Development of Acoustic Colour Technique Using Multi-Frequency Swath Acoustic Backscatter

TitleDevelopment of Acoustic Colour Technique Using Multi-Frequency Swath Acoustic Backscatter
Publication TypeConference Proceedings
AuthorsDuffy, G, Rzhanov, Y, Rinde, E, Horvei, B, Brown, C
Conference NameUnderwater Acoustics
Conference DatesJune 22-27
Conference LocationRhodes, Greece
Keywordsacoustic classification, multi-frequency, multibeam

Swath acoustic data collected by multibeam sonar systems is a recognised tool to efficiently map the bathymetry and texture of large areas of seabed so aiding the definition of benthic habitats. Backscatter data may be spatially classified based on either standard measurements of characteristic acoustic angular response curves (ARCs) or backscatter model parameters (inverted from the ARCs) that depend on seabed physical properties. However, the inverted model parameter of “roughness” is intrinsically linked to the acoustic wavelength; only the roughness spectrum with wavelength less than half of the acoustic wavelength affects the surficial acoustic backscatter. Therefore, inferred surficial texture is intrinsically acoustic frequency-dependent. This research tests the feasibility of using multifrequency acoustic backscatter to create acoustic classes based on a broadband acoustic response to natural roughness spectra. The goal is to generate more accurate spatial delineation of facies. EM2040D (300 kHz (continuous wave (CW) pulse)), EM710 (100 kHz (CW)) and EM302 (30 kHz (CW)) benthic acoustic data were collected simultaneously using Kongsberg Maritime’s test vessel, Simrad Echo, within the Ormø–Færder Marine Protected Area in Oslofjorden, Norway. 47 line-km of multi-frequency data were collected resulting in a survey extending 2.9 km by 3.2 km. In addition to the latter overlapping survey lines, 5 non-overlapping, 2.9 km-long cross-lines were acquired to investigate anisotropic backscatter effects; the crosslines were run perpendicular to bathymetric contours to minimise variation of possible depthdependent benthic texture within a swath. This paper discusses the results of delineations and compares maps for datasets separately and jointly classified with different frequencies.

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