Impact of Sparse Benthic Life on Seafloor Roughness and High-Frequency Acoustic Scatter

Schönke, Mischa; Wiesenberg, Lars; Schulze, Inken; Wilken, Dennis; Darr, Alexander; Papenmeier, Svenja; Feldens, Peter

doi:10.3390/geosciences9100454

Cited by 5 publications

(4 citation statements)

References 34 publications

(75 reference statements)

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“…The influence of flora and fauna on backscatter characteristics of sediments is known from diverse studies [91][92][93][94][95]. While single beam systems are established for the discrimination of colonized and non-colonized hard substrates [36,96,97], the effect of benthic organisms on SSS and MBES backscatter characteristics of stones is still unknown.…”

Section: Hydroacoustic Mapping Techniquesmentioning

confidence: 99%

Hydroacoustic Mapping of Geogenic Hard Substrates: Challenges and Review of German Approaches

et al. 2020

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Subtidal hard substrate habitats are unique habitats in the marine environment. They provide crucial ecosystem services that are socially relevant, such as water clearance or as nursery space for fishes. With increasing marine usage and changing environmental conditions, pressure on reefs is increasing. All relevant directives and conventions around Europe include sublittoral hard substrate habitats in any manner. However, detailed specifications and specific advices about acquisition or delineation of these habitats are internationally rare although the demand for single object detection for e.g., ensuring safe navigation or to understand ecosystem functioning is increasing. To figure out the needs for area wide hard substrate mapping supported by automatic detection routines this paper reviews existing delineation rules and definitions relevant for hard substrate mapping. We focus on progress reached in German approval process resulting in first hydroacoustic mapping advices. In detail, we summarize present knowledge of hard substrate occurrence in the German North Sea and Baltic Sea, describes the development of hard substrate investigations and state of the art mapping techniques as well as automated analysis routines.

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Section: Hydroacoustic Mapping Techniquesmentioning

confidence: 99%

Hydroacoustic Mapping of Geogenic Hard Substrates: Challenges and Review of German Approaches

et al. 2020

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“…It can be assumed that features such as worm casts and worm tubes affect volume scatter, as has been demonstrated in the laboratory (Schulze et al, 2021). However, the effects are so far difficult to quantify for the seafloor with low benthic coverage (Schönke et al, 2019). Benthic macrofauna in the CSG facies is low in biomass, abundance, and species richness, but significant amounts of blue mussels (M. edulis) are found in April and August.…”

Section: Coarse Sand and Gravelmentioning

confidence: 95%

Seasonal change of multifrequency backscatter in three Baltic Sea habitats

Schulze

Gogina

Schönke

et al. 2022

Front. Remote Sens.

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This study investigated the seasonality of acoustic backscatter intensities, exploring three habitats in the southwestern Baltic Sea: 1) a mussel-covered reef, 2) coarse sand and gravel, and 3) seagrass meadows. Backscatter information of different, partly calibrated frequencies (200, 400, 550, and 700 kHz) was collected in three seasons (May, August, and October). The acoustic data were supported by point samples and video profiles for grain size and benthic community analysis. Angular response curves helped to quantify the seasonal backscatter response of the different frequencies. The multifrequency and multiseasonal backscatter maps distinguish the three habitats and reveal variable seasonal differences in acoustic backscatter, but not all changes in the benthic community can be recognized in the acoustic data. 1) The high-backscatter response of the mussel-covered reef shows little seasonal differences and was frequency independent. 2) The ecologically valuable coarse sand and gravel areas show small-scale seasonal alterations in the sediment composition and morphology, mainly caused by changes in local hydrodynamics. Higher frequencies were found best suited to identify coarse sand and gravel. 3) Seagrass meadows seasonality is dominated by growth of seagrass blades, increasing the backscatter response compared to bare sand. The use of multiple frequencies is beneficial as the low frequency is sensitive to changes in the shallow subsurface and benthic features such as seagrass rhizomes, while the higher frequency highlights changes related to coarser sediment.

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“…Ad- ditionally, difference between 90 and 300 kHz was relatively small, considering that our study area only included fine to coarse sand. As an important benthic species in the North Sea, L. conchilega builds tubes with sand and shell fragments, which can protrude out of the sediment for several centimeters, thereby increasing the local seabed roughness [29][30][31].…”

Section: Comparison Between Acoustic Classes and Top-layer Ground Truthmentioning

confidence: 99%

Characterizing seabed sediments using multi-spectral backscatter data in the North Sea

Bai,

Mestdagh,

Snellen

et al. 2023

OCEANS 2023 - Limerick

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Acoustic classification using single-beam and multibeam echosounders has been widely applied in characterizing seabed sediments. Although previous studies have shown a better discrimination of fine and coarse sediments using multispectral echosounder data, analysis regarding comprehensive seabed sediment properties is still needed. In this study, we used single-beam data of 24 kHz, as well as multi-beam data of 90 and 300 kHz to investigate the benefits of multi-spectral backscatter data in describing sediment properties including median grain size; weight percentages of gravel, sand, and mud; volume percentages of stones, shell fragments, and living bivalves; as well as density of acoustically hard animals (molluscs and the tube-building worm Lanice conchilega). We classified data of each frequency in an unsupervised manner, using K-means clustering for the single-beam echo time series and Bayesian classification for the multi-beam backscatter. Compared with the top-layer sediment properties, we found classification of 90 and 300 kHz consistent with variations of median grain size and L. conchilega density, whereas classification of 24 kHz can also be related to the percentages of shell fragments and stones. In addition, one acoustic class of 24 kHz might indicate a higher gravel content in the subsurface of the study area. Although quantitative relationships between backscatter and sediment properties are still difficult to achieve given a limited number of samples, using multi-spectral backscatter data is a potential approach to characterize seabed sediments from various perspectives.

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Impact of Sparse Benthic Life on Seafloor Roughness and High-Frequency Acoustic Scatter

Cited by 5 publications

References 34 publications

Hydroacoustic Mapping of Geogenic Hard Substrates: Challenges and Review of German Approaches

Hydroacoustic Mapping of Geogenic Hard Substrates: Challenges and Review of German Approaches

Seasonal change of multifrequency backscatter in three Baltic Sea habitats

Characterizing seabed sediments using multi-spectral backscatter data in the North Sea

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