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  • IWT SBO PROJECT 120003 “SEARCH”

    Archaeological heritage in the North Sea Development of an efficient assessment methodology and approach towards a sustainable

    management policy and legal framework in Belgium.

    Archeologisch erfgoed in de Noordzee Ontwikkeling van een efficiënte evaluatiemethodologie en voorstellen tot een duurzaam

    beheer in België.

    ACOUSTIC SURVEY TECHNIQUES FOR MARINE ARCHAEOLOGICAL

    INVESTIGATIONS

    WP 1.1.2

    Responsible partners: UG-RCMG, Deltares

    Authors: O. Zurita Hurtado, T. Missiaen, P. Kruiver

    June 2013

  • IWT SBO 120003 “SEARCH” WP1.1.2 ACOUSTIC SURVEY TECHNIQUES

    2

    Table of contents

    1 Introduction .................................................................................................................................... 3

    2 Principles of wave propagation and classification .......................................................................... 3

    2.1 Sound wave basics and properties .......................................................................................... 4

    2.2 Sound Wave Classification ....................................................................................................... 4

    2.3 Sound Wave Propagation Properties ....................................................................................... 5

    3 Seabed mapping .............................................................................................................................. 6

    3.1 Introduction ............................................................................................................................. 6

    3.2 Seabed mapping methods ....................................................................................................... 7

    3.2.1 Single Beam Echosounder (SBES) ..................................................................................... 7

    3.2.2 Multibeam Echosounder (MBES) ........................................................................................... 8

    3.2.3 Side Scan Sonar (SSS) ........................................................................................................... 11

    3.3 Advantages and Limitations of seabed mapping techniques ................................................ 13

    3.4 Recommendations on seabed mapping techniques .............................................................. 13

    4 Single Channel high-resolution sub-bottom profiling ................................................................... 14

    4.1 Introduction ........................................................................................................................... 14

    4.2 Sub-bottom profilers systems ................................................................................................ 15

    4.2.1 Sparker ........................................................................................................................... 16

    4.2.2 Boomer ........................................................................................................................... 17

    4.2.3 Chirp ............................................................................................................................... 19

    4.2.4 Parametric Echosounder ................................................................................................ 21

    4.3 Recommendations on single channel high-resolution sub-bottom profiling ........................ 23

    5 Multichannel high-resolution sub-bottom profiling ..................................................................... 23

    5.1 Method of multichannel seismic reflection ........................................................................... 23

    5.2 Advantages and limitations of multichannel techniques ...................................................... 25

    5.3 Recommendations for multichannel seismic reflection ........................................................ 26

    6 3D High-Resolution Seismic Reflection ......................................................................................... 26

    6.1 Method of 3D High-resolution seismic .................................................................................. 26

    6.2 Advantages and limitations of 3D high-resolution seismics .................................................. 29

    6.3 Recommendations for 3D High resolution seismics .............................................................. 30

    7 Summary of available techniques ................................................................................................. 30

    7.1 Existing acoustic techniques .................................................................................................. 30

    7.2 Acoustic techniques available at project partners ................................................................. 30

    8 Conclusions and recommendations .............................................................................................. 32

    9 References ..................................................................................................................................... 32

  • IWT SBO 120003 “SEARCH” WP1.1.2 ACOUSTIC SURVEY TECHNIQUES

    3

    1 Introduction

    Marine acoustic methods are the most widely used surveying technique to study the

    structure and properties of the seafloor and its underlying substrate. The range of available

    techniques is extensive and their capabilities have no parallel with any other non-invasive

    investigation technology. They are based on the study of the propagation characteristics of

    acoustic waves in the propagating media. The basic technique of acoustic methods consists

    of artificially generating acoustic waves and measuring the time required for the waves to

    travel from the source to an acoustic receiver. From the knowledge of the travel time and

    the propagation velocity it is possible to reconstruct the paths of the acoustic waves and

    hence to deduce information of the structure of the propagating media.

    Acoustic methods are widely used for oil and gas exploration [Telford et al., 1990] but also in

    near-surface or shallow applications like engineering, environmental studies, mineral

    exploration and archaeological investigations (e.g. Dix 2008). In marine archaeology in

    particular, penetrative and non-penetrative acoustic techniques have been successfully used

    to investigate wrecksites and buried landscapes and/or objects.

    Unfortunately, and most probably to lack of finance resources, a ‘black-box’ approach has

    often been adopted in the archaeological community with regard to penetrative techniques,

    with users accepting the resultant acoustic image as a definitive ‘snapshot’ of the sub-

    bottom substrate without understanding the physical process laying behind the technology.

    This lack of knowledge has led to an increase in expectations from users who ignore the

    limits of the techniques. Additionally, archaeologist often have to rely on data acquired for

    geo-technical purposes which often lack the high-resolution and coverage needed for

    archaeological analysis.

    It is not the intention of this report to provide a comprehensive description of all aspects

    regarding marine acoustic methods, but to provide an overview of some aspects of high

    resolution marine seismic profiling. Chapter 2 summarizes the very basics of wave

    generation, propagation and classification that are required to understand the principle of

    acoustic methods. In chapter 3, a description of bathymetry systems is given, while in

    chapter 4, conventional sub bottom profiling methods are covered, paying special attention

    to their capabilities and limitations. Chapter 5 and 6 cover latest developments in shallow

    marine investigations like multi-channel seismic reflection and 3D seismic. The last chapters

    give recommendations to accomplish the project objectives.

    2 Principles of wave propagation and classification

    This chapter is based on standard exploration seismology textbooks, e.g. [Sheriff and

    Geldart, 1995].

  • IWT SBO 120003 “SEARCH” WP1.1.2 ACOUSTIC SURVEY TECHNIQUES

    4

    2.1 Sound wave basics and properties Waves are disturbances or vibrations that travel through the space transferring energy from

    one point to another, often with no permanent displacement of the particles of the

    medium. Sound waves, in particular, are waves that are not capable of transmitting its

    energy through a vacuum, therefore, they require a transmission medium to occur.

    In general, all waves can be described by the following properties:

    Wavelength: The distance between successive repetitions of the waveform.

    Wavenumber: number of waves per unit distance.

    Amplitude: It can be described as the strength or power of a wave signal. More simply it can

    be defined as the maximum positive (or negative) displacement of a particle from its

    undisturbed position.

    Period: The time between successive repetitions of the waveform. Measured in seco

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