Detecting shifts of submarine sediment boundaries using side-scan mosaics and GIS analyses

Daphnie S Galvez,Svenja Papenmeier,H Christian Hass,Alexander Bartholomae,Vera Fofonova,Karen Helen Wiltshire

doi:10.1016/j.margeo.2020.106343

Abstract

Detecting changes of sediment boundaries on the seafloor is important for a better understanding of sediment dynamics and related impacts to benthic habitats. Side-scan sonars (SSS) perform more cost-effectively in shallow waters than other acoustic systems because of their larger swath widths, and the resolution of its images does not change with varying water depth. However, as they are generally towed behind the survey vessel, they tend to have lower positioning accuracy, which makes them unreliable for change detection analyses. In this study, we present a workflow that processes SSS data in a way that makes them fit for change detection analyses. To test the capacity of SSS mosaics for change detection, we used a free software called “Digital Shoreline Analysis System”, which was developed by the United States Geological Survey for ArcGIS version 10.4 onwards. The methods were applied in three areas in the Sylt Outer Reef, German Bight, North Sea. Our results showed that with appropriate processing, SSS mosaics could be used for change detection of sharp sediment boundaries. We found a common trend in the sediment distribution patterns of coarse sediments by monitoring the movement of their boundaries. The boundaries moved in northeast-southwest direction and boundary movements of less than 20 m were typically observed. The methods presented here are semi-automated, repeatable, and replicable, which has potential for wide-scale monitoring of sediment distribution patterns.

Highlights

Monitoring changes in sediment distribution pattern is important to understand the spatio-temporal patterns of environmental processes and the impact of human activities in the past decades (Auster et al, 1996; Rijnsdorp et al, 2020; Rumohr and Kujawski, 2000)
We considered the accuracy of the DGPS because we used the Multibeam Echosounder Systems (MBES) data to georeference the scan sonars (SSS) mosaics
Our results showed an improvement in the visual quality of the SSS mosaics in terms of backscatter contrast, reduction of artefacts, stitching of SSS strips, and layback correction

Summary

Introduction

Monitoring changes in sediment distribution pattern is important to understand the spatio-temporal patterns of environmental processes and the impact of human activities in the past decades (Auster et al, 1996; Rijnsdorp et al, 2020; Rumohr and Kujawski, 2000). Comprehensive monitoring of marine sedimentary ecosystems has been recommended to quantify large-scale and cumulative effects of anthropogenic impacts and to protect the sedimentary ecosystem (Heery et al, 2017) In this regard, detecting sediment shifts is important to locate and to monitor the impacts of sedimentological changes to benthic habitats, marine ecosystem services, and sediment dynamics on the seafloor (Eriksson et al, 2010; Montereale-Gavazzi et al, 2018; Thistle et al, 1985; Troell et al, 2005). SSS is sometimes preferred for sediment characterization because of its higher backscatter resolution than MBES backscatter data (Lucas et al, 2020; Michaelis et al, 2019b; Subarsyah and Arifin, 2019) It is ideal for large-scale seafloor monitoring because of its large swath widths and adjustable rope length of the tow-fish (Greene et al, 2018; Papastamatiou et al, 2020)

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Results

Conclusion