Side Scan Sonar

Question 1

What are the 4 main components of a SSS system?

Answer 1

1. Towfish
2. Stabilising Fins
3. Transducers that transmit obliquely
4. Cable for Power and Data Transmission

Question 2

What is the name of the SSS system that has the largest swath known and what is this swath?

Answer 2

Gloria with a 15km swath

Question 3

When looking at a SSS beam when would it appear most narrow?

Answer 3

When looking from the Top

Question 4

When looking at a SSS beam when would it appear to be widest?

Answer 4

When looking from the front and the sonar beam is titled down

Question 5

What must be taken into consideration when interpreting SSS imagery from the front?

Answer 5

That although the SSS is tilted downwards there will still be some transmission upwards

Question 6

Why is it unrealistic that you will never get no echo?

Answer 6

The seabed is unlikely to ever be completely flat

Question 7

The intensity of what is measured by a SSS system?

Answer 7

Backscatter

Question 8

What 5 things influence the amount of acoustic backscatter?

Answer 8

1. The angle of incidence of the acoustic wave to the seabed
2. The position of the towfish relative to the seafloor
3. The surface roughness
4. The impedance contrast of the water/seabed interface
5. The seabed topography

Question 9

Should there be a good or poor angle of incidence in order to get the best return the towfish?

Answer 9

Good

Question 10

What is true for all shadow zones?

Answer 10

No energy is reflected and the size of the shadow is directly proportional to the size of the feature causing the shadow zone

Question 11

If a shadow is in a hollow area prior to a target what will the return look like?

Answer 11

It will have a weak area of reflection followed by a strong area of reflection

Question 12

If a shadow is after a target what will the return look like?

Answer 12

There will be a strong area of reflection followed by a weak area of reflection

Question 13

Why is uncorrected sonar imagery not a true representation of the seabed?

Answer 13

It is based on time not distance

Question 14

Why do Along-Track Distortions occur?

Answer 14

Because every pulse is sequentially displayed after the other regardless of the towfish speed

Question 15

Why do Across-Track Distortions occur?

Answer 15

Because the data is displayed based on travel time along the slant range from the towfish to the reflection point on the seabed

Question 16

What do Across-Track Distortions cause?

Answer 16

Compression near the the track on the imagery

Question 17

What are the 2 types of Corrections that have to be made in order to produce accurate sonar mosaics?

Answer 17

1. Geometric Corrections

2. Radiometric Corrections

Question 18

What does a Geometric Correction do ?

Answer 18

Change the relative positions of the pixels in the imagery

Question 19

What does a Radiometric Correction do?

Answer 19

Alter the original pixel values so that the relative values of neighbouring pixels are change

Question 20

What are the 4 types of Geometric Correction?

Answer 20

1. Slant Range
2. Anamorphosis (Vessel Speed Changes)
3. Georeferencing
4. Water Column Removal

Question 21

What are the 3 types of Radiometric Correction?

Answer 21

1. Time Variable Gain
2. Removal of Sea Surface Reflections
3. Removal and Filtering of External Noise

Question 22

What does the Slant Range Correction do?

Answer 22

Gives the true range from the towfish to the target

Question 23

What does applying TVG achieve?

Answer 23

A naturally balanced record

Question 24

Give 8 things that can be identified/determined by interpreting a SSS record?

Answer 24

1. Artefacts
2. Refraction
3. Second Sweep Returns
4. Target Height
5. Target Length
6. Noise
7. Quenching
8. First Bottom Return

Question 25

Give 5 applications of SSS

Answer 25

1. Target Location
2. Site Investigations
3. Environmental Surveying
4. Seabed Mapping
5. Fisheries