Detection of Stones in Marine Habitats Combining Simultaneous Hydroacoustic Surveys

Svenja Papenmeier,H Hass

doi:10.3390/geosciences8080279

Svenja Papenmeier, H Hass

Open Access

https://doi.org/10.3390/geosciences8080279

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Abstract

Exposed stones in sandy sublittoral environments are hotspots for marine biodiversity, especially for benthic communities. The detection of single stones is principally possible using sidescan-sonar (SSS) backscatter data. The data resolution has to be high to visualize the acoustic shadows of the stones. Otherwise, stony substrates will not be differentiable from other high backscatter substrates (e.g., gravel). Acquiring adequate sonar data and identifying stones in backscatter images is time consuming because it usually requires visual-manual procedures. To develop a more efficient identification and demarcation procedure of stone fields, sidescan sonar and parametric echo sound data were recorded within the marine protected area of “Sylt Outer Reef” (German Bight, North Sea). The investigated area (~5.900 km2) is characterized by dispersed heterogeneous moraine and marine deposits. Data from parametric sediment echo sounder indicate hyperbolas at the sediment surface in stony areas, which can easily be exported. By combining simultaneous recorded low backscatter data and parametric single beam data, stony grounds were demarcated faster, less complex and reproducible from gravelly substrates indicating similar high backscatter in the SSS data.

Highlights

IntroductionHard substrates like cobbles, boulders, blocks and bedrock provide essential ecosystem functions [1,2]
In sublittoral environments, hard substrates like cobbles, boulders, blocks and bedrock provide essential ecosystem functions [1,2]
Backscatter coding: Acoustic ground discrimination systems (AGDS) data points are colored in the SSS backscatter gray value that occurred at the point location

Summary

Introduction

Hard substrates like cobbles, boulders, blocks and bedrock provide essential ecosystem functions [1,2]. Single stones (cobble, boulders and blocks) in areas where soft substrates dominate, are hotspots for marine biodiversity [3]. The localization, mapping and documentation of stones in the North Sea (and elsewhere) gains increasing importance since the European Union (EU) implemented the protection of stony areas in the European seas in 1992 [5]. In the German Bight, existing area wide sediment distribution maps [6,7] were interpolated from grab-sample data, which lack resolution and tend to under-represent “coarse sediment” (gravel and stones). Stones can hardly be representatively sampled with grab samplers

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