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Alfred Wegener Institute evaluates GeoTexture for Backscatter Data Processing in Arctic Nearshore Areas

2. December 2013

Back in 2012, the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) began assessing the pace of coastal erosion and the nature of sediment and organic matter transfer in nearshore areas of the southern Canadian Beaufort Sea. Coastal dynamics on arctic coasts are highly seasonal: ice is present from October to late June, thus the coast is armoured against wave erosion. In the short open-water season the coast is subject to the combined effects of mechanical and thermal processes resulting in high erosion rates along ice-rich permafrost coasts, such as the western Canadian Arctic. Current estimates show that there is about twice as much carbon stored in permafrost as in the atmosphere. Of special interest is the potential climate feedback triggered by carbon release into the nearshore zone by coastal erosion, in a region that according to many climate change models will experience disproportionate warming. A portion of the released carbon is deposited on the continental shelf, yet the nearshore dynamics and the possibility of sequestration in shallow waters remains an open question. Within the framework of the Coastal Permafrost Erosion research project (COPER), AWI scientists began investigating both the terrestrial coastal dynamics, as well as assessing the fate of sediments and carbon released into the nearshore.

An integral part of the fieldwork is seafloor mapping, for which AWI chose the Kongsberg GeoAcoustics GeoSwath Plus Compact multibeam echosounder. In the 2012 field season, c. 3.1 km2 of survey data were collected, along with surface sediment samples. Survey depths ranged from 1 - 17 m. The system delivers high-resolution bathymetry with coverage of up to 12 times the water depth in this shallow water environment and co-registered, geo-referenced backscatter data. Decisive factors in operating in remote and harsh environments are the portability and reliability of the equipment. The remote location makes it necessary to airlift all equipment and personnel. The surveys were carried out with an inflatable craft on which the splash protected (IP54) system was installed in a portable installation and powered by 24 V battery.

Regarding co-registered, geo-referenced backscatter data, AWI has recently evaluated GeoTexture, a Kongsberg GeoAcoustics software suite for backscatter data processing, mosaic creation and seabed classification. The performance of the software has been optimized for the analysis of GeoSwath Plus backscatter data, as it allows for beam pattern correction, vessel motion and sea-bottom topography, which substantially improve the quality of the mosaics and ease image analysis and interpretation.

Compensated backscatter mosaic from the near-shore south-east of the Herschel Island. The data was collected using a Kongsberg GeoSwath Plus Compact bathymetric sonar and processed using GeoTexture software suite. The survey vessel is an inflatable craft with the sonar head installed on a retractable pole together with peripheral sensors, motion reference unit, GPS and sound velocity probe. The splash protected deck unit is powered by batteries and operated via a ruggedised laptop.

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