vii
TABLE OF CONTENTS
A PTER
TITLE
PAGE
TITLE PAGE
i
AUTHOR’S DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
xii
LIST OF FIGURES
xiii
LIST OF ABRREVIATIONS
LIST OF APPENDICES
1
xviii
xx
INTRODUCTION
1.1
Background of Study
1
1.1.1
3
Acoustic Remote Sensing Technique in Seafloor
Study
1.1.1.1 Multibeam Side Scan (MB SS)
4
1.1.1.2 Seafloor Backscatter Envelopes (Snippets)
5
1.1.2
Correcting the Multibeam Snippets Data
7
1.1.3
Statistical Analysis of Multibeam Snippets Data
8
in Shallow Water
1.2
Problem Statements
8
1.3
Objectives
9
1.4
Scope of Study
10
1.5
Significance of Study
10
viii
2
1.6
Thesis Layout
11
1.7
Contributions of Research
12
1.8
Summary
12
MULTIBEAM ACOUSTIC BACKSCATTERING
2.1
Introduction
13
2.2
Sea Water Acoustic Waves and Physical Characteristics
14
2.2.1
Acoustic Field
15
2.2.2
Sound Speed Measurements in Water
16
2.3
2.4
Acoustic Remote Sensing
16
2.3.1
Vertical-Incidence Sonar Approach
18
2.3.2
Side Scan Sonar Approach
18
2.3.3
Multibeam Sonar Approach
20
Multibeam Echosounder Systems (MBES)
21
2.4.1
22
Principle of Multibeam Echosounder
Systems Operation
2.4.2
2.5
2.6
2.7
Transducer Arrays
22
2.4.2.1 Flat Array Transducer
23
Principles of Acoustic Backscatter
24
2.5.1
Introduction
24
2.5.2
Scattering o f Sound from the Seafloor
28
2.5.3
Seafloor Backscatter Strength
30
2.5.4
Physical Properties of the Seafloor
31
2.5.5
Angular Dependence of Acoustic Backscatter
33
Classification o f Multibeam Backscatter Data
37
2.6.1
Seafloor Terrain Characteristics
38
2.6.2
Analysis of Backscatter Mosaics
38
Modelling Seafloor Backscatter Strength
39
2.7.1
Statistical Analysis of Multibeam Backscatter Data 42
2.7.2
Theoretical Models
43
2.7.2.1 Rayleigh Distribution Model
44
2.7.2.3 Log-normal Distribution Model
44
ix
2.8
Computer Aided Resource Information System (CARIS)
45
2.8.1
45
Total Propagation Uncertainty
(TPU) Filter
2.8.2
Swath F ilter
46
2.8.3
Combined Uncertainty and Bathymetric
47
Estimator (CUBE)
2.9
2.8.3.1 Hypothesis Resolution
48
Bathymetry Associated with Statistical Errors
49
(BASE) Surface
2.10
3
Summary
51
MEASUREMENTS OF MULTIBEAM SNIPPETS DATA
3.1
Introduction
52
3.2
Usage of Multibeam Echo Sounder System
52
3.2.1
54
Reson SeaBat 8124 Multibeam System
Descriptions
3.2.1.1 Phase Detection
56
3.2.1.2 Interferometric Detection
57
3.2.1.3 Pulse Width
58
System Settings
59
3.2.2.1 Transmitting Signal
59
3.2.2.2 Receiving Signal
60
Dynamic Focusing
61
Multibeam Snippets Data Logging
63
3.3.1
Reson SeaBat 8124 Processor Firmware Upgrade
63
3.3.2
81 -P Setup for Snippets and Bathymetric Data
63
3.2.2
3.2.3
3.3
3.4
Preliminary view of determining the Snippets
68
Intensities Target Strength
3.5
4
Summary
71
RADIOMETRIC AND GEOMETRIC CORRECTION OF
MEASURED MULTIBEAM SNIPPETS DATA
4.1
Introduction
72
X
4.2
Radiometric Correction of Measured Multibeam Snippets
74
Data
4.2.1
CARIS Software Processing
74
4.2.1.1 Procedures for CARIS Software
75
Processing
4.2.1.1.1 Vessel Configuration
75
4.2.1.1.2 HIPS Vessel File (HVF)
77
Processing
4.2.1.1.3 Create a New Project
79
4.2.1.1.4 Converting Raw Data
82
4.2.1.1.5 Open a Project
84
4.3
Multibeam Snippets Intensities Data
85
4.4
Removal of System Time Varied Gain (TVG)
88
4.4.1
Time Varied Gain (TVG) Correction
89
4.4.2
Multibeam Snippets Data Corrected for System
95
Settings
4.5
Geometric Correction of Measured Multibeam Snippets
96
Data
4.5.1
Correcting for Local Bottom Slope and Seafloor
96
Insonified Area
4.5.2
4.6
5
Correcting for Angular Dependency
Summary
98
101
SEAFLOOR CLASSIFICATION USING STATISTICAL
ANALYSIS METHOD
5.1
Introduction
102
5.2
Gridding of Multibeam Snippets Data
102
5.3
Statistical Distribution Model in Seafloor
103
Classification
5.3.1
5.4
Gamma Distribution Model
Seafloor Classification using Statistical Analysis
103
106
Method
5.5
Summary
113
xi
6
ANALYSIS ON THE INTENSITIES AND STATISTICAL
VARIATIONS OF MULTIBEAM SNIPPETS DATA
6.1
Introduction
114
6.2
Dependence of Multibeam Snippets Data on the
115
Incidence Angle
6.3
Dependence of the Multibeam Snippets Peak
118
Intensities on Incidence Angle
6.4
Statistical Distribution of the Multibeam Snippets
121
Intensities
6.4.1
Analysis of Data in Fitting with Gamma
121
Distribution Model
6.4.2
6.5
7
Kolmogorov-Smimoff (KS) Statistical Test
Summary
125
128
CONCLUSIONS AND RECOMMENDATIONS
7.1
Conclusions
130
7.2
Recommendations for Future Work
132
REFERENCES
Appendices A -E
133
147-165
xii
LIST OF TABLES
TABLE NO.
2.1
TITLE
Typical values of density, sound speed and resulting
PAGE
29
acoustic impedance for various grades of sediment
2.2
Input parameters for APL model
41
2.3
Different methodologies of BASE surface
50
2.4
The relationship between degree of resolution and
51
depth
5.1
Groups of measured multibeam snippets data
109
6.1
Scale (A) and shape (P) parameters for the fitting
123
with gamma distribution model shown in Figure 6.7
6.2
Statistical distribution functions
125
6.3
Groups of angle domain
126
xiii
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE
1.1
Principle of single beam echo sounder
2
1.2
Principle of multibeam echo sounder
2
1.3
Multibeam Side Scan Sonar Imagery
5
1.4
Multibeam snippets imagery
6
1.5
Derivation of multibeam backscatter imagery
6
1.6
Study area
10
2.1
MBES beam footprint and swath coverage
22
2.2
Beam footprints resulting from the intersection of
23
transmission and reception in RESON SeaBat 8124
MBES
2.3
Example for flat transducer arrays
24
2.4
Spherical spreading o f an acoustic wave
26
2.5
Temperature dependence for oceanic waters (34-36 ppt) 27
2.6
Schematic representation of the reflection,
28
transmission and scattering of acoustic energy at
smooth and rough bottom
2.7
Geometric arrangement for measuring backscatter
31
strength
2.8
Wave phase shift due to seafloor roughness
32
2.9
Surface scattered patterns at oblique incidence
33
(a) A smooth surface reflecting coherently the Incidence
Wave; (b) A rough surface with a large fraction of
acoustic energy scatter incoherently
2.10
Illustration of the -3dB limit from a hypothetical
acoustic beam
34
xiv
2.11
Geometry of incident pulse length on the seafloor for
35
beams at normal and oblique incidence
2.12
Across-track slope is corrected to the angle of
35
incidence with the instantaneous swath profile
2.13
Correction for the angle of incidence using a
36
swath series to determine along-track slope
2.14
CUBE Hypothesis
48
3.1
System performance of Reson SeaBat 8124 system
55
3.2
Phase and amplitude detection
56
3.3
Principle of interferometric detection
57
3.4
Pulse width influence on measurement;
58
a small pulse results in a better resolution than a
large pulse width.
3.5
Sonar head of Reson SeaBat 8124 multibeam
60
system
3.6
TxPower Settings
60
3.7
RxGain Settings
61
3.8
Beam patterns of the Reson SeaBat 8124
62
multibeam system receive array modeled with (green)
and without (blue) dynamic focusing
3.9
BITE display screen
64
3.10
Geo Referencing in backscatter computation setup
64
3.11
Flat bottom assumption
65
3.12
Altitude parameters in backscatter computation setup
66
3.13
Normalization of backscatter data
66
3.14
Channel selection
67
4.1
Work flow of radiometric correction of measured
73
multibeam snippets data
4.2
CARIS HIPS and SIPS 7.0
75
4.3
Caris HIPS and SIPS Vessel Wizard
77
4.4
Vessel File Creation
78
4.5
Vessel in 3D Graphic Display
78
4.6
Project information requirements
79
4.7
Adding created vessel file
80
xv
4.8
Adding day
80
4.9
Description of created proj ect
81
4.10
Selecting UTM zone
81
4.11
Defining the geographic view of project extent
82
4.12
Select format of file to be converted.
83
Select XTF from the list
4.13
Select Navigation Coordinate Type. Choose
83
Ground and UTM-WGS84 Zone 1IN. Accept the
default navigation limits
4.14
Click Convert Side Scan check box and select
84
Sonar Channel 1,2. Set both Navigation data field
and Gyro data field to Ship respectively and select
Apply Image Enhancement
4.15
Window of Open Project
84
4.16
Ship track line of selected project
85
4.17
Measured multibeam snippets intensities data in
86
ASCII format
4.18
Plan view of measured multibeam snippets intensities
87
data
4.19
Plan view of measured multibeam snippets intensities
87
data with different depths interval
4.20
Outliers
88
4.21
Outliers removed
88
4.22
Various gain options
90
4.23
Various losses when the signal travels through the
91
water column and seabed; received levels versus
source levels for an arbitrary model
4.24
Transmission loss as function of the frequency
93
4.25
Signal display window
94
4.26
Signal display window of backscatter intensities
94
(before Time Varied Gain correction)
4.27
Signal display window of backscatter intensities
(after Time Varied Gain correction)
94
xvi
4.28
Plotting of multibeam snippets data (dB) without
95
correction for system settings
4.29
Plotting of multibeam snippets data (dB) after
95
correction for system settings
4.30
Influence of local bottom slopes correction
98
4.31
Before correction for angular dependency
99
4.32
After corrected for angular dependency
99
4.33
Work flow of geometric correction and
100
seafloor classification
5.1
Multibeam snippets data gridded to 1 x 1 meter grid
103
cell size
5.2
Gamma distribution model fitting with snippets data
104
5.3
Grab Sampler
106
5.4
Muddy sea bottom
106
5.5
Snippets intensities plotted map
107
5.6
Selecting desired area (1)
107
5.7
Snippets intensities distribution histogram
108
5.8
Selecting desired area (2)
108
5.9
Snippets intensities distribution histogram
109
5.10
Multibeam snippets data intensities (Group 1)
110
5.11
Multibeam snippets intensities distribution histogram
110
(Group 1)
5.12
Multibeam snippets data intensities (Group 2)
111
5.13
Multibeam snippets intensities distribution histogram
111
(Group 2)
5.14
Multibeam snippets data intensities (Group 3)
112
5.15
Multibeam snippets intensities distribution histogram
112
(Group 3)
6.1
Intensities for inner beams (~ 0°)
115
6.2
Intensities for moderate beams (-3 0 °)
116
6.3
Intensities for oblique beams (~ 60°)
117
6.4
Numerical modelled mean value of the peak
119
intensities versus number of samples
xvii
6.5
Mean intensities strength (peak and average) versus
120
incidence angle
6.6
Skewness squared versus kurtosis of multibeam
122
snippets intensities with different angular domains
6.7
Probability density for multibeam snippets intensities
123
for domains of incidence angles; black line shows the
fitting with gamma distribution model
6.8
The value of gamma shape parameter, p versus
124
incidence angle
6.9
Probability of false alarm fitting with distributions
126
model for normalized multibeam snippets intensities
(near - nadir angle)
6.10
Probability of false alarm fitting with distributions
127
model for normalized multibeam snippets intensities
(moderate angle)
6.11
Probability of false alarm fitting with distributions
model for normalized multibeam snippets intensities
(oblique angle)
127
xviii
LIST OF ABRREVIATIONS
ASCII
-
American Standard Code for Information
Interchange
AUV
Autonomous Operated Vehicle
B.A
-
Backscatter Area
BASE
-
Bathymetry with Associated Statistical Error
BITE
-
Built-In Test Environment
BS
-
Backscatter Coefficient
BTS
-
Bottom Target Strength
CARIS
-
Computer Aided Resource Information System
CDF
-
Cumulative Distribution Functions
CLT
-
Central Limit Theorem
CUBE
-
Combined Uncertainty and Bathymetric
Estimator
DB
-
Decibel
DEM
-
Digital Elevation Model
DNC
-
Digital Nautical Chart
DpTPU
-
Depth Error Estimate
EEZ
-
Exclusive Economic Zone
EL
-
Echo Level
ENC
-
Electronic Navigation Chart
GIS
-
Geographic Information System
GLCM
-
Grey Level Co-Occurrence Matrix
HDCS
-
Hydrographic Data Cleaning System
HIPS
-
Hydrographic Information System
HVF
-
HIPS Vessel File
Hz
-
Hertz
HzTPU
-
Horizontal Error Estimate
xix
IHO
-
International Hydrographic Organization
IL
-
Acoustic Intensity
KS
-
Kolmogorov-Smimoff
MBES
-
Multibeam Echo Sounder
MBSS
-
Multibeam Side Scan
MRU
-
Motion Reference Unit
MSP
-
Method of Small Perturbation
NPD
-
Norwegian Petroleum Directorate
PDF
-
Probability Density Distributions
PPT
-
Parts Per Thousand
RMS
-
Root Mean Square
ROV
-
Remotely Operated Vehicles
RP
-
Reference Point
SBES
-
Single Beam Echo Sounder
SCS
-
Seafloor Classification Systems
SIPS
-
Sonar Image Processing System
SNIPPETS
-
Seafloor Backscatter Envelopes
Std Dev
-
Standard Deviation
SSA
-
Small Slope Approximation
TL
-
Transmission Loss
TPU
-
Total Propagation Uncertainty
TVG
-
Time Varied Gain
XTF
-
Extended Triton Format
XX
LIST OF APPENDICES
APPENDIX
TITLE
PAGE
A
Overall Methodology
147
B
RESON SeaBat 8124 Multibeam Sonar
149
Processor Firmware Upgrade
C
Multibeam Snippets Intensities Data (dB)
151
D
Matlab Code
161
E
Multibeam Snippets Intensities Distribution Map
165