vii
TABLE OF CONTENTS
CHAPTER
1
TITLE
PAGE
TITLE PAGE
i
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENTS
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
xii
LIST OF FIGURES
xiii
LIST OF SYMBOLS
xviii
LIST OF ABBREVIATIONS
xx
LIST OF APPENDICES
xxii
INTRODUCTION
1
1.1 Background
1
1.2 Research Problem
3
1.3 Aim of the Research
6
1.4 Research Objectives
7
1.5 Research Scope
7
1.6 Significance and Contributions of the Study
8
1.7 Review of the Relevant Literature on Refraction Issue
in MBES
1.8 Summary
9
13
viii
2
PRINCIPLE OF MULTIBEAM ECHOSOUNDING
14
2.1 Characteristics of the Acoustic Wave
14
2.2 Sound Wave in the Hydrographic Medium
15
2.2.1 Properties of Seawater Affecting Speed of Sound
15
2.2.1.1 Temperature
15
2.2.1.2 Salinity
16
2.2.1.3 Pressure
17
2.2.1.4 Density
17
2.2.2 Sound Speed Measurements in Water
18
2.2.3 Sound Speed Variability in the Ocean
18
2.2.3.1 Sound Speed Layers in the Oceans
19
2.3 Equation for Speed of Sound in the Water
22
2.4 Multibeam Echosounder Systems
27
2.4.1 Introduction
27
2.4.2 Principle of MBES Operation
28
2.4.3 Transducer
29
2.4.4 Transducer Arrays
30
2.4.4.1 Flat Array Transducers
31
2.4.4.2 Curved array Transducers
33
2.5 Beam Steering in MBES
34
2.6 Beam Steering in Flat Arrays
34
2.6.1 Mechanical Beam Steering
35
2.6.2 Electronic Beam Steering
35
2.6.2.1 Time Delay Method
37
2.6.2.2 Phase Delay Method
38
2.6.2.3 Fast Fourier Transformation Method
38
2.7 Beam Steering in Curved Arrays
39
2.8 Ray Tracing
41
2.8.1 Introduction
41
2.8.2 Vertical Incidence
42
2.8.3 Oblique Incidence
42
2.8.3.1 Layers with Constant Sound Speed
44
2.6.3.2 Layers with Constant Sound Speed Gradient
45
ix
2.9 Sound Speed Measurements in MBES
48
2.9.1 Surface Sound Speed (SSS)
49
2.9.2 Sound Velocity Profile (SVP)
49
2.10 Errors in Multibeam Systems
50
2.10.1 Introduction
50
2.10.2 What are the Largest Errors?
51
2.10.3 Does our Sound Speed Measurements
Adequate Enough?
2.10.4 Refraction in Multibeam Echosounders
3
51
52
2.10.4.1 Introduction
52
2.10.4.2 Effects during the Beam Steering
53
2.10.4.3 Effects Through the Water Column
54
2.11 Summary
55
FIELD DATA COLLECTION
56
3.1 Introduction
56
3.2 Survey Instrumentation
56
3.2.1 The MBES system
56
3.2.2 The Single Beam Echosounder (SBES)
57
3.2.3 The Positioning System
58
3.2.4 Sound Speed Measurements
59
3.2.4.1 SSS Measurements
59
3.2.4.2 SVP Measurements
60
3.2.5 Motion (Attitude) Sensor
61
3.2.6 Tide Gauge
61
3.3 Survey Software
62
3.4 Survey Platform
63
3.5 Field Data Collection
64
3.6 Methodology for Determination of Inadequate
Sound Speed Measurements in MBES
65
3.6.1 The Effects of Inadequate SSS on MBES
65
3.6.1.1 Simulated Data Case for SSS
65
3.6.1.2 Real Data Case for SSS
66
x
3.6.2 Determination of Inadequate Sound Velocity
Profile (SVP) Effects on MBES
67
3.6.2.1 Simulated Data Case for SVP
68
3.6.2.2 Real Data Case for SVP
69
3.7 Comparison of SSS and SSVP in Determination of
4
5
6
Snell’s Refraction Constant for Refraction Reduction
70
3.7.1 Data Collection for Refraction Reduction
70
3.7.2 Raw Data Extraction
71
3.7.2.1 MBES Data
71
3.7.2.2 Transducer Position Data
72
3.7.2.3 Vessel Attitude Data
73
3.7.2.4 SBES DTM Data
74
COMPUTER PROGRAM DEVELOPMENT
76
4.1 Introduction
76
4.2 The SSS Program
76
4.3 The Algorithm of the SSS Program
89
4.4 The SSVP Program
92
4.5 The Algorithm of the SSVP Program
92
DATA PROCESSING
94
5.1 Programme Validation
94
5.2 Data Processing
94
5.2.1 MBES Data Processing
94
5.2.2 SBES Data Processing
97
5.2.3 Final Comparison
99
RESULTS AND ANALYSIS
102
6.1 Introduction
102
6.2 Results of Program Validation
102
6.2.1 Northing Comparison
103
6.2.2 Easting Comparison
104
6.2.3 Depth Comparison
106
xi
6.2.4 Summary of Program Validation
6.3 Inadequate SSS Effects on Flat Array MBES Transducers
107
108
6.3.1 Synthetic Data Results
108
6.3.2 Real Data Results
110
6.3.3 Summary of Inadequate SSS Effects on
Flat Array MBES Transducers
6.4 Inadequate SVP Effects on Flat Array MBES Transducers
111
112
6.4.1 Synthetic Data Results
113
6.4.2 Real Data Results
114
6.4.3 Summary of Inadequate SVP Effects on
Flat Array MBES Transducers
6.5 Refraction Reduction Results
7
115
116
6.5.1 Nadir Comparison
116
6.5.2 Outer Comparison
118
6.5.3 Summary of Refraction Reduction Results
120
CONCLUSION AND RECOMMENDATIONS
121
7.1 Conclusion
121
7.2 Recommendations
122
REFERENCES
124
Appendices A-E
128-145
xii
LIST OF TABLES
TABLE NO.
TITLE
PAGE
2.1
Table of coefficients (UNESCO Equation)
25
2.2
Table of coefficients (Grosso’s Equation)
27
3.1
Sound speed configurations to determine the SSS effects
in the simulated data case
3.2
SSS and SVP configuration to determine the SSS effects
in the real data case
3.3
67
Sound speed configurations to determine the SVP effects
in the simulated data case
3.4
66
69
SSS and different SVP configurations to determine the SVP
effects in the real data case
70
xiii
LIST OF FIGURES
FIGURE NO.
1.1
TITLE
PAGE
Illustration of how refraction degrade the accuracy of
MBES data
5
1.2
Observe the parallel ridges and valleys due to sound speed errors
5
2.1
Variation of water temperature with depth in Labrador Sea, Canada
16
2.2
Variation of water salinity with depth in Labrador Sea, Canada
17
2.3
Example of sound speed profiles and it’s diurnal variation
19
2.4
Oceanic water layers and example deep-sea SVP
20
2.5
Typical temperature and salinity variations as a function of depth
21
2.6
The complexity of the oceanography of coastal water masses
22
2.7
MBES beam footprint and swath coverage
29
2.8
Beam forming in flat transducer arrays
30
2.9
Beam footprints resulting from the intersection of transmission
and reception in RESON SeaBat 8124 MBES
32
2.10
Example for flat transducer arrays
32
2.11
Curved or Barrel type transducer array
33
2.12
Typical examples of curved transducer arrays
34
2.13
Electronic Beam Steering
36
2.14
Applied delays to individual transducer elements to detect
oblique beams
37
2.15
Stave selection for beam steering in curved transducer array
39
2.16
Weights added to the neighbourhood and outermost beams
have to be steered
2.17
2.18
40
Outer beams steered using the physical shape of the transducer
combined with electronic steering
40
Ray tracing in MBES
41
xiv
2.19
Illustration of oblique incidence
43
2.20
Modelling the sound speed profile in the water
44
2.21
Ray path in a constant sound speed gradient layer
46
2.22
Cross-section of the sound speed structure on the edge of
Georges Bank
52
2.23
Refraction effects in each phase of the MBES
52
2.24
Effect of change in SSS in beam pointing angle in a flat array
transducer: In the case of true SSS is greater than the measured value 54
3.1
The MBES System
57
3.2
The SBES System
58
3.3
The DGPS System
58
3.4
The SSS Probe
59
3.5
The SVP Probe
60
3.6
MAHRS Attitude Sensor
61
3.7
Tide Gauge
62
3.8
QINSy console
63
3.9
Survey Platform
64
3.10
Survey areas
65
3.11
Altering the SSS value in the sonar processor
67
3.12
Synthetic two-layered SVP
68
3.13
SVPs used to determine the SVP effects in the real data case
69
3.14
Selected data items in each MBES beam
71
3.15
Exported raw MBES data string
72
3.16
Selected raw data items in transducer positions
72
3.17
Exported Transducer Position data string
73
3.18
System selection (MRU) in analyse
74
3.19
Exported raw attitude data string
74
3.20
Selected data source and parameters in SBES DTM
75
3.21
SBES DTM data string
75
4.1
Conversion of total samples to travel time
77
4.2
Interpolation of roll, heave and pitch with respect to each ping time
77
4.3
Flowchart for the calculation of effective beam angle
78
4.4
Flowchart for the calculation of net pitch angle
79
xv
4.5
Flowchart for the calculation of final beam direction
4.6
Flowchart for the calculation of the Snell’s refraction constant
using surface sound speeds
4.7
80
Flowchart for the calculation of the sound speed layer number
and travel time up to (N-1) sound speed layer
4.8
79
81
Flowchart for the calculation of the travel time in the last
sound speed layer
82
4.9
Calculation of the range distance in the last sound speed layer
82
4.10
Flowchart for the calculation of the depth in the last
sound speed layer
4.11
Flowchart for the calculation of the final reduced depth
of each beam
4.12
5.1
91
Flowchart for the calculation of the Snell’s refraction constant
using SSVP
4.21
89
Algorithm for bathymetric calculations using the SSS in
refraction constant
4.20
88
Flowchart for the calculation of the final Easting and
Northing for each beam
4.19
87
Flowchart for the calculation of the Easting and Northing
differences with respect to the sonar head position for each beam
4.18
87
Flowchart for the calculation of the corrected total across track with
respect to the corrected beam direction for each beam of each ping
4.17
86
Flowchart for the calculation of the corrected beam direction
with respect to the sonar head position for each beam of each ping
4.16
85
Flowchart for the calculation of the total across track for
each beam of each ping
4.15
84
Flowchart for the calculation of the across track distances
for each beam at the last sound speed layer
4.14
83
Flowchart for the calculation of the total across track distance up to
(N-1) sound speed layer for each beam from the sonar head position
4.13
83
92
Algorithm for bathymetric calculations using SSVP
in the refraction constant
93
Final MBES coordinate conversion
95
xvi
5.2
Processed MBES bathymetric data from the program output
loaded in to AutoCAD as a multiple point script file
96
5.3
Quicksurf software loaded in AutoCAD R14
96
5.4
Generated DTM for the first MBES data set using Quicksurf
97
5.5
SBES Script (SCR) generation
98
5.6
SBES profile after running the script file in AutoCAD
98
5.7
Loaded data sets to AutoCAD
99
5.8
Generated profiles are saved as blocks with a reference (base) point
100
5.9
Loaded profile blocks in to a single drawing for the comparison
101
5.10
All the blocks are overlaid each other using the common
base point in the final comparison
6.1
Northing coordinate comparison between QINSy vs. SSVP
programmes for the first ping
6.2
104
Easting coordinates comparison between QINSy vs. SSVP
for the first ping
6.4
103
Northing coordinate comparison between QINSy vs. SSVP
programmes for the second (200th) ping
6.3
101
105
Easting coordinates comparison between QINSy vs. SSVP
for the second (200th) ping
105
6.5
Depth comparison between QINSy vs. SSVP for the first ping
106
6.6
Depth comparison between QINSy vs. SSVP for the
second (200th) ping
6.7
107
Variation of the magnitude of the angular error with respect to the
beam-pointing angle for different SSS variations
108
6.8
Across track errors for 100m flat sea bottom for different SSS errors
109
6.9
Depth errors for 100m flat sea bottom for different SSS errors
109
6.10
Impact on the shape of the swath for different SSS errors
on a flat sea floor from a flat MBES
110
6.11
Real examples for SSS variation effects on a flat array MBES swath
111
6.12
IHO error budgets for different levels of surveys
112
6.13
Depth errors due to 10m/s SVP variation at the first 10m layer
of the SVP for a 100m deep, flat sea bottom
113
xvii
6.14
Across track errors due to 10m/s SVP variation at the first
10m layer of the SVP for a 100m deep flat sea bottom
6.15
113
Impact of the sound velocity profile errors on the swath shape
of a flat 100m deep sea floor due to 10m/s SVP variation at the
first 10m layer of the SVP
6.16
114
True examples for SVP variation effects on swath
in a flat array MBES
115
6.17
SSS and SSVP profiles at the nadir from the MBES line 01
117
6.18
SSS and SSVP profiles at the nadir from MBES line 02
117
6.19
SSS, SSVP and corresponding SBES profile comparison
at the outer edge of the swath of MBES line 01
6.20
118
SSS and SSVP outer beam profiles for MBES line 01 and
corresponding SBES and adjacent MBES nadir (line 02)
profile comparison
6.21
119
SSS and SSVP outer beam profiles for MBES line 02 and
corresponding SBES and adjacent MBES nadir (line 01)
profile comparison
119
xviii
LIST OF SYMBOLS
B
-
Bulk modules
C, C, c -
Speed of sound
C0
-
Sound speed at the transducer face
C1
-
Incorrect sound speed measured at the transducer face
Ci
-
Sound speed at the ith layer
D
-
Depth
d
-
Element spacing
E
-
Easting
f
-
Frequency
gi
-
Gradient of the sound speed
h
-
Depth of the sound speed layer
N, N
-
Northing
n
-
Number of elements in the transducer array
Ri
-
Radius of the curvature at the sound speed layer
P
-
Pressure
p
-
Density
R
-
Range
S
-
Salinity
T
-
Temperature
t
-
Time
v
-
Sound speed of each layer
x
-
Horizontal distance
Δi
-
Layer thickness
Δϕ s
-
Phase shift for the ith element
λ
-
Wave length
μ
-
Harmonic mean speed of sound
xix
θ
-
Beam angle
θs
-
Steering angle
ρ
-
Snell’s refraction coefficient
xx
LIST OF ABBREVIATIONS
ASCII
-
American Standard Code for Information Interchange
AutoCAD
-
Automatic Computer Aided Design
CoG
-
Centre of Gravity
CTD
-
Conductivity Temperature Density
CSV
-
Comma Separated Values
Db
-
Database
DGPS
-
Differential Global Positioning System
DTM
-
Digital Terrain Model
DWG
-
Drawing
DXF
-
Data Exchange Format
EEZ
-
Exclusive Economic Zone
GPS
-
Global Positioning System
IHO
-
International Hydrographic Organisation
MAHRS
-
Meridian Attitude and Heading Reference System
MATLAB
-
Matrix Laboratory
MBES
-
Multibeam Echosounder System
MRU
-
Motion Reference Unit
MVP
-
Moving vessel Profiler
NPL
-
National Physics Laboratory
OMG
-
Ocean Mapping Group
ppt
-
parts per thousand
pps
-
pulse per second
QINSy
-
Quality Integrated Navigation System
QPS
-
Quality Positioning Service
Qsurf
-
QuickSurf
RTKGPS
-
Real Time Kinematic Global Positioning System
SBES
-
Single Beam Echosounder
xxi
SCR
-
Script file
SSS
-
Side Scan Sonar
SSVP
-
Surface value of the Sound Velocity Profile
SVP
-
Sound Velocity Profile
TIN
-
Triangular Irregular Network
TWTT
-
Two Way Travel Time
UNB
-
University of New Brunswick
UNESCO
-
United Nations Educational, Scientific and Cultural
Organization
USACE
-
United States Army Crops of Engineers
XLS
-
Microsoft Excel file
3D
-
Three-dimensional
xxii
LIST OF APPENDICES
APPENDIX
TITLE
PAGE
A
Database Settings
128
B
Synthetic data for SSS case
136
C
Synthetic data for SVP case
137
D
Program validation Results
138
E
Publications
144