam and sidescan sonar backscatter imagery are contrasted and examples shown. The logistical factors affecting the two systems during surveying are discussed and data from both systems compared. Choice of systems for habitat mapping is discussed. A relative cost analysis of the various survey systems is presented with varying resolution and coverage. The size and shape of the footprint, and thus resolution, is variable dependant on many factors, including ship speed, data processing and sampling. The resolution and formation of imagery is important, but high sampling rates are shown not to be a complete solution as over-sampling can present a false impression of high resolution. However, it is suggested that backscatter imagery should have least 7 bit sensitivity to aid visual and digital inspection. Habitat mapping examples are shown using multibeam backscatter and sidescan sonar, where the processing has been optimised for backscatter imagery. A key question is how much of high resolution bathymetry data is essential for habitat mapping, and whether backscatter imagery can provide more of the information required at a higher resolution than a bathymetric morphology map.

[1]  Abraham Lempel,et al.  Compression of individual sequences via variable-rate coding , 1978, IEEE Trans. Inf. Theory.

[2]  Philippe Blondel,et al.  Textural analyses of sidescan sonar imagery from two mound provinces in the Porcupine Seabight , 2002 .

[3]  M. L. Somers,et al.  Quantitative backscatter measurements with a long-range side-scan sonar , 1989 .

[4]  John E. Hughes Clarke,et al.  Classification of seafloor geology using multibeam sonar data from the Scotian Shelf , 1994 .

[5]  Ronald L. Huston,et al.  Modeling of Variable Length Towed and Tethered Cable Systems , 1999 .

[6]  Xavier Lurton,et al.  An Introduction to Underwater Acoustics: Principles and Applications , 2010 .

[7]  B. Bett,et al.  The origin of deep-water, coral-topped mounds in the northern Rockall Trough, northeast Atlantic , 2003 .

[8]  Luciano E. Fonseca,et al.  SEAFLOOR CHARACTERIZATION THROUGH THE APPLICATION OF AVO ANALYSIS TO MULTIBEAM SONAR DATA , 2005 .

[9]  L. Mayer,et al.  Shallow-water imaging multibeam sonars: A new tool for investigating seafloor processes in the coastal zone and on the continental shelf , 1996 .

[10]  M. L. Somers,et al.  GLORIA image processing: The state of the art , 1990 .

[11]  K. Vickery,et al.  Acoustic positioning systems. A practical overview of current systems , 1998, Proceedings of the 1998 Workshop on Autonomous Underwater Vehicles (Cat. No.98CH36290).

[12]  Philippe Blondel,et al.  Handbook of seafloor sonar imagery , 1997 .

[13]  D. Pugh.  Tides, Surges and Mean Sea-Level , 1987 .