Swath Bathymetry Systems

Question 1

What is Bathymetry?

Answer 1

The measurement of water depths

Question 2

What is Swath Bathymetry?

Answer 2

The measurement of multiple depths across a swath of the seabed

Question 3

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

Answer 3

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

Question 4

How many transducer faces are there?

Answer 4

2

Question 5

What does the motion sensor correct for?

Answer 5

Heave, Pitch & Roll

Question 6

What is sound velocity used for?

Answer 6

Correcting for changing densities

Question 7

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

Answer 7

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

Question 8

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

Answer 8

An accurate GNSS system

Question 9

Give 7 Users of Swath Bathymetry Systems

Answer 9

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

Question 10

What are the 2 basic types of swath systems?

Answer 10

1. Beamformer Systems

2. Interferometric Systems

Question 11

Is a beamformer or interferometric system more accurate?

Answer 11

A beamformer system

Question 12

What does a beamformer system measure?

Answer 12

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

Question 13

How is the range determined?

Answer 13

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

Question 14

How is depth determined?

Answer 14

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

Question 15

How is the range from the transducer determined?

Answer 15

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

Question 16

What does an interferometric system measure?

Answer 16

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

Question 17

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

Answer 17

The Transducer Stave Separation

Question 18

How is the angle determined for an interferometric system?

Answer 18

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

Question 19

How is the wave length determined?

Answer 19

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

Question 20

Give 5 advantages of an interferometric system over a standard multibeam

Answer 20

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

Question 21

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

Answer 21

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

Question 22

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

Answer 22

You get sound refraction and shifting of depth contours

Question 23

What is vertical motion?

Answer 23

Heave

Question 24

What is horizontal motion?

Answer 24

Heading

Question 25

What is rotational motion?

Answer 25

Pitch and Roll

Question 26

Why must all sensors be time synchronised?

Answer 26

In order to correctly apply corrections

Question 27

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

Answer 27

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

Question 28

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

Answer 28

Parallel

Question 29

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

Answer 29

The same direction as the channel

Question 30

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

Answer 30

At right angles to the crests to minimise sonar shadows

Question 31

Why do we need to conduct the patch test?

Answer 31

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

Question 32

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?

Answer 32

Time Latency

Question 33

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?

Answer 33

Pitch Bias

Question 34

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?

Answer 34

Roll Bias

Question 35

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

Answer 35

Heading (Yaw) Bias