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Marine Geomatics > Swath Bathymetry Systems > Flashcards

Swath Bathymetry Systems Flashcards

1
Q

What is Bathymetry?

A

The measurement of water depths

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2
Q

What is Swath Bathymetry?

A

The measurement of multiple depths across a swath of the seabed

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3
Q

What are the 5 key components of a Swath Bathymetry System?

A
  1. Swath Transducer
  2. Vessel Motion and Positioning Sensor
  3. PC to control data recording and acquisition
  4. Mini SV probe at the transducer location
  5. SV probe for water column measurements
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4
Q

How many transducer faces are there?

A

2

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5
Q

What does the motion sensor correct for?

A

Heave, Pitch & Roll

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6
Q

What is sound velocity used for?

A

Correcting for changing densities

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7
Q

What are the 4 most common data types obtained by a swath bathymetry system?

A
  1. Seabed Profile Data
  2. Depth Data
  3. Merged Depth and Amplitude Data (Reflectivity)
  4. Backscatter Amplitude Data
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8
Q

A swath bathymetry record can be accurately georeferenced provided you have what?

A

An accurate GNSS system

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9
Q

Give 7 Users of Swath Bathymetry Systems

A
  1. Research & Education
  2. Survey Companies
  3. Utility Companies
  4. Marine Science Organisations
  5. Civil Engineering
  6. Oil & Gas
  7. Environmental Organisations
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10
Q

What are the 2 basic types of swath systems?

A
  1. Beamformer Systems

2. Interferometric Systems

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11
Q

Is a beamformer or interferometric system more accurate?

A

A beamformer system

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12
Q

What does a beamformer system measure?

A

The return time of the reflected signal at a particular, known angle

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13
Q

How is the range determined?

A

vt/2 where v is velocity and t is travel time

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14
Q

How is depth determined?

A

R(Sin(o)) where R is the range and o is the angle

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15
Q

How is the range from the transducer determined?

A

R(Cos(o)) where R is the range and o is the angle

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16
Q

What does an interferometric system measure?

A

The angle of the reflected signal (because it is not known) at a particular time

17
Q

What is the distance between the receivers of the transducer known as?

A

The Transducer Stave Separation

18
Q

How is the angle determined for an interferometric system?

A

Sin-1 (PD x WL/2 x pi x s) where PD is phase difference, WL is wave length and s is the transducer stave separation

19
Q

How is the wave length determined?

A

v/f where v is velocity and f is frequency in Hz

20
Q

Give 5 advantages of an interferometric system over a standard multibeam

A
  1. Cheaper
  2. Larger Swath
  3. Good resolution throughout
  4. Good for shallow water
  5. Good for flat topography
21
Q

What impact does SV have on the path of the acoustic pulse?

A

If it is too high you get a smile and if it is too low you get a frown

22
Q

What happens if you force the incorrect SV into the data?

A

You get sound refraction and shifting of depth contours

23
Q

What is vertical motion?

A

Heave

24
Q

What is horizontal motion?

A

Heading

25
Q

What is rotational motion?

A

Pitch and Roll

26
Q

Why must all sensors be time synchronised?

A

In order to correctly apply corrections

27
Q

Seafloor depth is calculated by acquiring what 6 types of data?

A
  1. Sound Travel Time
  2. Sound Velocity
  3. GPS Position
  4. Tidal Data
  5. Transducer Motion
  6. Vessel Heading
28
Q

As a rule survey lines should be run in what direction to the shore for MBES?

A

Parallel

29
Q

When surveying a channel which direction should the survey lines be run in?

A

The same direction as the channel

30
Q

When surveying sound waves which direction should the survey lines be run in and why?

A

At right angles to the crests to minimise sonar shadows

31
Q

Why do we need to conduct the patch test?

A

To re-align the transducer to the sensors and the vessel frame

32
Q

When conducting the patch test: if 2 lines are run in the same direction: 1 at high speed and 1 at low speed and there is a slope in the seabed what are you calibrating for?

A

Time Latency

33
Q

When conducting the patch test: if 2 lines are run in opposite directions at the same speed and there is a slope in the seabed what are you calibrating for?

A

Pitch Bias

34
Q

When conducting the patch test: if 2 lines are run in opposite directions at the same speed at the seabed is flat what are you calibrating for?

A

Roll Bias

35
Q

When conducting the patch test: if 2 lines are run in opposite directions over a target what are you calibrating for?

A

Heading (Yaw) Bias

Marine Geomatics (11 decks)

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