Seafloor Mapping and Bathymetric Sensors
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1
What is the main purpose of bathymetric sensors?
To model the seafloor, detect underwater obstructions, and verify minimum navigational depth\
2
What are the two main categories of seafloor mapping techniques discussed?
Conventional methods and modern techniques\
3
What are the three conventional seafloor survey methods?
Wire drag, wire sweep, and sweep bar\
4
What is the wire drag method?
A horizontal bottom wire of suitable length attached to two ships or boats and set at a desired depth\
5
What supports the horizontal bottom wire in the wire drag method?
Adjustable upright cables suspended from surface buoys\
6
What supports the upright cables in the wire drag method?
Surface buoys\
7
What type of floats are fastened directly to the wire drag bottom wire?
Wooden floats\
8
At approximately what interval are wooden floats fastened to the wire drag bottom wire?
About 30 meters\
9
What keeps the upright cables of a wire drag vertical?
Weights or sinkers attached to their lower ends\
10
What happens to the wire drag wire when it encounters an obstruction?
It becomes taut and forms a V shape\
11
What does the V shape of a wire drag wire reveal?
An underwater obstruction\
12
What are examples of obstructions detected by the wire drag method?
Submerged rocks and wrecks\
13
What advantage does wire drag have over leadlines and sounding poles?
It allows a less laborious and quicker survey\
14
What is the wire sweep method?
A modification of the wire drag method\
15
How do the vertical cables of wire sweep differ from those of wire drag?
Their lengths cannot be adjusted\
16
How are the vertical cables positioned in wire sweep?
Much farther apart\
17
What type of floats are attached between the vertical cables in wire sweep?
There are no intermediate floats\
18
What is one operational advantage of wire sweep over wire drag?
It is faster to put into operation\
19
Where is wire sweep primarily used?
Areas where few obstructions are expected\
20
What water depth is suitable for wire sweep?
Depths greater than those required for navigation\
21
What is a sweep bar made of?
A railroad rail, structural skeletal beam, or steel pipe\
22
How is a sweep bar suspended?
At a predetermined depth by two vertical cables\
23
What is the main purpose of the sweep bar method?
To determine minimum clear depths\
24
Where is the sweep bar method suitable?
River channels and other constricted areas\
25
What type of underwater obstruction is the sweep bar method used to locate?
Minor underwater obstructions\
26
What are the four modern seafloor mapping techniques discussed?
Side-scan sonar, forward-looking sonar, remote sensing, and LiDAR\
27
What are the three components of a side-scan sonar system?
Processing unit, towfish, and transmission cable\
28
What is a towfish?
An apparatus towed behind a boat\
29
What does the towfish of a side-scan sonar system emit?
A transmission signal\
30
What is recorded by a side-scan sonar system?
The returning echo of the signal\
31
Can side-scan sonar determine depth?
No\
32
What were Forward-Looking Sonars (FLS) initially designed for?
Navigation and obstacle or collision avoidance\
33
What additional capabilities do some recent FLS developments offer?
Bathymetric and seafloor classification capabilities\
34
What are the three components of a forward-looking sonar system?
Transducer, power module, and graphical user interface\
35
Where is the transducer of a forward-looking sonar mounted?
At the bow of the vessel\
36
How are forward-looking sonar data displayed?
In 3D through a graphical user interface\
37
Where is forward-looking sonar primarily applied?
Shallow-water navigation\
38
What hazards can forward-looking sonar help reduce?
Oil spills, reef groundings, and whale strikes\
39
What is remote sensing used to obtain in shallow water?
Seafloor classification information\
40
What additional data is required for remote-sensing seafloor classification?
Ground truth data\
41
How do satellites with optical sensors obtain seafloor information?
By analyzing spectral changes\
42
What seafloor information can optical satellite sensors obtain?
Information including depth\
43
What does optical remote sensing use to obtain seafloor information?
The reflectance intensity of different wavelengths of sunlight\
44
What does EMR stand for?
Electromagnetic radiation\
45
Why is optical remote sensing useful in nearshore shallow waters?
Most electromagnetic radiation cannot penetrate deeper water\
46
What is one major limitation of optical remote sensing?
It cannot penetrate through clouds\
47
When is optical remote sensing not very effective?
When the area is heavily covered with clouds\
48
What is another type of satellite sensor used in seafloor mapping?
Synthetic Aperture Radar (SAR)\
49
Where can SAR effectively capture seafloor information according to the lesson?
Farther from the coast\
50
What wavelength scale does SAR use?
Centimeter to meter scale\
51
How does SAR operate?
It transmits electromagnetic waves, detects wavelength changes, and collects and stores echoes for processing\
52
Can SAR penetrate through clouds?
Yes\
53
What is one limitation of SAR imagery?
It provides an unfamiliar view of the area\
54
What does LiDAR stand for?
Light Detection and Ranging\
55
What technology does LiDAR use instead of sound?
Laser technology\
56
What type of LiDAR is used for hydrographic purposes?
Bathymetric LiDAR\
57
What two laser colors are used in bathymetric LiDAR?
Green and red or infrared\
58
What is the typical wavelength of the green laser used in bathymetric LiDAR?
532 nm\
59
What is the purpose of the green laser in bathymetric LiDAR?
To obtain bathymetric data\
60
How deep can the green laser penetrate water according to the lesson?
Up to about 70 meters\
61
What does the green laser reflect off in bathymetric LiDAR?
The seafloor\
62
What is the purpose of the red or infrared laser in bathymetric LiDAR?
To map the adjacent shore's topography\
63
What does the red or infrared laser reflect off?
The water surface\
64
What is one major disadvantage of LiDAR equipment?
It is too costly for most hydrographic survey applications\
65
What is one advantage of LiDAR technology?
It provides promising results in seafloor mapping\
66
In what water conditions is LiDAR not applicable?
Areas with chronic moderate to high turbidity\
67
When should LiDAR operations be scheduled in areas with variable turbidity?
During periods of favorable conditions\
68
What coastal river condition is favorable for LiDAR operations?
Low discharge\
69
What tidal condition is favorable for LiDAR operations?
Neap tide\
70
What is the typical sounding rate of bathymetric LiDAR?
900 Hz or 3.24 million soundings per hour\
71
What is the typical area coverage of bathymetric LiDAR?
20 km² per hour\
72
What is the typical sounding density of bathymetric LiDAR?
5 m × 5 m\
73
What other sounding density capabilities are listed for bathymetric LiDAR?
2 m × 2 m, 3 m × 3 m, and 4 m × 4 m\
74
What is the typical swath width of bathymetric LiDAR?
240 m\
75
At what flight altitude is the listed 240 m swath width achieved?
400 m\
76
What is the bathymetric depth range of LiDAR?
-70 m to -0.5 m\
77
What is the maximum topographic height measured by bathymetric LiDAR?
+50 m\
78
What hydrographic survey standard is specified for LiDAR depth accuracy?
IHO S-44, 4th Edition (1998), Order 1\
79
What is the position accuracy of bathymetric LiDAR?
5 m CEP at 95%\
80
What does CEP stand for?
Circular Error Probable\
81
What does a 5 m CEP at 95% mean?
There is a 95% chance that the true horizontal position lies within a circle of 5 m radius.
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