Guideline for Seafloor Mapping in German Marine Waters

Using High-Resolution Sonars Guideline for Seafloor Mapping in German Marine Waters Using High-Resolution Sonars

Version 1.0 30.04.2016

This guideline has been developed by the following people:

Dr. Claudia Propp2 (Coordination) Dr. Svenja Papenmeier1 Dr. Alexander Bartholomä5 Dr. Peter Richter 3 Dr. Christian Hass1 Dr. Klaus Schwarzer 3 Dr. Peter Holler 5 Dr. Franz Tauber 4 Maria Lambers-Huesmann 2 Dr. Manfred Zeiler 2

1 Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Wadden Sea Station Sylt (AWI) 2 Federal Maritime and Hydrographic Agency (BSH) 3 Christian Albrecht University of Kiel, Institute of Geosciences (CAU) 4 Leibniz Institute for Baltic Sea Research, Department of Marine Geology (IOW) 5 Senckenberg am Meer, Wilhelmshaven © Federal Maritime and Hydrographic Agency (BSH) Hamburg and Rostock 2016 www.bsh.de

BSH No. 7201

This document should be cited as follows: BSH, 2016: Guideline for Seafloor Mapping in German Marine Waters Using High-Resolution Sonars. BSH No. 7201, 147 p.

Translated by ConTec Fachübersetzungen GmbH and reviewed by Dr. Claudia Propp

Cover photos by courtesy of: Dr. Svenja Papenmeier – AWI Dr. Franz Tauber – IOW Notice 3

Notice

This guideline was created under consideration of contributions from the following people:

Roland Atzler 10 Dr. Jürgen Knaack 8 Dr. Jan Witt 8 Cordula Berkenbrink 9 Kerstin Kolbe 8 Frank Wolf 5 Tim Bildstein11 Francesco Mascioli 9 Dr.-Ing. Andreas Wurpts 9 Dieter Boedecker 2 Wiebke Mildes 8 Christine Borgmöller 1 Dr. Roland Pesch 11 Michael Grotjahn 8 Dr. Christian Reimers 6 Dr. Wilfried Heiber 8 Dr. Klaus Ricklefs 3 Kathrin Heinicke 2 Dr. Alexander Schröder 8 Dr. Rolf Karez 6 Dr. Daniel Unverricht 4

1 German Federal Institute of Hydrology 2 German Federal Agency for Nature Conservation, Isle of Vilm branch office 3 Christian Albrecht University of Kiel, Research and Technology Centre West Coast 4 Geo Ingenieurservice Nord-Ost GmbH & Co. KG 5 Institute of Applied Ecology (IfAÖ) GmbH 6 Ministry for Agriculture, the Environment and Rural Areas of the State of Schleswig-Holstein 7 Schleswig-Holstein Agency for Coastal Defence, National Park and Marine Conservation 8 Lower Saxony State Office for Water Economy, Coastal and Environmental Protection, Brake-Oldenburg 9 Lower Saxony State Office for Water Economy, Coastal and Environmental Protection, Norderney Re- search Centre 10 Nautik Nord GmbH 11 BioConsult Schuchardt & Scholle GbR 4 Table of Contents

Part A – Instructions

Notice...... 3

List of figures...... 6

List of tables...... 6

Part A – Instructions...... 7

1 Introduction...... 7

2 Purpose...... 9

3 Updates...... 9

4 Data acquisition...... 10 4.1 The various mapping modes ...... 10 4.2 Survey methods and equipment ...... 12 4.3 Documentation of the work at sea ...... 17

5 Processing of backscatter data...... 18

6 Data interpretation...... 19 6.1 Preliminary remarks and definitions ...... 19 6.2 Data basis for the interpretation ...... 19 6.3 Basic specifications ...... 20 6.4 Sediment types ...... 20 6.5 Special cases ...... 23 6.6 Types of stone and boulder fields ...... 24 6.7 Seabed features ...... 24 6.8 Bedrock ...... 24 6.9 Other ...... 25

7 Work flow...... 25

8 Products...... 26

9 Bibliography...... 27

10 Standards and guidelines...... 29

11 Abbreviations and acronyms...... 30 Table of Contents 5

Appendix 1...... 31

Appendix 2...... 32

Appendix 3...... 33

Appendix 4...... 34

Appendix 5...... 35

Appendix 6...... 36

Part B – Hydroacoustic Catalogue for the German Marine Waters

1 Table of Contents...... 37

2 Sediment types...... 40

3 Bedrock...... 80

4 Seabed features – Dynamic sediment structures...... 82

5 Biogenic structures...... 96

6 Anthropogenic structures...... 106

7 Artefacts in the water column...... 128

8 Interference due to equipment and recording techniques...... 136 6 List of figures, List of tables

List of figures

Figure 1: Distribution of the areas for surface sediment mapping with 100 % spatial coverage in the German North Sea ...... 10 Figure 2: Distribution of the areas for surface sediment mapping with 100 % spatial coverage in the German Baltic Sea ...... 11 Figure 3: Diagram of the 100 % spatial coverage with side scan sonar. The outer edges of the swaths overlap by 10 %...... 11 Figure 4: Diagram of a minimum of 50 % spatial coverage with side-scan sonar ...... 12 Figure 5: Diagram for determining an appropriate combination of range and vessel speed for a resolution of 0.25 m in the along-track direction...... 14 Figure 6: Diagram for determining an appropriate combination of range and vessel speed for a resolution of 1 m in the along-track direction...... 14 Figure 7: Left: Clastic sediment types according to the simplified ternary system of Folk (1954) for the German marine waters. Right: The sand types I to IV according to the ternary system from Figge (1981), used only in the German North Sea...... 22 Figure 8: Exemplary illustration for special cases and spatial delineation of sediment types ...... 24 Figure 9: Flow chart for the mapping of sediment types ...... 25

List of tables

Table 1: Examples of the max. allowable vessel speed depending on the selected range to ensure the required resolution of 0.25 m in the along-track direction...... 13 Table 2: Examples of the max. allowable vessel speed depending on the selected range to ensure the required resolution of 1 m in the along-track direction ...... 14 Table 3: The four levels of classification in the high-resolution sediment type map of the German North Sea and Baltic Sea ...... 21 Table 4: Special cases...... ………………………...... 23 Table 5: The individual types of information provided in the digital map ...... 26 Instructions, Introduction 7

Part A – Instructions

1 Introduction

Various areas of application have a great need for spatial high-resolution information on the shape and nature of the seafloor. This includes the spatial distribution of seabed features resulting from geological and morpho- dynamic processes as well as the spatial distribution of sediment types and bedrock.

The areas of application include a wide variety of topics in connection with the ecosystem-based management approach (Baker and Harris, 2012) and with the interface of geology and geotechnical engineering (Poulos, 1988; Gerwick, 2007):

• Mapping of biotopes or types of biotopes The distribution of benthic habitats primarily depends on abiotic parameters such as the water depth, seafloor relief and sediment properties as well as the hydrographic regime such as the flow conditions near the seabed, salinity, temperature, suspended matter content and oxygen content.

• Marine environmental monitoring The seafloor is an essential compartment when analysing the marine material fluxes. It can work as a sink, a transfer area or a source depending on the prevailing physical, chemical and biological conditions. Sound knowledge of the distribution of the various types of sediment is relevant for the quantification of the in- tercompartmental fluxes of nutrients and pollutants between seafloor and the water column in the marine ecosystem.

• Fishery management Sediments are important indicators for fish spawning and feeding grounds. For these reasons there are already pictured in the “Fishery map of the North Sea at a scale of 1 : 900 000” (DHI, 1915 to 1976), which can be considered the first “habitat map” of its kind for the North Sea. Harris and Baker (2012) see the benefit of sediment maps in their high spatial resolution as an essential contribution to improved fishery management.

• Marine engineering In addition to its importance for the foundations of structures, the conditions of the seafloor are also important when laying submarine cables and pipelines. From the perspective of a geological engineer, knowledge of the distribution of underwater obstacles such as fields of stones or boulders or areas of till, for example, plays a very important role when planning cable and pipeline routes.

• Interest of the field of coastal engineering in the structure and dynamics of the seafloor Studying the sediments of shelf and marginal seas provides new insights into the past and current interac- tions between the sea and the coast, from which it is possible to forecast future developments. The results can be used as a foundation for answering questions arising in applications such as: how to adapt sediment management strategies for coastal protection measures; extraction of sand and gravel; more effective maintenance of shipping routes.

8 Instructions, Introduction

The BSH provides maps of the shape and conditions of the seafloor in the German sea areas in paper format or as digital datasets via the “GeoSeaPortal” on the BSH website. The topographic maps of the BSH are almost completely based on data obtained using single-beam echo sounders. Maps of the sediment distribution are based on grain size data from samples taken using a grab sampler at distances ranging from several hundred meters to one nautical mile or more (e. g. Laurer et al., 2013; Tauber, 2012).

To obtain information with a very high spatial resolution for the areas of application stated above, a new, comprehensive mapping program was initiated in cooperation with the German Federal Agency for Nature Conservation (BfN). The seafloor mapping of the German marine water is performed by primarily using side- scan sonar as a proven method (e. g. Storlazzi et al., 2013; Lurton, 2010; MESH Project, 2008; Coggan et al., 2007; Blondel, 2009; Kenny et al., 2003; Blondel & Murton, 1997; Johnson & Helferty, 1990) (section 4.2.1).

One of the primary motivation for the creation of innovative digital maps is the urgent need for detailed information on the sediment types, bedrock and seabed features for the national implementation of the European Habitats Directive and to create a regulatory framework for the measures in the area of water policy (WFD, MSFD).

This mapping guideline was produced in the framework of a cooperation agreement with the BfN, who made financial means available for the R&D cooperation agreements of the BSH with AWI, CAU and SaM. The IOW is involved via an administrative arrangement with the BSH.

This guideline presents the most recent status of the results compiled by the competent authority and was compiled together by the working group comprised of members from various scientific disciplines. From the authority’s point of view the compiled mapping techniques provide the instruments that appear to be appropriate and practical for extensively mapping the surface of the seafloor with high spatial resolution. Therefore, this compilation cannot take all requirements of scientific research into account. Instructions, Purpose, Updates 9

2 Purpose

This guideline describes a practice-oriented procedure for the operational implementation of the high spatial resolution mapping of submarine sediment types and seabed features in the German marine waters. The procedure is primarily based on the use of hydroacoustic devices (in particular side-scan sonar) and is adapted to the local and regional conditions in the North Sea and Baltic Sea. The standardized procedure intended to ensure consistent interpretations and results.

The products based on this edition of the mapping guideline comprise a dataset consisting of the following information: • Backscatter mosaic (see chapter 5); • Distribution of the sediment types within the different levels of classification (see section 6.4); • Quality of the spatial delineation, i. e. distinct and uncertain boundaries (see Fig. 7); • Solitary natural or anthropogenic structures.

This guideline integrates experience gained from work done by the BSH and from the following R&D projects: • WIMO scientific monitoring concepts for the German Bight, subproject 1.1 Habitat mapping of the seafloor; • Study of the sandbank and reef habitat types (Habitats Directive) habitat types in the EEZ of the German North Sea and Baltic Sea (Schwarzer & Diesing, 2006); • Identification of marine habitat types in the Mecklenburg Bay (Schwarzer et al., 2014a); • Identification of marine habitat types in the Bay of Kiel west of Fehmarn (Schwarzer et al., 2014b); • Acoustic seafloor classification in the North Sea – Sediment dynamics in the offshore environment, AMIN I (Papenmeier & Hass, 2014); • Acoustic seafloor classificationin the southern North Sea – Variability in the acoustic mapping of large- scale sediment type patterns in the German EEZ, ASKAWZ (Holler & Bartholomä, 2014); • Development of a standardized method for the full coverage mapping and description of sedimentological properties and processes on the surface of the seafloor in the Exclusive Economic Zone (EEZ) of the North Sea and Baltic Sea, SEDINO (Richter & Schwarzer, 2014); • Development of integrated model systems for analysing the long-term morphodynamics in the German Bight – AufMod (Heyer & Schrottke, 2013).

Furthermore, recommendations from EU projects (MESH, BALANCE) and the responsible working group of the ICES (WGMHM) were taken into account as well as the experience gained from project-related mapping-work done by CEFAS and the cross-institutional mapping program MAREANO in Norway. The relevant technical guidelines are listed in Chapter 10.

3 Updates

This mapping guideline presents the current state of the art in science and technology. It should therefore be considered a dynamic document. New experience and knowledge expected to be gained from further application of the guideline will be taken into account accordingly and incorporated into the mapping guideline during the update process. 10 Instructions, Data acquisition

4 Data acquisition

4.1 The various mapping modes

Due to different topographical and geological conditions of the various German marine waters, it appears expedient to use different mapping modes for the high-resolution mapping of sediment types.

The maps and information already available allow a segmentation of areas with a homogeneous sediment distribution and areas with a heterogeneous sediment distribution, which is based on the following fun- damentals and criteria.

Data basis: • The grid of the European Environmental Agency with an edge length of 10 km is used as the reference area. • In the German North Sea, the sediment distribution according to Figge (1981) from the joint project “Geo- potential of the German North Sea (GPDN)” of the BSH, LBEG and BGR (Laurer et al., 2013) was used. • In the German Baltic Sea, the mapping work “Seafloor sediments in the German Baltic Sea” (Tauber, 2012) was used. • On this basis, the deposits of medium to coarse sand and gravel (coarse material) were determined for each cell of the EU grid.

Criteria: • If coarse material is to be expected in a grid cell (see above), then the sediment distribution for this cell is classified as heterogeneous. • If only fine sand, silt and clay appear in a grid cell, then the cell is classified as a homogeneous sediment distribution.

By differentiating between areas with a homogeneous and a heterogeneous sediment distribution in this manner, the distribution of these areas in the North Sea and Baltic Sea help to decide whether to map the complete surface of the seafloor (see section 4.1.1) or whether to map only parts of it using a stripe-like mapping mode (see section 4.1.2).

Fig. 1: Distribution of the areas for surface sediment mapping with 100 % spatial coverage in the German North Sea. Instructions, Data acquisition 11

Fig. 2: Distribution of the areas for surface sediment mapping with 100 % spatial coverage in the German Baltic Sea.

4.1.1 “100 % spatial coverage” mapping mode

This mapping mode is to be used for collecting data in areas with a heterogeneous sediment distribution.

The line spacing of the hydroacoustic profiles should guarantee a full spatial coverage of the seafloor by the acoustic signals while simultaneously guaranteeing high data quality. Thereby, a 10 % overlap of the individual scanning swaths of two adjacent side-scan sonar profiles must be kept (Figure 3). Whenever external influences such as current and wind conditions, evasive manoeuvres or something similar cause gaps in the data aqusition, then these influences must be adequately documented. If necessary, these gaps will be closed later.

The preferred surveying method is the side-scan sonar in a towed mode (see section 4.2.1). To interpret the sonar data, it is necessary to sample and visually record the surface of the seafloor. This is referred to as “ground truthing” and is performed using grab samplers and UW video cameras (see sections 4.2.2 and 4.2.3).

Fig. 3: Diagram of 100 % spatial coverage with side-scan sonar. The outer edges of the swaths overlap by 10 %. 12 Instructions, Data acquisition

4.1.2 “At least 50 % spatial coverage” mapping mode

This mapping mode is normally used for data aquisition in areas with a homogeneous sediment distribution.

Depending on the swath width of the side-scan sonar, the spacing of the hydroacoustic profiles is twice the spacing of that selected for the “100 % spatial coverage” mapping mode (Fig.4), so that a spatial coverage of at least 50 % is achieved.

The preferred surveying method is the side-scan sonar in a towed mode. To interpret the sonar data, the sampling of the surface of the seafloor using grab samplers and UW video cameras is mandatory sections 4.2.2 and 4.2.3.

Fig. 4: Diagram of a minimum of 50 % spatial coverage with side-scan sonar.

4.2 Survey methods and equipment 4.2.1 Side-scan sonar

If possible, dual frequency systems should be used since in some cases sediment types and seabed features can be identified better using information from two different frequency ranges. Higher frequencies allow a higher level of detail when detecting objects, while lower frequencies enable the detection of areas at greater distance perpendicular to the direction of motion.

A frequency range of 200 to 600 kHz is recommended.

When specifying the vessel speed and the equipment settings, it must be ensured that the data recorded allows for the processing of a backscatter mosaic with a resolution of 0.25 m and 1 m in the across-track direction as well as in the along-track direction. The resolution in the along-track direction depends on the range and ship speed over the ground. For multi-pulse sonar devices, the resolution also depends on the number of pulses travelling through the water at the same time. Instructions, Data acquisition 13

This relationship can be described using the following formula, whereby the vessel speed always refers to the vessel speed over ground:

Max. vessel speed = Speed of sound in water × Resolution × Number of pulses 2 × Range

For a speed of sound in water of 1500 m/s and a resolution of 0.25 m, it is possible to calculate the maximum allowable vessel speed over ground in the following way:

Max. vessel speed or 𝑚𝑚𝑚𝑚 M𝑎𝑎𝑎𝑎푎 vessel speed ( )=187187.5. 5 × × Number Number of of pulses pulses M𝑎𝑎𝑎𝑎푎 vessel speed ( 𝑠𝑠)= Max. vessel speed𝑠𝑠 RRangeange ( m(m) ) 365365 × × Number Number of of pulses pulses MM𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎�𝑎𝑎𝑎𝑎𝑎𝑎𝑎� ( 𝑘𝑘𝑘𝑘(𝑘𝑘𝑘𝑘) )= = . . Range (m) For a resolution of 1 m, the following formulas apply: Range (m)

Max. vessel speed or 𝑚𝑚𝑚𝑚 M𝑎𝑎𝑎𝑎푎 vessel speed ( )=750750 × × Number Number of of pulses pulses M𝑎𝑎𝑎𝑎푎 vessel speed ( 𝑠𝑠)= Max. vessel speed𝑠𝑠 RRangeange ( m(m) ) 14581458 × × Number Number of of pulses pulses For single pulse sonar devices, the numberMM𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎�𝑎𝑎𝑎𝑎𝑎𝑎𝑎� of pulses must ( 𝑘𝑘𝑘𝑘( be𝑘𝑘𝑘𝑘) )=set = to 1. Incidentally, . dual. frequency does not Range (m) mean two pulses. Range (m)

It is explicitly pointed out that, due to the horizontal opening angle at which the sound waves are emitted, Bei Einzelpuls-Sonaren ist Pulszahl = 1 zu setzen. Dual-Frequenz bedeutet im Übrigen nicht Bei Einzelpuls-Sonarenthe specified resolution ist Pulszahl can only =be 1 obtainedzu setzen. at short Dual-Frequenz distances (up bedeutet to about im50 Übrigenm from the nicht sound source). zweizwei Pulse. Pulse. EsEs wird wirdTable ausdrücklich ausdrücklich 1 contains recommendations darauf darauf hingewiesen, hingewiesen, (black dass dassnumbers wegen wegen in bold)des des horizontalenspecifying horizontalen the Öffnungswinkels, max.Öffnungswinkels, allowable vessel in in speed de- demdem diepending die Schallwellen Schallwellen on the selected abgestrahlt abgestrahlt range. Thewerden, werden, values die showndie geforderte geforderte in italics Auflösungindicate Auflösung speeds nur nur imthat im Nahbereich are Nahbereich either too (bis high (bis or too low. etwaetwa 50A 50 consistently m m von von der der high Schallquelle) Schallquelle) recording erreichbarquality erreichbar must ist. beist. ensured while taking the hydrographic and nautical conditions of the area into account. InIn Tabelle Tabelle 1 1sind sind Empfehlungen Empfehlungen (schwarze (schwarze Zahlen Zahlen im im Fettdruck) Fettdruck) für für die die max. max. zulässige zulässige Schiffsgeschwindigkeit in Abhängigkeit der gewählten Reichweite angegeben. In kursiver SchiffsgeschwindigkeitRange (m) in Abhängigkeit der gewähltenRecommended Reichweite max. angegeben.vessel speed In (kn) kursiver SchriftSchrift sind sind zu zu hohe hohe oder oder zu zu niedrige niedrige Geschwindigkeit Geschwindigkeitenen gekennzeichnet gekennzeichnet.. Es Es ist ist auf auf eine eine gleichbleibendgleichbleibend hohe hohe Aufnahmequalität AufnahmequalitätSingle unter unter pulse Berücksichtigung Berücksichtigung der der hydrographischen hydrographischenMulti-pulse und und nautischen Revierbedingungen zu achten. nautischen Revierbedingungen zu achten. 2 pulses 3 pulses 25 14.6 29.2 43.7 Tabelle 1: Beispiele für die max. zulässige Schiffsgeschwindigkeit in Abhängigkeit der gewählten Tabelle 1: Beispiele35 für die max. zulässige10.4 Schiffsgeschwindigkeit in20.8 Abhängigkeit der gewählten31.2 Reichweite,Reichweite, um um die die geforderte geforderte Auflösung Auflösung von von 0,25 0,25 m m in in Fahrtrichtung Fahrtrichtung zu zu gewährleisten. gewährleisten. 50 7.3 14.6 21.9 ReichweiteReichweite (m) (m) RichtwertRichtwert für für max. max.SchiffsgeschwindigkeitSchiffsgeschwindigkeit (kn) (kn) 75 EinzelpulsEinzelpuls 4.9 Multipuls9.7Multipuls 14.6 2 Pulse 3 Pulse 100 3.6 2 Pulse 7.3 3 Pulse 10.9 25 14,6 29,2 43,7 25 150 14,6 2.4 29,2 4.9 43,7 7.3 35 10,4 20,8 31,2 35 200 10,4 1.8 20,8 3.6 31,2 5.5 50 7,3 14,6 21,9 50 300 7,3 1.2 14,6 2.4 21,9 3.6 75 4,9 9,7 14,6 75 400 4,9 0.9 9,7 1.8 14,6 2.7 100100 3,63,6 7,37,3 10,910,9 Table 1: Examples of the max. allowable vessel speed depending on the selected range to ensure the required resolution of 1501500.25 m in the along-track direction.2,42,4 4,94,9 7,37,3 200200 1,81,8 3,63,6 5,55,5 300300 1,21,2 2,42,4 3,63,6 400400 0,90,9 1,81,8 2,72,7

TabelleTabelle 2: 2: Beispiele Beispiele für für die die max. max. zulässige zulässige Schiffsgeschwindigkeit Schiffsgeschwindigkeit in in Abhängigkeit Abhängigkeit der der gewählten gewählten Reichweite,Reichweite, um um die die geforderte geforderte Auflösung Auflösung von von 1 1m m in in Fahrtrichtung Fahrtrichtung zu zu gewährleisten. gewährleisten.

1515 14 Instructions, Data acquisition

Range (m) Recommended max. vessel speed (kn) Single pulse Multi-pulse 2 pulses 3 pulses 50 29.2 58.3 87.5 75 20.8 41.7 62.5 100 14.6 29.2 43.7 150 9.7 19.4 29.2 200 7.3 14.6 21.9 300 4.9 9.7 14.6 400 3.6 7.3 10.9

Table 2: Examples of the max. allowable vessel speed depending on the selected range to ensure the required resolution of 1 m in the along-track direction.

The effects caused by pycnoclines are to be avoided by using a suitable towing configuration. In such cases a range of 50 to max. 100 m is recommended.

Figures 5 and 6 contain the diagrams for determining an appropriate combination of range and vessel speed for a resolution of 0.25 m and 1 m in the along-track direction.

The determation of the line spacing for the respective study area is depending on the width of the swath (see section 4.1). Maximum allowable vessel speed (knots) Maximum allowable vessel speed (knots)

Fig. 5: Fig. 6: Diagram for determining an appropriate combination of Diagram for determining an appropriate combination of range (x-axis = distance in meters) and max. speed (knots) range (x-axis = distance in meters) and max. vessel speed (= y-axis) for a resolution of 0.25 m in the along-track direc- (knots) (= y-axis) for a resolution of 1 m in the along-track tion. direction. Instructions, Data acquisition 15

During data aquisition, it is important to set the amplification of the backscatter signals (gain) to a fixed value at the beginning of the cruise, if possible. This value can be determined by recording a test profile in the reference area at the beginning of the cruise. For the subsequent data collection, it must be taken into account that changes in the position of the towfish due to varying currents or after a change of direction can have an effect on the quality of the data. The use of automatic gain adjustment is (strongly) inadvisable unless the recording software allows the raw data to be stored separately without automatically adjusting the level of amplification of the signal. The settings must be documented.

During the data collection, it is also necessary to record the distance between the satellite antenna and the pulley as well as the length of the cable between the pulley and the towfish (for example using a counter on the pulley). Based on these minimum specifications, the offset of the towfish relative to the satellite antenna (“layback”) is to be calculated and taken into account for the geometric correction of the data when creating the backscatter mosaic. The procedure used for correction must reproducibly be described in sufficient detail.

Underwater navigation systems can also be used as an alternative (see section 4.2.4).

4.2.2 Sediment samplers

Grab samplers or box corers can be used.

On the basis of expert knowledge, sampling stations are determined based on an initial backscatter mosaic processes on board and, if applicable, including other information available such as the already existing sediment distribution maps for the German marine waters (Laurer et al., 2013; Tauber, 2012). At least one sample per station must be taken. If the first sampling fails, then a maximum of three attempts should be performed and documented. The stations may not be any more than 50 m from the target position. The location of the sediment station must be documented by a precise recording of the actual position of the vessel when the sediment sampler hits the seafloor.

The expert describes and samples the surface of the sediment in a manner that ensures the interpretation of the hydroacoustic data (i. e. this interpretation comprises the correlation of the hydroacoustic data and the grain size classes at the sediment surface).

Each sample successfully taken with the grab sampler is documented via a macroscopic analysis and at least one photo including an indication of the scale (section 4.3).

The determination of the grain sizes is performed in a lab using dry sieving as the standard method. Laser particle size analysis or a sedimentation balance can also be used as an alternative. The method of grain size analysis must be documented in the metadata. 16 Instructions, Data acquisition

In addition to information on the presence of carbonates und organic material (e.g. wood residues) the granulometric data should not comprise less than the following fractions: • < 63 µm (silt and clay), • 63 to < 2000 µm (sand), and • ≥ 2000 µm (gravel and coarser material).

In order to classify German North Sea sands according to Figge (1981), the following sand fractions must be present: • 63 to < 250 µm, • 250 to < 500 µm and • 500 to < 2000 µm.

4.2.3 UW camera (video)

Manually operated drop cameras as well as ROV-mounted UW cameras can be used to visually describe and analyse the sediment types and seabed features according to DIN EN 16260.

The position of the manually operated drop camera is generally determined based on the position of the vessel. The positioning of the ROV-mounted UW camera principally takes place using a hydroacoustic positioning unit. Depending on the water depth and the current conditions, the uncertainty in the accuracy of the positions is approximately 30 m for manually operated drop cameras and 5 to 10 m for ROV-mounted cameras connected to a differential GPS.

When using a manually operated drop camera, the drift velocity should be kept as low as possible (max. 1 knot over the ground). In the North Sea, ROVs should generally be used at slack water times for manoeu- vrability and visibility reasons.

If the coordinates cannot be stored together with the corresponding video images, then timestamps can be used for the purpose of referencing. For video profiles, a minimum of the start and end coordinates must be documented.

The standing time or observation period of the UW camera as well as length of the profile of each video sequence must be defined depending on the results of the side-scan sonar survey and the hydrographic conditions prevailing at the time of usage (for example the swell, direction of the current, turbidity of the water near the bottom, etc.).

4.2.4 Other equipment

Standardly, hull-mounted sounders (single-beam echo sounders or multibeam echo sounders) are used to survey the topography of the seafloor.

The correct positioning is achieved by using the available systems, preferably differential GPS with the appropriate reference stations. The coordinates are continuously recorded as LAT/LON (WGS 84) data.

In addition, underwater navigation systems (ultra short baseline, USBL) can be used for the precise positioning of towed side-scan sonar systems. Instructions, Data acquisition 17

4.3 Documentation of the work at sea

For the documentation of the work done at sea cruise reports and logs must be created, which at least should contain the following information: • Name of the expert (person keeping records); • Name of the vessel and leg number or name of the expedition; • Specification of study area including corner coordinates and a map of the study area; • Period of time; • Scope and tasks of the cruise; • Cruise report with a description of the external conditions (e. g. weather and swell conditions, algae blooms, stratification of the water column) that may effect in the quality of the data; • Equipment list and documentation of the selected settings; • Map illustrating the positions of hydroacoustic profiles, UW video profiles, grab sampler and UW- video camera stations; • Preliminary results (summary); • Appendices with start and end coordinates (and corresponding times) of the hydroacoustic profiles and UW video profiles, as well as the positions of grab sampler and UW video camera stations.

The logs of the grab samples must contain at least the following information: • Name of the ship and leg number or name of the expedition; • Type of grab sampler; • Study area; • Name and numbers of samples; • Coordinates of the stations (LAT/LON based on WGS 84); • Date and time (with LT or UTC specification); • Depth range where samples were taken; • Description of the sample: Primary and secondary components, comments regarding admixtures, shell detritus content, stratification, compactness, smell of H2S, benthos; • Photographic documentation.

An example of a log like those used at the FTZ (Research and Technology Centre, West Coast) can be found in Appendix 3. 18 Instructions, Processing of backscatter data

5 Processing of backscatter data

The following working steps are required at a minimum: • Detection of the first signal from the seabed (bottom tracking); • Processing of the acoustic amplification of the backscatter signals to optimize the signals; • Correction of the geometric offset (correction of the layback, see section 4.2.1); • Export of the mosaic in the GeoTiff format with a spatial resolution of 1 m as the standard specification for mapping sediment types; • Export of the mosaic in the GeoTiff format with a spatial resolution of 0.25 m for sections with special structures like fields of stone or boulders or similar structures; to keep the effort for the processing and evalua- tion of the resulting enormous amount of data within reasonable limits (see section 4.2.1).

Additional methods for image enhancement can be applied; e.g. elimination of the nadir (Wilcken et al., 2012) or other image artefacts (see the hydroacoustic catalogue, Chapter 7).

The backscatter mosaics are to be created as grid data in the following format: • Spatial resolution of 1 m and 0.25 m (see section 4.2.1); • UTM map projection in the corresponding zone (31 N, 32 N, or 33 N); • Geodetic reference system: WGS 84; • Colour depth: 8-bit grey-scale image, whereby 0 represents the highest backscatter and 254 the lowest backscatter; • The colour of the grid cells containing no data is to be set to the colour value 255 (colour= snow white); • Format: GeoTiff. Instructions, Data interpretation 19

6 Data interpretation

6.1 Preliminary remarks and definitions

According to Jackson & Richardson (2007), the frequency-dependent backscatter signal is influenced by the roughness and heterogeneity of the seafloor, the acoustic penetration depth into the seafloor and the hydromechanical properties of the water column.

The roughness and heterogeneity of the seafloor are the result of the interaction between hydrodynamic processes and the properties of the sediments, of the geological structure and of the surface of the seafloor as well as the result of the influence of biological colonization on the seafloor. Furthermore, the roughness of the seafloor can also be influenced by human intervention such as bottom trawl fishing without necessarily leading to a change in the material.

The hydromechanical properties are essentially determined by the density conditions which depend on temperature, salinity, currents and swells.

All of these properties must be taken into account when the expert is interpreting the backscatter mosaics.

The term “sediment types” as used here describes the sedimentological characteristic of a spatially defina- ble area within a backscatter mosaic. The sediment type is usually composed of a mixture of different grain classes. The clastic sediment types are classified based on the system developed by Udden (1914) and Wentworth (1922) commonly used in the marine geosciences and are named according to the system of Blott & Pye (2001, see Appendix 4). An overview of the grain size classes is provided in Appendix 4. The sediment types, spatially delimited on the basis of the backscatter mosaics, are named by reference to the sediment classification of grab samples and UW video recordings according to Folk (1954) and - for the North Sea sands - Figge (1981). The grab samples and the UW video recordings are obtained from the same polygon area. In the case of small-scale, heterogeneous sediment distributions this information can also be used for adjacent areas having the same hydroacoustic texture, whereby the samples should be taken during the same survey.

The term “seabed feature” as used here describes a morphological structure or shape on the seafloor such as ripples, pockmarks as well as outcrops of peat or consolidated mud. Seabed features are defined separately from the sediment types.

6.2 Data basis for the interpretation

The spatial delineation of sediment types is performed based on the processed backscatter mosaics with a resolution of 1 m.

The spatial delineation of fields of stone or boulders or solitary structures (such as individual boulders, for example) is performed on the basis of mosaics with a resolution of 0.25 m (see Chapter 5).

For the purpose of data interpretation the acoustic backscatter patterns within the mosaics must be combined and evaluated with additional data.

This additional data includes the following: • Information from the raw data in the “waterfall mode” (e. g. small-scale seabed features that are not visible any more in the processed mosaic) 20 Instructions, Data interpretation

• UW video recordings (e. g. to ensure the detection and correct determination of stones, boulders, seabed features or epibenthic structures) • Macroscopic description of the sediment samples (including photographic documentation) • Granulometric data • If necessary, information on any epibenthic habitats.

Furthermore, existing information such as the following should be included: • Sediment distribution maps (e.g. Laurer et al., 2013; Tauber, 2012) • Relevant publications and reports

Part B “Hydroacoustic catalogue for the German sea areas” is available as an interpretation aid for the acoustic backscatter patterns.

6.3 Basic specifications

Since there is still a need for the development of standardized approaches for the interpretation of backscatter mosaics using classification software, the specifications for the spatial delineation of sediment types and seabed features in this version of the mapping guideline are initially intended for a visual/manual interpretation by an expert. The use of classification software currently serves as an additional and optional interpretation aid for the visual/manual interpretation. Those results must be compared to the results of the visual/manual interpretation by an expert.

The digitalization at the computer screen should be carried out at a scale of 1 : 10 000. At this scale, the deviation between the digitized outlines (borders between the sediment types) and the structures within the backscatter mosaic is no greater than 20 m, although this is an approximate value. If necessary (for example in the case of very large or very small structures), the digitization can be performed at a larger or smaller scale.

The minimum size of a linear structure or area to be digitized is determined by its longest axis. For the digitization as a discrete feature in the map, the diameter or length of its longest border should be at least 100 m. A larger number of smaller structures located next to each other can be combined into one structure.

6.4 Sediment types

The sediment type polygons, that are delineated based on the backscatter mosaic are classified at four different levels (Table 3) which are described in the following. This level of detail within the classification ensures that: • As many delineated areas as possible in the backscatter mosaic can be assigned to a sediment type • Areas, for which up-to-date granulometric data is available from grab samples, can be classified more precisely • The classification is consistent for geoscientific reasons by ensuring that organogenic or facies sediment types are not mixed with clastic sediment types.

The sediment types in Level A include fine sediment, sand, mixed sediment, coarse sediment and peat. These clastic sediment types represent a simplified classification according to Folk (1954) (Figure 7) to ensure that as many areas as possible can be classified based on a backscatter mosaic. In cases where this is impossible, the term “not specified” can be used in this level as well as in the other levels. Instructions, Data interpretation 21

In Level B the clastic sediment types from Level A (fine sediment, sand, mixed sediment and coarse sediment) are further subdivided according to Folk (1954); provided that the granulometric data basis and the expert knowledge are sufficient for this further classification. Accordingly, the sediment types of Level B are mud, sandy mud, muddy sand, gravelly mud, gravelly muddy sand, muddy gravel, muddy sandy gravel, gravel, sandy gravel and gravelly sand. The sediment type “sand” in Level A corresponds to the “sand” type in Level B, which according to Folk (1954) cannot be subdivided any further.

Provided that the granulometric data basis and the expert knowledge are sufficient, sands in the North Sea are classified – according to Figge (1981) – inLevel C into fine sand, medium sand, mixed sand, and coarse sand (cf. also Ricklefs et al., 2015). For these sand types, the weight percentage of the grain size fractions 63 to < 250 µm, 250 to < 500 µm and 500 to < 2 000 µm are based only on the sand fraction and are classified according to Figge (1981) (Figure 7).

In individual cases, the clastic sediment types can be further classified inLevel D based on more extensive geoscientific interpretations in terms of their facies or how they were formed. Thereby, it is possible to further subdivide the sediments into the types consolidated mud, gyttja, lag sediment (= coarse sediment with stones and boulders), shell pavement and till. This further nomenclature requires expert knowledge of the regional geology and palaeography.

Level A Level B Level C Level D Part B Cat. Nr. consolidated mud, not specified not classified Gyttja Fine Sediment Mud (M) 1 (FSed) sandy Mud (sM) not classified not specified muddy Sand (mS) 2, 22, 23 not classified fine Sand (fSa) 3, 4, 6, 10, 24 medium Sand Sand (S) Sand (S) not specified 4, 5, 7, 16, 17, 20 (mSa) mixed Sand (mxSa) coarse Sand (cSa) 6, 7, 20, 21 Lag sediment not specified not classified (LagSed), shell 13, 15 Coarse Sediment pavement (CSed) gravelly Sand (gS) 8 sandy Gravel (sG) not classified not specified 9 Gravel (G) 10 not specified not classified Till gravelly Mud (gM) gravelly muddy Mixed Sediments Sand (gmS) (MxSed) not classified not specified muddy sandy Gravel (msG) muddy Gravel (mG) Peat not classified not classified not specified 14 not specified not specified not specified not specified

Table 3: The four levels of classification in high-resolution sediment maps of the German North Sea and Baltic Sea. A detailed description of the entries in the attribute tables of the Shelf Geo-Explorer of the BSH can be found in Appendices 5 and 6.

Not specified = Lack of information and/or knowledge for the exact classification Not classified = Cannot be classified further in this level 22 Instructions, Data interpretation y system from Folk (1954) for the German sea areas. Right: Sand types I to IV according to the Sand types I to IV according Right: the German sea areas. Folk (1954) for y system from Left: Clastic sediment types according to the simplified ternar Clastic sediment types according Left: ternary system from Figge (1981) applied only in the German North Figge (1981) applied only Sea. ternary system from

Fig. 7: 7: Fig. Abbreviations: Classification according to Folk (1954) – M = Mud, sM = sandy Mud, mS = muddy Sand, S= Sand, gM = gravelly Mud, gmS = gravelly muddy Sand, gS = Sand, muddy gmS = gravelly Mud, gM = gravelly S= Sand, Sand, mS = muddy Mud, sM = sandy to Folk (1954) – M = Mud, Classification according Abbreviations: sand (1981) – sand type I = fine sand, to Figge Classification according G = Gravel. Gravel, sG = sandy Gravel, sandy msG = muddy Gravel, mG = muddy Sand, gravelly sand. sand type IV = coarse sand, sand type III = mixed type II = medium sand, Instructions, Data interpretation 23

6.5 Special cases

If it is impossible to differentiate between two or more sediment types in the acoustic backscatter mosaics because

(I) their acoustic values are not distinguishable or (II) their spatial changes appear at a very small scale (< 100 m), then the labels “+” (and) and “–” (to) in Table 4 are to be used. Figure 8 shows an example of their usage. Appendix 6 contains examples of their application in the database of the Shelf Geo-Explorer of the BSH.

Symbol Meaning Explanation - to Case (I): It is impossible to differentiate further between the sediment types in the backscatter mosaic. Depending on the properties of the seafloor (e. g. roughness, morphology, colonies of epibenthic organisms) a given sediment type may show different backscatter properties or different sediment types may show similar backscatter properties. For this reason, it is not always possible to clearly differentiate the respective sediment types in a backscatter mosaic from each other (see Figure 8). This is indicated by the prep- osition “to” (e. g. fine to medium sand, abbreviation “fSa - mSa”) + and Case (II): In the backscatter mosaic, the area shows a small-scale, heterogeneous texture. Due to of the processing scale (1 : 10 000) and the minimum size of the structures to be digitized (100 m, see section 6.3) not all areas with small-scaled structures will be digitized as discrete features in the map. In case of small-scaled textural changes, the structures will be digitized individually, if they are at least 100 m apart from each other. If this minimum distance is not given in highly heterogeneous areas, then the textures are combined into a “heterogeneous texture” (see Figure 8). The respective sediment types are combined using the conjunction “and” (abbreviation “+”, e. g. “mSa + fSa”). If possible, the predominant sediment type is named first. Table 4: Special cases. 24 Instructions, Data interpretation

Abb. 8: Exemplary illustration for special cases and spatial delineation of sediment types.

6.6 Types of stone and boulder fields

(to be completed)

6.7 Seabed features

(to be completed)

6.8 Bedrock

(to be completed) Instructions, Data interpretation, Work flow 25

6.9 Other

It is not always possible to clearly identify the boundaries between the sediment types defined in this guideline. Gradual transitions lead to uncertainties in the spatial delineation of sediment types and can therefore vary depending on the person analysing the image and creating the map. For this reason, the borders around the sediment types are either marked as a “distinct boundary” (solid line) or “uncertain boundary” (dashed line) to assess the quality of the spatial delineation (see Fig. 8). These boundaries are drawn starting with a minimum line length of 100 m, analogous to the minimum size of the structures to be digitized.

Solitary features like pockmarks or very large, individual stones are digitized as dots.

7 Work flow

Figure 9 illustrates the methods, data flows and working steps required to obtain a sediment type distribution with high spatial resolution.

Fig. 9: Flow chart for mapping sediment types. 26 Instructions, Products

8 Products

The final product comprises a combined set of maps consisting of polygons (sediment types, types of fields of stones and boulders, seabed features, bedrock) and lines (boundaries, seabed features) as well as dots (solitary structures). Together with the backscatter mosaic (see Chapter 5) this dataset represent all availabe information of the data aquired (Table 5).

Product Shape Attribute Sediment types Polygon Identifier (see Table 3 as well as Appendix 5 and 6) Types of stone and boul- Polygon Number of detectable boulders in the mosaic der fields Seabed features Polyline or polygon Identifier Bedrock Polygon Identifier Boundaries Polyline Type of boundary (1=uncertain, 2=distinct) Solitary features Polypoint Identifier Table 5: The individual types of information provided in the digital map.

The shape files are to be produced using the following projection: • UTM in the corresponding zone (31 N 32 N or 33 N based on the geodetic reference WGS 84). Instructions, Bibliography 27

9 Bibliography

Baker, E. K., Harris, P. T., 2012. Habitat Mapping and Marine Management. In: Harris, P. T., Baker, E. K. (publisher): Seafloor Geomorphology as Benthic Habitat. GeoHab Atlas of Seafloor Geomorphic Features and Benthic Habitat. Elsevier, 23–38. Blondel, P., 2009. Handbook of Sidescan Sonar. Springer, 316 pp. Blondel, P., Murton, B. J., 1997. Handbook of Seafloor Sonar Imagery. Wiley, 314 pp. Blott, S. J., Pye, K., 2001. GRADISTAT: a Grain Size Distribution and Statistics Package for the Analysis of Uncon- solidated Sediments. Earth Surface Processes and Landforms, 26, 1237–1248. Coggan, R., Populus, J., White, J., Sheehan, K., Fitzpatrick, F., Piel, S., 2007. Review of Standards and Protocols for Seabed Habitat Mapping. MESH, 203 pp. Figge, K., 1981. Sedimentverteilung in der Deutschen Bucht (Sediment distribution in the German Bight) (sheet no. 2900, scale 1 : 250,000). German Hydrographic Institute, Hamburg. Folk, R. L., 1954. The Distinction between Grain Size and Mineral Composition in Sedimentary-Rock Nomenclature. Journal of Geology, 62, 344–359. Folk, R. L., und WARD, W. C., 1957: Brazos River bar: a study in the significance of grain size parameters. In: Jour- nal of Sedimentary Petrology, 27, 3-26. Friedman, G. M., Sanders, J. E., 1978. Principles of Sedimentology. Wiley, 808 pp. Gerwick, B. C., 2007. Construction of Marine and Offshore Structures, CRC Press, 840 pp. Harris, P. T., Baker, E. K., 2012. Why map Benthic Habitats? In: Harris, P. T., Baker, E. K. (publisher): Seafloor Ge- omorphology as Benthic Habitat. GeoHab Atlas of Seafloor Geomorphic Features and Benthic Habitat. Elsevier, 3–22. Heyer, H., Schrottke, K., 2013. AufMod – Aufbau von integrierten Modellsystemen zur Analyse der langfristigen Morphodynamik in der Deutschen Bucht (Development of integrated model systems for the analysis of long-term morphodynamics in the German Bight). Combined final report for the overall project with contributions from all 7 subprojects, 292 pp. (available only in German) Holler, P., Bartholomä, A., 2014. Akustische Seebodenklassifikation in der südlichen Nordsee – Variabilität in der akustischen Abbildung großräumiger Sedimenttypenmuster in der deutschen AWZ – ASKAWZ (Acoustic seafloor classification in the southern North Sea – Variability in the acoustic mapping of large-scale sediment type patterns in the German EEZ – ASKAWZ). Final report of the Senckenberg-Gesellschaft für Naturforschung (Senckenberg Natural Research Society), Senckenberg am Meer, 45 pp. (available only in German) Jackson, D. R., Richardson, M. D., 2007. High-Frequency Seafloor Acoustics. Springer, 616 pp. Johnson, H. P., Helferty, M., 1990. The Geological Interpretation of Side-Scan Sonar. Reviews in Geophysics, 28, 357–380. Kenny, A. J., Cato, I., Desprez, M., Fader, G. B., Schuttenhelm, R. T. E., 2003. An Overview of Seabed-Mapping Technologies in the Context of Marine Habitat Classification. ICES Journal of Marine Science, 60, 411–418. Laurer, W.-U., Naumann, M., Zeiler, M., 2013. Sedimentverteilung in der deutschen Nordsee nach der Klassifikation von Figge (1981) (Sediment distribution in the German North Sea, classification according to Figge (1981). http:// www.gpdn.de. (available only in German) Lurton, X., 2010. An Introduction to Underwater Acoustics. Springer, 724 pp. Papenmeier, S., Hass, H. C., 2014. Akustische Meeresbodenklassifikation in der Nordsee – Sedimentdynamik im küstenfernen Milieu - AMIN I (Acoustic seafloor classification in the North Sea – Sediment dynamics in the offshore environment - AMIN I. Final report of the Alfred Wegener Institute for Polar and Marine Research, Wadden Sea Station Sylt, 21 pp. (available only in German) Poulos, H. G., 1988. Marine Geotechnics. Spon Press, 512 pp. Richter, P. P., Schwarzer, K., 2014. Entwicklung eines standardisierten Verfahrens zur flächendeckenden Erfassung und Beschreibung sedimentologischer Eigenschaften und Prozesse auf der Meeresbodenoberfläche in der aus- schließlichen Wirtschaftszone (AWZ) von Nord- und Ostsee, Teilprojekt SEDINO (Development of a standardized 28 Instructions, Bibliography

method for the full coverage mapping and description of sedimentological properties and processes on the surface of the seafloor in the Exclusive Economic Zone (EEZ) of the North and Baltic Sea, subproject SEDINO). Final report of the Institute of Geosciences of the University of Kiel, 53 pp. (available only in German) Ricklefs, K., Arp, D., Stage, M., 2015. Zur zeitlichen Variabilität der Sedimentverteilungen in den Gezeitenrinnen Piep und Hever (On the variability over time of the sediment distributions in the Piep and Hever tidal channels). Die Küste, 50. (available only in German) Schwarzer, K., Diesing, M., 2006. Erforschung der FFH-Lebensraumtypen Sandbank und Riff in der AWZ der deutschen Nord- und Ostsee (Study of the sandbank and reef FFH habitat types in the EEZ of the German North Sea and Baltic Sea). Final report, 69 pp. (available only in German) Schwarzer, K., Heinrich, C., Papenmeier, S., 2014a. Identifikation mariner Lebensraumtypen in der Mecklenburger Bucht (Identification of marine habitat types in the Mecklenburg Bay). Final report of the Institute of Geosciences of the University of Kiel, 39 pp. (available only in German) Schwarzer, K., Heinrich, C., Feldens, P., 2014b. Identifizierung mariner Lebensraumtypen in der Kieler Bucht west- lich Fehmarn (Identification of marine habitat types in the Bay of Kiel west of Fehmarn). Final report of the Institute of Geosciences of the University of Kiel, 24 pp. (available only in German) Storlazzi, C. D., Fregoso, T. A., Figurski, J. A., Freiwald, J., Lonhart, S. I., Finlayson, D. P., 2013. Burial and Exhu- mation of Temperate Bedrock Reefs as Elucidated by Repetitive High-Resolution Sea Floor Sonar Surveys: Spatial Patterns and Impacts to Species’ Richness and Diversity. Continental Shelf Research, 55, 40–51. Tauber, F., 2012. Seabed sediments in the German Baltic Sea: Adlergrund, Map No. 2938. Scale 1 : 100 000. Pub- lished by the Federal Maritime and Hydrographic Agency. www.bsh.de/de/Produkte/Karten/Geologische_Karten/ index.jsp. (available only in German) Tauber, F., 2012. Seabed sediments in the German Baltic Sea: Arkona, Map No. 2936. Scale 1 : 100 000. Published by the Federal Maritime and Hydrographic Agency. www.bsh.de/de/Produkte/Karten/Geologische_Karten/index. jsp. (available only in German) Tauber, F., 2012. Seabed sediments in the German Baltic Sea: Darß – Hiddensee, Map No. 2935. Scale 1 : 100 000. Published by the Federal Maritime and Hydrographic Agency. www.bsh.de/de/Produkte/Karten/ Geologische_ Karten/index.jsp. (available only in German) Tauber, F., 2012. Seabed sediments in the German Baltic Sea: Fehmarn, Map No. 2932. Scale 1 : 100 000. Published by the Federal Maritime and Hydrographic Agency. www.bsh.de/de/Produkte/Karten/Geologische_Karten/index. jsp. (available only in German) Tauber, F., 2012. Seabed sediments in the German Baltic Sea: Bay of Kiel – Flensburg Fjord, Map No. 2931. Scale 1 : 100 000. Published by the Federal Maritime and Hydrographic Agency. www.bsh.de/de/Produkte/Karten/Geolo- gische_Karten/index.jsp. (available only in German) Tauber, F., 2012. Seabed sediments in the German Baltic Sea: Bay of Lübeck – Bay of Mecklenburg, Map No. 2933. Scale 1 : 100 000. Published by the Federal Maritime and Hydrographic Agency. www.bsh.de/de/Produkte/Karten/ Geologische_Karten/index.jsp. (available only in German) Tauber, F., 2012. Seabed sediments in the German Baltic Sea: Bay of Mecklenburg – Darß, Map No. 2934. Scale 1 : 100 000. Published by the Federal Maritime and Hydrographic Agency. www.bsh.de/de/ Produkte/Karten/Geol- ogische_Karten/index.jsp. (available only in German) Tauber, F., 2012. Seabed sediments in the German Baltic Sea: Pomeranian Bay, Map No. 2939. Scale 1 : 100 000. Published by the Federal Maritime and Hydrographic Agency. www.bsh.de/de/Produkte/Karten/Geologische_ Karten/index.jsp. (available only in German) Tauber, F., 2012. Seabed sediments in the German Baltic Sea: Rügen – Usedom, Map No. 2937. Scale 1 : 100 000. Published by the Federal Maritime and Hydrographic Agency. www.bsh.de/de/Produkte/Karten/Geologische_ Karten/index.jsp. (available only in German) Udden, J. A., 1914. Mechanical Composition of Clastic Sediments. Bulletin of the Geological Society of America, 25, 655–744. Wentworth, C. K., 1922. A Scale of Grade and Class Terms for Clastic Sediments. Journal of Geology, 30, 377–392. Wilcken, D., Feldens, P., Wunderlich, T., Heinrich, C., 2012. Application of 2D Fourier Filtering for Elimination of Stripe Noise in Side-Scan Sonar Mosaics. Geo-Marine Letters, DOI 10. 1007/s00367-012-0293-z. Instructions, Standards and guidelines 29

10 Standards and guidelines

EN 16260:2012. Water quality – Visual seabed surveys using remotely operated and/or towed observation gear for collection of environmental data. ICES, 2007. Acoustic Seabed Classification of Marine Physical and Biological Landscapes. ICES Cooperative Re- search Report, 286, 185 pp. (http://www.ices.dk/community/groups/Pages/WGMHM.aspx) IHO, 2008. IHO Standards for Hydrographic Surveys. Special Publication No. 44. 5th Edition, Monaco. Lekkerkerk, H.-J., Theijs, M. J., 2011a. Handbook of Offshore Surveying. Volume 1 – Projects, Preparation and Processing. www.skilltradebookstore.nl, 232 pp. Lekkerkerk, H.-J., Theijs, M. J., 2011b. Handbook of Offshore Surveying. Volume 2 – Positioning and Tides. www.skilltradebookstore.nl, 240 pp. Lekkerkerk, H.-J., Theijs, M. J., 2011c. Handbook of Offshore Surveying. Volume 3 – Acquisition Sensors. www.skilltradebookstore.nl, 224 pp. Lurton, X., Lamarche, G., 2015. Backscatter Measurements by Seafloor-Mapping Sonars. Guidelines and Recom- mendations. A Collective Report by Members of the GeoHab Backscatter Working Group. 200 pp. (https://www.niwa.co.nz/static/backscatter_measurement_guidelines.pdf) Mazel, C., 1985: Side Scan Sonar Training Manual. Klein Associates, Inc. MESH Project, 2008. MESH Guide to Habitat Mapping. Joint Nature Conservation Committee, Peterborough, UK. (http://www.emodnet-seabedhabitats.eu) 30 Instructions, Abbreviations and acronyms

11 Abbreviations and acronyms

AWI Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research BALANCE Baltic Sea Management – Nature Conservation and Sustainable Development of the Ecosystem through Spatial Planning (2005 to 2007) BfN German Federal Agency for Nature Conservation BGR German Federal Institute for Geosciences and Natural Resources CAU Christian Albrecht University of Kiel CEFAS Centre for Environment, Fisheries & Aquaculture Science FFT Fast Fourier Transform GPDN Geopotential of the German North Sea GPS Global Positioning System HELCOM Baltic Marine Environment Protection Commission – Helsinki Commission ICES International Council for the Exploration of the Sea IHO International Hydrographic Organization IOW Leibniz Institute for Baltic Sea Research LAT Geographical latitude LBEG State Office for Mining, Energy and Geology (Lower Saxony) LONG Geographic longitude LT Local time SDI-DE Sea Data Infrastructure Germany MESH Mapping European Seabed Habitats (2004 to 2010) MSFD Marine Strategy Framework Directive ROV Remotely Operated Vehicle SaM Senckenberg am Meer USBL Ultra Short Baseline (underwater navigation system) UTC Coordinated Universal Time UW Underwater WGMHM Working Group Marine Habitat Mapping WGS World Geodetic System WFD Water Framework Directive Instructions, Appendix 1 31

Appendix 1

Sediment distribution in the German North Sea, classification according to Figge (Laurer et al., 2013). 32 Instructions, Appendix 2

Appendix 2

Sediment distribution in the German Baltic Sea, classification according to Tauber (2012). Instructions, Appendix 3 33

Appendix 3

Example of a log to describe sediment samples. Source: K. Ricklefs (Research and Technology Centre West Coast of the University of Kiel).

Date: Time: Sample number:

Water depth (m): Filling level of the sediment sampler (%):

Turbidity of supernatant water: Sample depth (cm): none weak Depth of reduction horizon (cm): noticeable strong

Sediment description

Primary component stones Secondary component (not specified) gravel rocky very coarse coarse sand strong gravelly coarse medium sand (not specified) coarse sandy (not specified) fine sand weak medium fine silt sandy very fine mud fine sandy clay silty consolidated mud muddy till clyey gyttja containing peat

Admixtures medium sand till fine sand gyttja (not specified) silt peat stones mud gravel clay coarse sand consolidated mud

Shell content (%): Shell – degree of coverage (%):

Bioturbation: none weak strong

Living benthos: Juvenil Adult Juvenil Adult Mytilus Mya Ostrea Macoma Cardium Arctica Ensis Lanice

Consistency Bulk density Smell of H2S liquidy/pasty very loose very strong pasty loose strong soft medium density noticeable stiff compact weak semi solid very compact very weak solid none

Photo no.: Sample taken?

Comments: 34 Instructions, Appendix 4

Appendix 4

Grain size classes according to the system of Udden (1914) and Wentworth (1922) and the extension of the system by Friedman & Sanders (1978) and Blott & Pye (2001). The designations used in this mapping guide are based on the designations defined by Blott & Pye (2001). Instructions, Appendix 5 35

Appendix 5

Examples of entries in the attribute tables of the Shelf Geo-Explorer of the BSH

Part 1: Sediment types (see Table 3).

D C A B Formation, organogen- North Sea sands: Figge SonarSedType Folk (1954) ic sediments, or other (1981) interpretations Consolidated mud, gyttja FSed 1 NC or others FSed M NC 1 FSed sM NC 1 FSed mS NC 1 S S 1 1 S S fSa 1 S S mSa 1 S S mxSa 1 S S cSa 1 Csed 1 NC LagSed, shell pavement CSed gS NC 1 CSed sG NC 1 CSed G NC 1 MxSed 1 NC Till MxSed gM NC 1 MxSed gmS NC 1 MxSed msG NC 1 MxSed mG NC 1 Peat NC NC 1 1 1 1 1

1 Not specified (Lack of information and/or knowledge for the exact classification) NC Not classified (Cannot be classified further in this level) 36 Instructions, Appendix 6

Appendix 6

Examples of entries in the attribute tables of the Shelf Geo-Explorer of the BSH

Part 2: Combinations of sediment types for special case II – „An area in the backscatter mosaic shows a small-scale, heterogeneous texture“ (Abbreviation „+“, see Table 4). Sediment types printed in bold letters (code) in Level A can be classified more precisely in Level B and C due to adequate available information.

Case I should be edited in the same way – „The sediment types in the backscatter mosaic cannot be differen- tiated further“ (Abbreviation „–“, see Table 4)

D C A B Formation, organo North Sea sands: Figge SonarSedType Folk (1954) genic sediments or (1981) other interpretations FSed + MxSed sM + gmS NC 1 FSed + MxSed sM + 1 NC 1 FSed + MxSed 1 + gmS NC 1 FSed + MxSed 1 NC 1 FSed + S sM + S NC + fSa 1 FSed + S sM + S NC + 1 1 FSed + S 1 + S NC + fSa 1 FSed + S 1 + S NC + 1 1 S S fSa + cSa 1 S S fSa + 1 1 CSed = LagSed or CSed + S 1 + S NC + fSa CSed = LagSed? CSed = LagSed or CSed + S 1 + S NC + 1 CSed = LagSed? CSed = LagSed or CSed + MxSed 1 + gmS NC CSed = LagSed? CSed = LagSed or CSed + MxSed 1 NC CSed = LagSed? Peat + S NC + S NC + fSa 1 Peat + S NC + S NC + 1 1 Peat + MxSed NC + gmS NC 1 Peat + MxSed NC + 1 NC 1 Peat NC NC 1 1 1 1 1

1 Not specified (Lack of information and/or knowledge for the exact classification) NC Not classified (Cannot be classified further in this level) Hydroacoustic Catalogue, Table of Contents 37

Part B – Hydroacoustic Catalogue for the German Marine Waters

1 Table of Contents...... 37

2 Sediment types...... 40

Mud ...... 40 Muddy sand ...... 44 Fine sand ...... 46 Fine sand/Medium sand ...... 50 Medium sand ...... 56 Coarse sand/Fine sand ...... 58 Coarse sand/Medium sand ...... 60 Gravelly sand ...... 62 Sandy gravel ...... 64 Gravel/Stones ...... 66 Stone deposit I ...... 68 Stone deposit II ...... 70 Lag sediment...... 72 Peat ...... 74 Comparison: Gravel/Shells/Medium sand ...... 76

3 Bedrock...... 80

Rocky substrate ...... 80

4 Seabed features – Dynamic sediment structures...... 82

Dunes I ...... 82 Dunes II ...... 84 Ripple structures ...... 86 “Transport bodies” ...... 90 Small-scale facies change ...... 94

5 Biogenic structures...... 96

Sead mussel area (with marks from fishing) ...... 96 Sead mussel area (with spilling marks) ...... 100 Sand in combination with Lanice conchilega ...... 104 38 Hydroacoustic Catalogue, Table of Contents

6 Anthropogenic structures...... 106

Wreck ...... 106 Dredging marks ...... 110 Otter board marks ...... 112 Beam trawls ...... 116 Anchor chain marks ...... 117 Transit pipeline ...... 118 Anchorage ...... 120 Sand dredging ...... 124 Dumped dredge spoil ...... 126 Foundation of a platform ...... 127

7 Artefacts in the water column...... 128

Propeller noise ...... 128 Schools of fish ...... 130 Air bubbles ...... 131 Pycnocline ...... 132 Suspended matter in the water ...... 134

8 Interferences during data recording ...... 136

Acoustic interference ...... 136 Acoustic interference by SES sub-bottom profilers ...... 138 Acoustic interference due to machine noise ...... 140 Acoustic interference – Reflection of the water column ...... 142 Quenching ...... 144 Swell ...... 146 Hydroacoustic Catalogue, Usage information 39

Information on the use of the hydroacoustic catalogue

Hydroacoustic images

In the hydroacoustic images, the dark grey values represent high backscatter intensities and light grey values low backscatter intensities (sea Part A, Chapter 5).

The sampling stations are only shown in the hydroacoustic images when it’s depicting a backscatter mosaic. The specification of the location (coordinates) always refers to the middle of the hydroacoustic image.

Statistical parameters and diagrams of grain size distributions

The statistical parameters were calculated using the GRADISTAT program (Blott and Pye, 2001) according to Folk and Ward (1957).

For some of the following grab samples no upper or lower limits in the grain size distributions are available for methodological reasons. If this is the case, it is indicated in the description of the respective sample.

Legend of symbols

Many images contain arrows to indicate the direction of motion (heading), the northern direction as well as special features.

• Orange arrow = heading

• Blue arrow = northern direction

• Green arrow = special features

40 Hydroacoustic Catalogue, Sediment types

2 Sediment types

Mud

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 100 x 230 m SSE 1

Documentation Description of location (hydroacoustic image) Record date 12 October 2008 DK Conditions during recording calm sea Towing speed (kn) 5 Device type (& brand) Benthos 1624 Frequency (kHz) 400 Gain 9 North Sea DE Processing software SonarWiz Comments: Range = 50 m NL Coordinates: N 53.50848° E 008.17976° Hydroacoustic Catalogue, Sediment types 41

Mud

Photo/video documentation

Description of the image Position of grab sample: N 53.50667° E 008.17835°

Description of the grab sample Mud Grain size distribution (96.48 % Mud, 3.26 % Sand, 0 % Gravel, 0.26 % Mussel shells)

Stat. parameters 1st mode (µm): 2.9 µm Median (µm): 2.0 µm Mean value (µm): 9.8 µm Skewness: 1.91 42 Hydroacoustic Catalogue, Sediment types

Mud

Explanations and supplementary information Additional examples of Mud: This example is adjacent to the previous example (coordinates N 53.50190° E 008.18046°)

Hydroacoustic Catalogue, Sediment types 43

Mud

Explanations and supplementary information Documentation (hydroacoustic image) Display Waterfall Record date 10 March 2005 Image size 160 x 150 m Conditions during recording Heading SO Towing speed (kn) 3.8 Description of Coordinates: location N 54.185° Device type (& brand) EG&G DF-1000 E 011.509° Frequency (kHz) 100 & 384

Gain Processing software Own software (IOW/F. Tauber) Comments: Range = 80 m

Concerning mud, the first echoes from the seafloor (marked in the image by an M) are usually only weak signals and often cannot even be recognized (in contrast to fine sand, compare to catalogue no. 3). P: Ping start W: Echoes from water surface S: Echo from the vessel’s hull M: First echoes from the seafloor 44 Hydroacoustic Catalogue, Sediment types

Muddy sand

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 200 x 300 m SW 2

Documentation Description of location (hydroacoustic image) Record date 11 July 2012 DK Conditions during recording Swell 1.5 m Towing speed (kn) 5 Device type (& brand) Benthos 1624 Frequency (kHz) 400 Gain 9 North Sea DE Processing software SonarWiz Comments: Range = 100 m Slant-range corrected NL Coordinates: N 54.21535° E 007.80506° Hydroacoustic Catalogue, Sediment types 45

Muddy sand

Photo/video documentation

Description of the image Position of grab sample: N 54.21416° Position of video recording: N 54.20725° E 007.80750° E 007.79503°

Description of the grab sample Muddy sand Grain size distribution (original data: lower limit open)

Stat. parameters* 1st mode (µm): 115.0 2nd mode (µm): 0.65 Median (µm): 85.2 Mean value (µm): Coarse silt (23.8)

* The sample is not uni-modal. For this reason, statistical information on the sorting and skew is unreliable and therefore not listed here. 46 Hydroacoustic Catalogue, Sediment types

Fine sand

Hydroacoustic image

Display Image size Heading Catalogue no. Mosaic 9.5 x 17.2 km NE/SW 3

Documentation Description of location (hydroacoustic image) Record date 17 May 2013 DK Conditions during recording calm sea Towing speed (kn) 6.5 Device type (& brand) Edgetech-4200 MP Frequency (kHz) 300 Gain 14 North Sea DE Processing software SonarWIz Comments: Range = 230 m, Slant-range corrected, EGN NL Coordinates: N 54.875° E 006.648° Hydroacoustic Catalogue, Sediment types 47

Fine sand

Photo/video documentation

Description of the image Position of grab sample: N 54.845° E 006.648°

Description of the grab sample Fine sand Grain size distribution (Sample 30)

Stat. parameters 1st mode (µm): 80.9 Median (µm): 76.1 Mean value (µm): Fine sand (66.8) Sorting: Poorly sorted (2.19) Skewness: Very negative skewed (-0.56) 48 Hydroacoustic Catalogue, Sediment types

Fine sand

Explanations and supplementary information Another example of fine sand:

Documentation Display Waterfall (hydroacoustic image) Image size 160 x 180 m Record date 14 Feb. 2007 Heading ONO Conditions during recording Description of Coordinates: Towing speed (kn) 4.6 location N 54.475° E 012.447° Device type (& brand) EG & G DF-1000 Frequency (kHz) 100 & 384 Gain Processing software Own software (IOW/F. Tauber) Comments: Range = 80 m

Concerning sand, the first echo from the seafloor is generally more or less clearly visible while concerning mud the first echo from the seafloor is usually barely detectable (compare to catalogue no. 1).

P: Ping start W: Echoes from water surface M: First echoes from the seafloor

50 Hydroacoustic Catalogue, Sediment types

1 – SEDIMENTTYPEN Vergleich: Feinsand und Mittelsand Fine sand/Medium sand Hydroakustische Aufnahme Hydroacoustic image

1 3

102

Display Image size 1,7 x 2,5 Heading CatalogueKatalog no. - Darstellung Mosaik Bildgröße Fahrtrichtung NE/SW A27 Mosaic 1.7 x 2.5 km km NE/SW 4 Nr.

Documentation Description of location (hydroacoustic image) Record date 17 May 2013 DK Conditions during recording calm sea Dokumentation (hydroakustische Aufnahme) Lagebeschreibung Towing speed (kn) 6.5 Datum der AufnahmeDevice type (& brand)17.05.2013 Edgetech-4200 MP Äußere BedingungenFrequency (kHz) 300 Ruhige See KartenbildNorth Sea bei der AufnahmeGain 14 DE SchleppgeschwindigkeitProcessing software SonarWIz 6.5 (kn) Comments: Range = 230 m, Slant-range corrected Gerätetyp (& Marke) Edgetech-4200 MP NL Coordinates: N 54.96721° Frequenz (kHz) 300 E 006.97116°

Gain 14

Software für Mosaiking SonarWIZ

Bemerkungen

Range 230m Slant range corrected

Koordinaten LAT 54.96721 / LON 6.97116

Hydroacoustic Catalogue, Sediment types 51

Fine sand/Medium sand

Photo/video documentation

Position 102

Description of the image Position of grab sample: N 54.93379° Position of video recording: N 54.9340° E 006.96298° E 006.9620°

Description of the grab sample Fine sand Grain size distribution (Sample 102)

Stat. parameters 1st mode (µm): 185.9 Median (µm): 184.9 Mean value Fine sand (µm): (183.5) Sorting: Moderately well sorted (1.43) Skewness: Almost symmetric (-0.07) 52 Hydroacoustic Catalogue, Sediment types

Fine sand/Medium sand

Photo/video documentation

Position 4

Description of the image Position of grab sample: N 54.96431° Position of video recording: N 54.964° E 006.97464° E 006.974°

Description of the grab sample Medium sand with ripples Grain size distribution (sample 4)

Stat. parameters 1st mode (µm): 302.1 Median (µm): 294.3 Mean value Medium sand (µm): (284.15) Sorting: Moderately well sorted (1.59) Skewness: Very negative skew (-0.31) Hydroacoustic Catalogue, Sediment types 53

Fine sand/Medium sand

Photo/video documentation

Position 3

Description of the image Position of grab sample: N 54.96384° Position of video recording: N 54.963° E 006.99254° E 006.992°

Description of the grab sample Fine sand with ripples Grain size distribution (Sample 3)

Stat. parameters Stat. parameters 1st mode (µm): 302.1 1st mode (µm): 228.9 Median (µm): 294.3 Median (µm): 214.6 Mean value Medium sand Mean value Fine sand (µm): (284.15) (µm): (210.5) Sorting: Moderately well Sorting: Moderately sorted (1.59) well Skewness: Very negative sorted (1.49) skew (-0.31) Skewness: Negative skew (-0.15) 54 Hydroacoustic Catalogue, Sediment types

Fine sand/Medium sand

Photo/video documentation

Position 1

Description of the image Position of grab sample: N 54.96556° Position of video recording: N 54.965° E 007.00876° E 007.008°

Description of the grab sample Fine sand with mussels & starfish, ripples Grain size distribution (Sample 1)

Stat. parameters 1st mode (µm): 151.0 Median (µm): 149.0 Mean value Fine sand (µm): (147.3) Sorting: Moderately well sorted (1.56) Skewness: Negative skew (-0.21) Hydroacoustic Catalogue, Sediment types 55

Fine sand/Medium sand

Explanations and supplementary information The mosaic basically shows two regions with different backscatter intensities: low backscatter values in the east and higher values in the west. The latter region also contains a narrow strip with smaller backscatter signals (NW-SE). Grab samples (102 and 3) show that the lower backscatter intensities represent fine sands. The eastern part of the area with higher backscatter intensities also represents fine sands (grab sample 1) but ripple and epibenthic structures in this area cause a higher backscatter intensity that is com- parable to that of rippled medium sand (sample 4). 56 Hydroacoustic Catalogue, Sediment types

Medium sand

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 300 x 375 m WSW 5

Documentation Description of location (hydroacoustic image) Record date 14 November 2012 DK Conditions during recording calm Towing speed (kn) 5 Device type (& brand) Benthos 1624 Frequency (kHz) 400 Gain 9 North Sea DE Processing software SonarWiz Comments: Range = 150 m NL Coordinates: N 53.95153° E 006.42466° Hydroacoustic Catalogue, Sediment types 57

Medium sand

Photo/video documentation

Description of the image Position of grab sample: N 53.94716° E 006.41987°

Description of the grab sample Medium sand Grain size distribution

Stat. parameters* 1st mode (µm): 460.0 2nd mode (µm): 920.5 Median (µm): 494.9 Mean value Coarse sand (µm): (529.2)

* The sample is not uni-modal. For this reason, statistical information on the sorting and skew is unreliable and therefore not listed here.

Explanations and supplementary information The grab sample shows that the sediment type is medium sand. The sonar image shows a typical backscatter pattern for fine to medium sandy sediments (with relatively low backscatter intensities) and a clear identification of the sediment type would not be possible without ground truthing (here: grab sample). 58 Hydroacoustic Catalogue, Sediment types

Coarse sand/Fine sand

Hydroacoustic image

Display Image size Heading Catalogue no. Mosaic 300 x 450 m N-S 6

Documentation Description of location (hydroacoustic image) Record date 18 September 2014 DK Conditions during recording Wind: E, 5 Bft Towing speed (kn) 5 Device type (& brand) Teledyne Benthos C3D

Frequency (kHz) 200 North Sea DE Gain 7 Processing software SonarWiz

Comments: Range = 100 m NL Coordinates: N 54.78982° E 007.59520° Hydroacoustic Catalogue, Sediment types 59

Coarse sand/Fine sand

Photo/video documentation

Fine sand

Description of the image Position of grab sample: N 54.78972° E 007.59291°

Description of the grab sample Fine sand structures in coarse sediment Grain size distribution

Stat. parameters 1st mode (µm): 196.0 Median (µm): 198.1 Mean value (µm): Fine sand (204.8) Sorting: Well sorted (1.36) Skewness: Positive skew (0.15)

Explanations and supplementary information The mosaic shows small-scaled fine sand structures (diameter: 10–20 m) in the surrounding coarse sediment. 60 Hydroacoustic Catalogue, Sediment types

Coarse sand/Medium sand

Hydroacoustic image

Display Image size Heading Catalogue no. Mosaic 500 x 400 m N-S 7

Documentation Description of location (hydroacoustic image) Record date 12 September 2014 DK Conditions during recording Wind: E, 3 Bft Towing speed (kn) 5 Device type (& brand) Teledyne Benthos C3D

Frequency (kHz) 200 North Sea DE Gain 7 Processing software SonarWiz

Comments: Range = 100 m NL Coordinates: N 55.01494° E 007.66678° Hydroacoustic Catalogue, Sediment types 61

Coarse sand/Medium sand

Photo/video documentation

Coarse sand Medium sand Description of the image Position of grab samplen: N 55.01582° N 55.01396° E 007.66389° E 007.66419° Description of the grab sample Boundary between coarse and medium sand Grain size distribution Coarse sand Medium sand

Stat. parameters* Stat. parameters 1st mode (µm): 925.0 1st mode (µm): 327.5 2nd mode (µm): 655.0 Median (µm): 325.3 Median (µm): 709.8 Mean value (µm): Medium sand (326.8) Mean value (µm): Coarse sand (700.8) Sorting: Moderately well * The sample is not uni-modal. For this reason, sorted (1.46) statistical information on the sorting and skew is Skewness: Almost symmetric unreliable and therefore not listed here. (0.07) Explanations and supplementary information Distinct boundary between coarse sand (strong backscatter intensity, upper half of the image) and medium sand (lower backscatter intensity, lower half of the image). The grab samples show that the sediment types are coarse and medium sand. 62 Hydroacoustic Catalogue, Sediment types

Gravelly sand

Hydroacoustic image

Display Image size Heading Catalogue no. Mosaic 300 x 400 m N-S 8

Documentation Description of location (hydroacoustic image) Record date 14 September 2014 DK Conditions during recording Wind: NE, 6 Bft Towing speed (kn) 5 Device type (& brand) Teledyne Benthos C3D

Frequency (kHz) 200 North Sea DE Gain 7 Processing software SonarWiz

Comments: Range = 100 m NL Coordinates: N 55.00483° E 007.63074° Hydroacoustic Catalogue, Sediment types 63

Gravelly sand

Photo/video documentation

Description of the image Position of grab sample: N 55.00473° E 007.63271°

Description of the grab sample Gravelly sand Grain size distribution

Stat. parameters* 1st mode (µm): 1850.0 2nd mode (µm): 655.0 Median (µm): 1546.1 Mean value Coarse sand (µm): (1174.3)

* The sample is not uni-modal. For this reason, statistical information on the sorting and skew is unreliable and therefore not listed here.

Explanations and supplementary information The grab sample shows that the sediment type is gravelly sand according to the Folk classification system. The sonar image shows a typical backscatter pattern for sandy-gravelly sediments. Since it is easy to con- fuse the signature with that of sandy gravel, it would be impossible to clearly interpretate the sonograph and identify the sediment type without ground truthing (here: grab sample). 64 Hydroacoustic Catalogue, Sediment types

Sandy gravel

Hydroacoustic image

Display Image size Heading Catalogue no. Mosaic 300 x 400 m N-S 9

Documentation Description of location (hydroacoustic image) Record date 12 September 2014 DK Conditions during recording Wind: E, 3 Bft Towing speed (kn) 5 Device type (& brand) Teledyne Benthos C3D

Frequency (kHz) 200 North Sea DE Gain 7 Processing software SonarWiz

Comments: Range = 100 m NL Coordinates: N 54.85245° E 007.66129° Hydroacoustic Catalogue, Sediment types 65

Sandy gravel

Photo/video documentation

Description of the image Position of grab sample: N 54.852156° E 007.66357°

Description of the grab sample Sandy gravel Grain size distribution

Stat. parameters 1st mode (µm): 1850.0 Median (µm): 1890.8 Mean value (µm): Very fi ne gravel (2014.5) Sorting: Moderately sorted (1.9) Skewness: Positiv skew (0.18)

Explanations and supplementary information The grab sample shows that the sediment type is gravelly sand according to the Folk classification system. The sonar image shows a typical backscatter pattern for sandy-gravelly sediments. Since it is easy to con- fuse the signature with that of gravelly sand, it would be impossible to clearly interpretate the sonograph and identify the sediment type without ground truthing (here: grab sample). 66 Hydroacoustic Catalogue, Sediment types

Gravel/Stones

Hydroacoustic image

Display Image size Heading Catalogue no. Mosaic 1.7 x 2.5 km NE/SW 10

Documentation Description of location (hydroacoustic image) Record date 18 May 2013 DK Conditions during recording calm sea Towing speed (kn) 6.5 Device type (& brand) Edgetech-4200 MP Frequency (kHz) 300 Gain 14 North Sea DE Processing software SonarWIz Comments: Range = 230 m, Slant-range corrected, EGN NL Coordinates: N 54.69303° E 006.95756° Hydroacoustic Catalogue, Sediment types 67

Gravel/Stones

Photo/video documentation

Description of the image Position of grab sample: N 54.69075° Position of video recording: N 54.6908° E 006.96662° E 006.966°

Description of the grab sample Heterogeneous sediment structure (Fine sand, Medium sand, Gravel, Stones) Grab samples that were taken from the areas with high backscatter intensities show a heterogeneous sediment mixture of fine sands, medium sands, gravel and stones (up to 7 cm). The fraction > 2 mm was sieved out for analysis in the lab (see the grain size distribution).

Grain size distribution (Sample 46)

Stat. parameters 1st mode (µm): 173.5 Median (µm): 157.5 Mean value Fine sand (µm): (149.4) Sorting: Moderately sorted (1.97) Skewness: Very negative skew (-0.35) 68 Hydroacoustic Catalogue, Sediment types

Stone deposit I

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 150 x 300 m E 11

Documentation Description of location (hydroacoustic image) Record date 08 July 2011 DK Conditions during recording calm sea Towing speed (kn) 5 Device type (& brand) Benthos 1624 Frequency (kHz) 400 Gain 9 North Sea DE Processing software SonarWiz Comments: Range = 75 m NL Coordinates: N 54.16032° E 007.90290° Hydroacoustic Catalogue, Sediment types 69

Stone deposit I

Explanations and supplementary information Another example of stone fields (area is adjacent to the area in the previous example) 70 Hydroacoustic Catalogue, Sediment types

Stone deposit II

Hydroacoustic image

Display Image size Heading Catalogue no. Mosaic 0.9 x 0.5 km NE/SW 12

Documentation Description of location (hydroacoustic image) Record date 12–14 November 2012 DK Conditions during recording Swell 1–2 m Towing speed (kn) 5 Device type (& brand) Benthos 1624 Frequency (kHz) 100 Gain 9 North Sea DE Processing software SonarWiz Comments: Range = 150 m NL Coordinates: N 53.9270° E 006.2070° Hydroacoustic Catalogue, Sediment types 71

Stone deposit II

Photo/video documentation

Scale in figures: 13 cm between the laser points

Description of the image

Position of video recording, N 55.92310° Position of video recording, N 53.92326° left: E 006.21355° right: E 006.21290°

Explanations and supplementary information

Stone deposits in the North Sea (here in the Natura 2000 protected area “Borkum Reef Ground”) often show a relatively low number of stones. Medium to coarse sandy sediments are found between the individual stones. 72 Hydroacoustic Catalogue, Sediment types

Lag sediment

Hydroacoustic image

Display Image size Heading Catalogue no. Mosaic 80 x 50 m W 13

Documentation Description of location (hydroacoustic image) DK Baltic Sea Record date 13 April 1999 Conditions during recording Towing speed (kn) 3.3 Device type (& brand) EG&G DF-1000 Frequency (kHz) 100 & 384 Gain Processing software Own software (IOW/F. Tauber) DE Comments: Range = 102 m Coordinates: N 54.196° E 011.603°

74 Hydroacoustic Catalogue, Sediment types

Peat

Hydroacoustic image

Display Image size Heading Catalogue no. Mosaic 170 x 150 m W 14

Documentation Description of location (hydroacoustic image) DK Baltic Sea Record date 25 June 2012 Conditions during recording Towing speed (kn) 3.9 Device type (& brand) EG&G DF-1000 Frequency (kHz) 100 & 384 Gain Processing software Own software (IOW/F. Tauber) DE Comments: Range = 84 m Coordinates: N 54.612° E 013.400° Hydroacoustic Catalogue, Sediment types 75

Peat

Photo/video documentation

Outcrop of peat

Description of the image Position of video recording: N 54.612° E 013.400°

Explanations and supplementary information Hydroacoustic image: Green arrows mark the outcrop of the layer of peat (light area).

Photo: A layer of peat about 50 cm high with mussels and algae growth; in front: sand with algae. 76 Hydroacoustic Catalogue, Sediment types

Comparison: Gravel/Shells/Medium sand

Hydroacoustic image

Display Image size Heading Catalogue no. Mosaic 5.4 x 9.5 km NE/SW 15

Documentation Description of location (hydroacoustic image) Record date 18 May 2013 DK Conditions during recording calm sea Towing speed (kn) 6.5 Device type (& brand) Edgetech-4200 MP Frequency (kHz) 300 Gain 14 North Sea DE Processing software SonarWIZ Comments: Range = 230 m, Slant-range corrected NL Coordinates: N 54.77956° E 007.15151° Hydroacoustic Catalogue, Sediment types 77

Comparison: Gravel/Shells/Medium sand

Photo/video documentation

Position 82

Description of the image Position of grab sample: N 54.79038° E 007.20868°

Description of the grab sample Fine gravelly medium sand Grain size distribution (Sample 82)

Stat. parameters 1st mode (µm): 347.0 Median (µm): 301.8 Mean value Medium sand (µm): (278.4) Sorting: Poorly sorted (2.07) Skewness: Very negative skew (-0.50) 78 Hydroacoustic Catalogue, Sediment types

Comparison: Gravel/Shells/Medium sand

Photo/video documentation

Position 68

Description of the image Position of grab sample N 54.76382° E 007.5137°

Description of the grab sample Medium sand Grain size distribution (Sample 68)

Stat. parameters 1st mode (µm): 263.0 Median (µm): 262.7 Mean value Medium sand (µm): (264.5) Sorting: Well sorted (1.41) Skewness: Almost symmetric (-0.03) Hydroacoustic Catalogue, Sediment types 79

Comparison: Gravel/Shells/Medium sand

Photo/video documentation

Position 66 Description of the image Position of video recording: N 54.7823° E 007.1406°

Description of the grab sample Shell debris 80 Hydroacoustic Catalogue, Bedrock

3 Bedrock

Rocky substrate

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 150 x 300 m E 16

Documentation Description of location (hydroacoustic image) Record date 08 July 2011 DK Conditions during recording calm sea Towing speed (kn) 5 Device type (& brand) Benthos 1624 Frequency (kHz) 400 Gain 9 North Sea DE Processing software SonarWiz Comments: Range = 75 m NL Coordinates: N 54.16276° E 007.90835° Hydroacoustic Catalogue, Bedrock 81

Rocky substrate

Explanations and supplementary information Another example of a rocky substrate (area is adjacent to the area in the previous example) 82 Hydroacoustic Catalogue, Seabed features – Dynamic sediment structures

4 Seabed features – Dynamic sediment structures

Dunes I

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 300 x 275 m SE 17

Documentation Description of location (hydroacoustic image) Record date 31 May 2012 DK Conditions during calm sea recording Towing speed (kn) 5 Device type (& brand) Benthos 1624

Frequency (kHz) 100 & 400 North Sea DE Gain 9 Processing software SonarWiz

Comments: Range = 150 m NL Coordinates: N 53.55018° E 008.18687° Hydroacoustic Catalogue, Seabed features – Dynamic sediment structures 83

Dunes I

Description of the sample Medium sand Position of grab sample: N 53.5518° E 008.1849° Grain size distribution

Stat. parameters 1st mode (µm): 387.0 Median (µm): 416.8 Mean value (µm): Medium sand (414.3) Sorting: Moderately well sorted (1.56) Skewness: Negative skew (-0.14)

Explanations and supplementary information Another example of dunes: Documentation Description of Coordinates: (hydroacoustic image) location N 53.67138° E 008.08752° Record date 14.05.2012 Conditions during calm sea recording Towing speed (kn) 5 Device type (& brand) Benthos 1624 Frequency (kHz) 400 Gain 9 Processing software SonarWiz Comments: Range = 150 m 84 Hydroacoustic Catalogue, Seabed features – Dynamic sediment structures

Dunes II

Hydroacoustic image

Display Image size Heading Catalogue no. Mosaic 3.3 x 5 km NE/SW 18

Documentation Description of location (hydroacoustic image) Record date 01 May 2013 DK Conditions during calm sea recording Towing speed (kn) 6.5 Device type (& brand) EdgeTech-4200 MP

Frequency (kHz) 300 North Sea DE Gain 14 Processing software SonarWiz

Comments: Range = 230 m NL Slant-range corrected, EGN Coordinates: N 54.609° E 006.051° Hydroacoustic Catalogue, Seabed features – Dynamic sediment structures 85

Dunes II

Explanations and supplementary information Sediment type: Fine sand Profile length: 2 km Height of bedforms: ~1.2 m Length of bedforms: 200–400 m 86 Hydroacoustic Catalogue, Seabed features – Dynamic sediment structures

Ripple structures

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall (excerpt) 73 (wide) x 80 (high) m SW 19

Documentation Description of location (hydroacoustic image) DK Baltic Sea Record date 21 October 2007 Conditions during recording Towing speed (kn) 4.5 Device type (& brand) unknown Frequency (kHz) 300 und 600 Gain

Processing software Own software DE (IOW/F. Tauber) Comments: Range = 73 m Coordinates: N 54.303° E 012.119° Hydroacoustic Catalogue, Seabed features – Dynamic sediment structures 87

Ripple structures

Photo/video documentation

Measurement of the ripple wavelength Sediment sampling

Description of the image Position of grab sample: N 54.746° E 014.159°

Description of the sample Sediment analysis on board: Coarse sand/Fine gravel Sediment after granulometry: Coarse sand, poorly sorted Grain size distribution (coarsest fraction: > 2 mm, the upper limit of 8 mm is an assumption)

Stat. parameters* 1st mode (µm): 403 2nd mode (µm): 5000 Median (µm): 1043 Mean value Coarse sand (µm): (1133)

* The sample is not uni-modal. For this reason, statistical information on the sorting and skew is unreliable and therefore not listed here.

Explanations and supplementary information Explanations of the hydroacoustic images: Ripple wavelength in the middle of the hydroacoustic image recorded is about 0.7 m 88 Hydroacoustic Catalogue, Seabed features – Dynamic sediment structures

Ripple structures

Another example of ripple structures:

Documentation Display Mosaic (hydroacoustic image) Image size a) 260 x 150 m Record date a) 31 March 2013 b) 290 x 150 m b) 29 March 2013 Heading S Towing speed (kn) 4.5 Description of Coordinates: Device type (& brand) X-Star location a) N 54.962° E 006.849° Processing software SonarWiz b) N 54.671° Comments: Range = 78 m E 007.349°

a) Coarse sediment b) Fine sediment

90 Hydroacoustic Catalogue, Seabed features – Dynamic sediment structures

“Transport bodies”

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 300 x 165 m N 20

Documentation Description of location (hydroacoustic image) Record date 14 October 2011 DK Conditions during Swell 1 m recording Towing speed (kn) 5 Device type (& brand) Benthos 1624

Frequency (kHz) 100 & 400 North Sea DE Gain 9 Processing software SonarWiz

Comments: Range = 150 m NL Coordinates: N 54.15462° E 007.97279° Hydroacoustic Catalogue, Seabed features – Dynamic sediment structures 91

“Transport bodies”

Photo/video documentation

Description of the image Position of grab sample: N 54.1569° E 007.9848°

Description of the sample Mittel- bis Coarse sand Grain size distribution (lower limit open in the original data)

Stat. parameters 1st mode (µm): 547.5 2nd mode (µm): 230.0 Median (µm): 555.2 Mean value Medium sand (µm): (398.4)

* The sample is not uni-modal. For this reason, statistical information on the sorting and skew is unreliable and therefore not listed here. 92 Hydroacoustic Catalogue, Seabed features – Dynamic sediment structures

“Transport bodies”

Explanations and supplementary information Another example of Transport bodies: Documentation Display Mosaic (hydroacoustic image) Image size 1.15 x 2.1 km Record date 03–04 October 2012 Heading N/S Conditions during Swell 1 m Description of Coordinates: recording location N 54.157° Towing speed (kn) 5 E 008.001° Device type (& brand) YellowFin Frequency 330 Gain 50% Processing software SonarWiz Comments: Range = 125 m

94 Hydroacoustic Catalogue, Seabed features – Dynamic sediment structures

Small-scale facies change

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 550 x 160 m SW 21

Documentation Description of location (hydroacoustic image) Record date 04 May 2013 DK Conditions during calm sea recording Towing speed (kn) 6.5 Device type (& brand) EdgeTech-4200 MP

Frequency (kHz) 300 North Sea DE Gain 14 Processing software EdgeTech Discover 4200-MP NL Comments: Range = 230 m Coordinates: N 54.686° E 006.963° Hydroacoustic Catalogue, Seabed features – Dynamic sediment structures 95

Small-scale facies change

Explanations and supplementary information

Corresponding excerpt of mosaic (image size 500 x 500 m) 96 Hydroacoustic Catalogue, Biogenic structures

5 Biogenic structures

Sead mussel area (with marks from fishing)

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 150 x 225 m W 22

Documentation Description of location (hydroacoustic image) Record date 02 December 2009 DK Conditions during calm sea recording Towing speed (kn) 5 Device type (& brand) Benthos 1624

Frequency (kHz) 400 North Sea DE Gain 9 Processing software SonarWiz

Comments: Range = 75 m NL Coordinates: N 53.61416° E 008.19496° Hydroacoustic Catalogue, Biogenic structures 97

Sead mussel area (with marks from fishing)

Photo/video documentation

a) b)

Description of the image Position of grab sample a): N 53.61518° b): N 53.61219° E 008.19610° E 008.19517°

Description of the sample a) Mussels on muddy sand b) Muddy sand Grain size distribution (lower limit open in the original data)

a) Stat. parameters b) Stat. parameters* 1st mode (µm): 163.0 1st mode (µm): 163.0 Median (µm): 164.1 2nd mode (µm): 0.650 Mean value (µm): Fine sand (164.2) Median (µm): 138.7 Sorting: Poorly sorted (2.11) Mean value (µm): Coarse silt (29.6) Skewness: Negative skew (-0.29) * The sample is not uni-modal. For this reason, statistical information on the sorting and skew is unreliable and therefore not listed here. 98 Hydroacoustic Catalogue, Biogenic structures

Sead mussel area (with marks from fishing)

Explanations and supplementary information Hydroacoustic image: Dark grey structures = mussels on muddy sand Light grey structures = muddy sand (without mussels)

Mussel dredges

Source: Niedersächsische Muschelfischer GbR

Mussel dredge

Source: Niedersächsische Muschelfischer GbR

100 Hydroacoustic Catalogue, Biogenic structures

Sead mussel area (with spilling marks)

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 150 x 150 m W 23

Documentation Description of location (hydroacoustic image) Record date 02 December 2009 DK Conditions during calm sea recording Towing speed (kn) 5 Device type (& brand) Benthos 1624

Frequency (kHz) 400 North Sea DE Gain 9 Processing software SonarWiz

Comments: Range = 75 m NL Coordinates: N 53.61282 E 007.18825 Hydroacoustic Catalogue, Biogenic structures 101

Sead mussel area (with spilling marks)

Photo/video documentation

a) b)

Description of the image Position of grab sample a): N 53.61518° b): N 53.61219° E 008.19610° E 008.19517°

Description of the sample a) Mussels on muddy sand b) Muddy sand Grain size distribution :

Explanations and supplementary information Hydroacoustic image: Dark, linear structures = seeded mussels

Diagram: Sowing mussels

1 – Loading space 2 – Pump 3 – Mussel culture

Source: Niedersächsische Muschelfischer GbR

104 Hydroacoustic Catalogue, Biogenic structures

Sand in combination with lanice conchilega

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 400 x 290 m N 24

Documentation Description of location (hydroacoustic image) Record date 06 June 2013 DK Conditions during Swell 0.5 m recording Towing speed (kn) 5 Device type (& brand) Benthos 1624

Frequency (kHz) 100 North Sea DE Gain TVG (4.7/ +0.08/ +1) Processing software Triton Isis

Comments: Range = 100m NL Coordinates: N 54.981° E 007.769° Hydroacoustic Catalogue, Biogenic structures 105

Sand in combination with lanice conchilega

Explanations and supplementary information

Lanice conchilega in a layer of homogeneous fine sand. The squares are 10 x 10 cm in size. The average colonization density is 7 lanice organisms per square decimetre. 106 Hydroacoustic Catalogue, Anthropogenic structures

6 Anthropogenic structures

Wreck

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 220 x 55 m SW 25

Documentation Description of location (hydroacoustic image) Record date 05 May 2013 DK Conditions during calm sea recording Towing speed (kn) 6.6 Device type (& brand) Edgetech-4200MP

Frequency (kHz) 300 North Sea DE Gain 14 Processing software EdgeTech Discover 4200-MP NL Comments: Range = 230 m Coordinates: N 54.781° E 007.092° Hydroacoustic Catalogue, Anthropogenic structures 107

Wreck

Explanations and supplementary information Another example of wrecks:

Display Waterfall Documentation (hydroacoustic image) Image size 80 x 170 m Record date 02 May 2013 Heading SW Conditions during small waves Description of Coordinates: recording location N 54.639° E 007.041° Towing speed (kn) 6.9 Device type (& brand) Edgetech-4200MP Frequency (kHz) 300 Gain 14 Processing software EdgeTech Discover Comments: Range = 230 m, Slant-range corrected EGN

The clearly visible acoustic shadow can be seen to the left of the wreck. 108 Hydroacoustic Catalogue, Anthropogenic structures

Wreck

Explanations and supplementary information Another example of wrecks:

Documentation Display Waterfall (hydroacoustic image) Image size 300 x 225 m Record date 13 October 2011 Heading N Conditions during Swell 1 m Description of Coordinates: recording location N 54.16398° Towing speed (kn) 5 E 007.96239° Device type (& brand) Benthos 1624 Frequency (kHz) 100 Gain 9 Processing software SonarWiz Comments: Range = 150 m

Hydroacoustic Catalogue, Anthropogenic structures 109

Wreck

Explanations and supplementary information Another example of wrecks:

Documentation Display Waterfall (hydroacoustic image) Image size 120 x 40 m Record date 21 May 2013 Heading NE Conditions during Swell 1 m Description of Coordinates: recording location N 54.899° Towing speed (kn) 4.5 E 006.424° Device type (& brand) YellowFin Frequency (kHz) 330 Gain 50 % Processing software SonarWiz Comments: Range = 125 m

Remains of a wreck that are buried in sand for the most part. 110 Hydroacoustic Catalogue, Anthropogenic structures

Dredging marks

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 300 x 225 m S 26

Documentation Description of location (hydroacoustic image) Record date 31 May 2012 DK Conditions during calm sea recording Towing speed (kn) 5 Device type (& brand) Benthos 1624

Frequency (kHz) 100 North Sea DE Gain 9 Processing software SonarWiz

Comments: Range = 150 m NL Coordinates: N 53.52203° E 008.17820° Hydroacoustic Catalogue, Anthropogenic structures 111

Dredging marks

Explanations and supplementary information Another example of dredging marks

Hopper dredger

Source: WSV.de

Source: Schleswig-Holstein Agency for Coastal Defence, National Park and Marine Conservation (LKN-SH) 112 Hydroacoustic Catalogue, Anthropogenic structures

Otter board marks

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 160 x 340 m W 27

Documentation Description of location (hydroacoustic image) DK Baltic Sea Record date 13 October 2006 Conditions during recording Towing speed (kn) 8.9 Device type (& brand) EG&G DF-1000 Frequency (kHz) 100 Gain

Processing software Own software DE (IOW/F. Tauber) Comments: Range = 80 m Coordinates: N 54.488° E 010.389° Hydroacoustic Catalogue, Anthropogenic structures 113

Otter board marks

Explanations and supplementary information Explanations of the hydroacoustic image:

Thin, dark lines (can be best seen in the left half of the image) are marks left behind by otter boards. In places, these lines consist of a series of points that are created when otter boards repeatedly touch the seabed before they lift and lower again. Dark spots in the middle of the image and on the right half of the image are created by the propeller wash of the ship and air bubbles in the water.

Otter boards Otter boards are used in trawl fishing to keep the fishing net open. They dig into the seabed and leave deep grooves behind. The grooves are filled up again with fine sediment over time. Trawling net with otter boards

1 Cod line 2 Cod end 3 Legs 4 Ground rope with sinkers 5 Headline with floats 6 Otter boards 7 Towing warps 8 Outriggers 9 Bridles

Source: TAIT, R. V. (1981): Meeresökologie. Das Meer als Umwelt. (Marine Ecology. The Sea as an Environ- ment.) Georg Thieme Verlag, Stuttgart, 305 pp.

Diagram of a bottom trawl net with otter boards (from: Werner, F.; Hoffmann, G.; Bernhard, M.; Milkert, D.; Vikgren, K. 1990: Sedimentologische Auswirkungen der Grundfischerei in der Kieler Bucht (westliche Ostsee) (Sedimentological effects of bottom fishing in the Bay of Kiel (western Baltic Sea)). Meyniana, 42, 123–151) 114 Hydroacoustic Catalogue, Anthropogenic structures

Otter board marks

Explanations and supplementary information Another example of otter board marks:

Documentation Display Waterfall (hydroacoustic image) Description of Coordinates: Record date 31 May 2012 location N 53.497° E 008.184° Conditions during calm sea recording Towing speed (kn) 5 Device type (& brand) Benthos 1624 Frequency (kHz) 400 Gain 9 Processing software SonarWiz Comments: Range = 150 m Hydroacoustic Catalogue, Anthropogenic structures 115

Otter board marks

Explanations and supplementary information Another example of otter board marks:

Documentation Display Waterfall (hydroacoustic image) Description of Coordinates: Record date 09 November 2011 location N 53.66589° E 008.06887° Conditions during calm sea recording Towing speed (kn) 5 Device type (& brand) Benthos 1624 Frequency (kHz) 100 Gain 9 Processing software SonarWiz Comments: Range = 150 m 116 Hydroacoustic Catalogue, Anthropogenic structures

Beam trawls

Hydroacoustic image

Display Image size Heading Catalogue no. Mosaic 4.3 x 2.3 km NE/SW 28

Documentation Description of location (hydroacoustic image) Record date 09–10 May 2013 DK Conditions during calm sea recording Towing speed (kn) 6.5 Device type (& brand) Edgetech-4200MP

Frequency (kHz) 300 North Sea DE Gain 14 Processing software SonarWiz

Comments: Range = 150 m, NL Slant-range corrected, EGN Coordinates: N 54.887° E 006.958° Hydroacoustic Catalogue, Anthropogenic structures 117

Anchor chain marks

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 160 x 160 m SW 29

Documentation Description of location (hydroacoustic image) DK Baltic Sea Record date 11 March 2005 Conditions during recording Towing speed (kn) 4.2 Device type (& brand) EG&G DF-1000 Frequency (kHz) 100 Gain

Processing software Own software DE (IOW/F. Tauber) Comments: Range = 80 m Coordinates: N 54.062° E 010.812°

Explanations and supplementary information Fan/like anchor chain marks caused by the swaying of the ship. 118 Hydroacoustic Catalogue, Anthropogenic structures

Transit pipeline

Hydroacoustic image

Display Image size Heading Catalogue no. Mosaic 6.6 x 3.7 km NE/SW 30

Documentation Description of location (hydroacoustic image) Record date 10–12 May 2013 DK Conditions during calm sea recording Towing speed (kn) 6.5 Device type (& brand) Edgetech-4200MP

Frequency (kHz) 300 North Sea DE Gain 14 Processing software SonarWiz

Comments: Range = 230 m, NL Slant-range corrected, EGN Coordinates: N 54.893° E 006.8502° Hydroacoustic Catalogue, Anthropogenic structures 119

Transit pipeline

Explanations and supplementary information

Transit pipeline (Source: BSH)

Laying a transit pipeline (source: BSH) 120 Hydroacoustic Catalogue, Anthropogenic structures

Anchorage

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 390 x 105 m SW 31

Documentation Description of location (hydroacoustic image) Record date 06 May 2013 DK Conditions during calm sea recording Towing speed (kn) 6.4 Device type (& brand) EdgeTech- 4200MP

Frequency (kHz) 300 North Sea DE Gain 14 Processing software EdgeTech Discover 4200-MP NL Comments: Range = 230 m, Slant-range corrected, EGN Coordinates: N 54.684° E 006.783° Hydroacoustic Catalogue, Anthropogenic structures 121

Anchorage

Explanations and supplementary information The dark line leading away from the point of anchorage shows the chain that is fastened to the buoy.

Anchorage

Chain

Corresponding excerpt of mosaic (image size 800 x 800 m) 122 Hydroacoustic Catalogue, Anthropogenic structures

Anchorage

Explanations and supplementary information

Another example of anchorage

Documentation Display Waterfall (hydroacoustic image) Image size 190 x 190 m Record date 25 October 1999 Heading O Towing speed (kn) 4.9 Description of Coordinates: Device type (& brand) EG&G DF-1000 location N 54.062° Frequency (kHz) 384 E 011.455° Processing software Own software (IOW/F. Tauber) Comments: Range = 78 m

Scouring

Buoy with anchor

124 Hydroacoustic Catalogue, Anthropogenic structures

Sand dredging

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall Width: 250 m 32

Documentation Description of location (hydroacoustic image) Record date 24 August 2007 DK Conditions during recording Towing speed (kn) 7.4 Device type (& brand) YellowFin

Frequency (kHz) 330 North Sea DE Gain Processing software YellowFin

Comments: Range = 125 m, NL Slant-range corrected, EGN Coordinates: N 54.913° E 008.188° Hydroacoustic Catalogue, Anthropogenic structures 125

Sand dredging

Explanations and supplementary information Another example of sand dredging (area is adjacent to the area in the previous example) (Changes in comparison to the previous example: towing speed: 6.4 kn)

Image width: 250 m 126 Hydroacoustic Catalogue, Anthropogenic structures

Dumped dredge spoil

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 160 x 180 m N 33

Documentation Description of location (hydroacoustic image) DK Baltic Sea Record date 12 October 1995 Conditions during recording Towing speed (kn) 4.6 Device type (& brand) EG&G DF-1000 Frequency (kHz) 100 Gain

Processing software Own software DE (IOW/F. Tauber) Comments: Range = 80 m Coordinates: N 54.287° E 012.109°

Explanations and supplementary information Boulder clay (dark) dumped on sand (light). The boulder clay in this recording derived from the deepening of the sea channel in Rostock. Hydroacoustic Catalogue, Anthropogenic structures 127

Foundation of a platform

Hydroacoustic image

Display Image size Heading Catalogue no. Mosaic 230 x 210 m NE 34

Documentation Description of location (hydroacoustic image) Record date 03 May 2013 DK Conditions during calm sea recording Towing speed (kn) 6.6 Device type (& brand) EdgeTech- 4200MP

Frequency (kHz) 300 North Sea DE Gain 14 Processing software EdgeTech Discover 4200-MP NL Comments: Range = 230 m, Coordinates: N 54.701° Slant-range corrected EGN E 007.167°

Explanations and supplementary information Foundation of the former research platform NORDSEE. The acoustic shadow of the object can clearly be seen in the southeast direction. 128 Hydroacoustic Catalogue, Artefacts in the water column

7 Artefacts in the water column

Propeller noise

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 300 x 375 m SE 35

Documentation Description of location (hydroacoustic image) Record date 15 May 2012 DK Conditions during calm sea recording Towing speed (kn) 5 Device type (& brand) Benthos 1624

Frequency (kHz) 100 North Sea DE Gain 9 Processing software SonarWiz

Comments: Range = 150 m NL Coordinates: N 53.51940° E 008.17056° Hydroacoustic Catalogue, Artefacts in the water column 129

Propeller noise

Explanations and supplementary information A vessel passes the survey vessel and then crosses its course. The propeller wash of the passing ship is clearly visible on the sonograph. The air bubbles appearing in the propeller wash have a reflection coeffici- ent of -1 compared to that of the water column. The entire acoustic energy is reflected by the air bubbles. 130 Hydroacoustic Catalogue, Artefacts in the water column

Schools of fish

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 160 x 170 m SW 36

Documentation Description of location (hydroacoustic image) DK Baltic Sea Record date 11 March 2005 Conditions during recording Towing speed (kn) 4.6 Device type (& brand) EG&G DF-1000 Frequency (kHz) 384 Gain

Processing software Own software DE (IOW/F. Tauber) Comments: Range = 80 m Coordinates: N 54.054° E 010.792°

Explanations and supplementary information The air-filled swim bladders of a school of fish generate acoustic echoes that look like clouds of dark points (green arrows). Hydroacoustic Catalogue, Artefacts in the water column 131

Air bubbles

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 160 x 170 m ONO 37

Documentation Description of location (hydroacoustic image) DK Baltic Sea Record date 11 October 2006 Conditions during recording Towing speed (kn) 4.6 Device type (& brand) EG&G DF-1000 Frequency (kHz) 384 Gain

Processing software Own software DE (IOW/F. Tauber) Comments: Range = 80 m Coordinates: N 54.112° E 010.986°

Explanations and supplementary information Air bubbles in the water appear as dark points and clouds (green arrows). The elongated aggregations of such points are created by strong swell and breaking waves. 132 Hydroacoustic Catalogue, Artefacts in the water column

Pycnocline

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 160 x 190 m NNO 38

Documentation Description of location (hydroacoustic image) DK Baltic Sea Record date 06 May 2006 Conditions during recording Towing speed (kn) 4.9 Device type (& brand) EG&G DF-1000 Frequency (kHz) 100& 384 Gain

Processing software Own software DE (IOW/F. Tauber) Comments: Range = 80 m Coordinates: N 54.389° E 012.394° Hydroacoustic Catalogue, Artefacts in the water column 133

Thermocline

Explanations and supplementary information A pycnocline (thermocline or halocline) induces internal waves by which streaks or wave patterns are created in the image (green arrows) that often exhibit a dark side and a light side. Since the seafloor is fuzzier in the recorded image, structures cannot be recognised, especially near the edges.

Another example

Documentation Display Waterfall (hydroacoustic image) Image size 160 x 190 m Record date 23 May 2007 Heading NO Towing speed (kn) 4.9 Description of Coordinates: Device type (& brand) EG&G DF-1000 location N 54.475° E 012.723° Frequency (kHz) 100 & 384 Processing software Own software (IOW/F. Tauber) Comments: Range = 80 m

134 Hydroacoustic Catalogue, Artefacts in the water column

Suspended matter in the water

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 160 x 140 m E 39

Documentation Description of location (hydroacoustic image) DK Baltic Sea Record date 4 November 2006 Conditions during Wind 9 to 11 m/s recording from the West, strong turbidity and flakes in the water Towing speed (kn) 5 Device type (& brand) EG&G DF-1000 Frequency (kHz) 100 Gain DE Software Own software (IOW/F. Tauber) Coordinates: N 54.479° E 012.826° Comments: Range = 75 m Hydroacoustic Catalogue, Artefacts in the water column 135

Explanations and supplementary information Suspended particulate matter appears as fuzzy dark clouds in side-scan sonar images. While recording this specificside-scan sonar images, there were strong, gusty winds of speeds from 9 to 11 m/s from the west. The water depth was about 8 m. While recording a video profile on the same day, the water close to the seafloor was completely cloudy due to suspended matter and flakes. The waves were clearly noticeable even when the ROV camera was close to the seafloor. The visibility of the camera was 0 to 0.5 m. Temporarily, it was completely dark due to the cloudiness.

ROV still camera shot with suspended matter (cloudy water) and flocs (dark) in the water column. The grab sampler of the ROV is on the right. The bright spots on the seafloor are mussel shells. (Note: the clock on the camera was 2 days behind. The recording was taken on 4 November 2006 about 4 hours before the side-scan recording was taken in the same area.) 136 Hydroacoustic Catalogue, Interferences during data recording

8 Interferences during data recording

Acoustic interference

Hydroacoustic image

Display Image size Heading Catalogue no. Mosaic 160 x 160 m S 40

Documentation Description of location (hydroacoustic image) Record date 04 October 2012 DK Conditions during recording Towing speed (kn) 4 Device type (& brand) YellowFin

Frequency (kHz) 330 North Sea DE Gain 70 % Processing software SonarWiz

Comments: Range = 125 m, NL Slant-range corrected EGN Coordinates: N 54.513° E 007.989° Hydroacoustic Catalogue, Interferences during data recording 137

Acoustic interference

Explanation for the interference The interferences (black lines) are created due to the simultaneous application of other acoustic instruments with similar frequencies.

“Trouble Shooting” The interfering noise can be eliminated by triggering the instruments at different times. 138 Hydroacoustic Catalogue, Interferences during data recording

Acoustic interference by SES sub-bottom profilers

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 300 x 300 m SW 41

Documentation Description of location (hydroacoustic image) Record date 13 Feb. 2013 DK Conditions during Swell 1 m recording Towing speed (kn) 5 Device type (& brand) Benthos 1624

Frequency (kHz) 100 North Sea DE Gain 9 Processing software SonarWiz

Comments: Range = 150 m, NL Slant-range corrected Coordinates: N 53.99598° E 006.28210° Hydroacoustic Catalogue, Interferences during data recording 139

Acoustic interference by SES sub-bottom profilers

Explanation for the interference A pattern of black dashes can be seen on both channels of the side-scan sonar image. The interference is caused by the simultaneous operation of another acoustic source (in this case: SES sediment echo sounder).

“Trouble Shooting” Synchronise the triggering sequence of the two devices. If necessary, the measurements have to be done at different times (1 with side-scan sonar, 1 with a sediment echo sounder). 140 Hydroacoustic Catalogue, Interferences during data recording

Acoustic interference due to machine noise

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 300 x 337 m S 42

Documentation Description of location (hydroacoustic image) Record date 31 May 2012 DK Conditions during calm sea recording Towing speed (kn) 5 Device type (& brand) Benthos 1624

Frequency (kHz) 100 North Sea DE Gain 9 Processing software SonarWiz

Comments: Range = 150 m NL Coordinates: N 53.47913° E 008.20372° Hydroacoustic Catalogue, Interferences during data recording 141

Acoustic interference due to machine noise

Explanation for the interference Black, caused by the machines of the ship, can be seen on the left channel of the side-scan sonar image.

“Trouble Shooting” Change the speed of the machine and tow the towfish at a greater distance from the vessel. 142 Hydroacoustic Catalogue, Interferences during data recording

Acoustic interference – Reflection of the water column

Hydroacoustic image

Reflection of the water surface

Nadir

Slant-range corrected

Display Image size Heading Catalogue no. Mosaic 150 x 250 m N 43

Documentation Description of location (hydroacoustic image) Record date 30 September 2012 DK Conditions during recording Towing speed (kn) 5 Device type (& brand) YellowFin

Frequency (kHz) 330 North Sea DE Gain 70% Processing software YellowFin

Comments: Range = 125 m, NL Slant-range corrected EGN Coordinates: N 54.433° E 008.037° Hydroacoustic Catalogue, Interferences during data recording 143

Acoustic interference – Reflection of the water column

Explanation for the interference Another example of a reflection of the water column:

This example is adjacent to the previous example.

Reflection of the water surface Water column Water

Signal from seabed

Multiple of the signal from seabed

When the side-scan sonar unit is towed too close to the seafloor, then the signal from the seabed arrives before the signal from the surface of the water and is therewith displayed first. This can lead to misinter- pretations.

“Trouble Shooting” In this case, the side-scan sonar unit must be towed at a greater distance to the seafloor. 144 Hydroacoustic Catalogue, Interferences during data recording

Quenching

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall Width = 250 m 44

Documentation Description of location (hydroacoustic image) Record date 28 August 2007 DK Conditions during recording Towing speed (kn) 7.7 Device type (& brand) YellowFin

Frequency (kHz) 330 North Sea DE Gain Processing software

Comments: Range = 125 m NL Coordinates: N 55.171° E 008.148° Hydroacoustic Catalogue, Interferences during data recording 145

Quenching

Explanation for the interference Quenching arises when numerous air bubbles in the water are situated close to the sounder of the side- scan sonar unit and the acoustic signal is absorbed and reflected by the bubbles. This effect can arise when there is a strong swell with breaking waves or when the side-scan sonar towfish is led too close to the surface of the water.

“Trouble Shooting” If necessary, hang the device lower. 146 Hydroacoustic Catalogue, Interferences during data recording

Swell

Hydroacoustic image

Display Image size Heading Catalogue no. Waterfall 400 x 337 m NW 45

Documentation Description of location (hydroacoustic image) Record date 08 November 2011 DK Conditions during Swell 2 m recording Towing speed (kn) 5 Device type (& brand) Benthos 1624

Frequency (kHz) 100 North Sea DE Gain 9 Processing software SonarWiz

Comments: Range = 200 m NL Coordinates: N 54.50018° E 006.13126° Hydroacoustic Catalogue, Interferences during data recording 147

Swell

Explanation for the interference Another example of a recording taken during rough swell

Difference in contrast to the previous example: Coordinates N 54.463° E 006.177°

The interference induced by the swell primarily consists of heave and pitch motions.

“Trouble Shooting” If the towing cable hangs steeply in the water, the motions of the ship are transferred more strongly to the towfish than in the case of a flatter angle of the towing cable. The only way to reduce the interference is to tow the towfish at a much greater depth. Shall the recorded data show no improvement, the measurements should be stopped.