Swath Bathymetry Systems Flashcards
What is Bathymetry?
The measurement of water depths
What is Swath Bathymetry?
The measurement of multiple depths across a swath of the seabed
What are the 5 key components of a Swath Bathymetry System?
- Swath Transducer
- Vessel Motion and Positioning Sensor
- PC to control data recording and acquisition
- Mini SV probe at the transducer location
- SV probe for water column measurements
How many transducer faces are there?
2
What does the motion sensor correct for?
Heave, Pitch & Roll
What is sound velocity used for?
Correcting for changing densities
What are the 4 most common data types obtained by a swath bathymetry system?
- Seabed Profile Data
- Depth Data
- Merged Depth and Amplitude Data (Reflectivity)
- Backscatter Amplitude Data
A swath bathymetry record can be accurately georeferenced provided you have what?
An accurate GNSS system
Give 7 Users of Swath Bathymetry Systems
- Research & Education
- Survey Companies
- Utility Companies
- Marine Science Organisations
- Civil Engineering
- Oil & Gas
- Environmental Organisations
What are the 2 basic types of swath systems?
- Beamformer Systems
2. Interferometric Systems
Is a beamformer or interferometric system more accurate?
A beamformer system
What does a beamformer system measure?
The return time of the reflected signal at a particular, known angle
How is the range determined?
vt/2 where v is velocity and t is travel time
How is depth determined?
R(Sin(o)) where R is the range and o is the angle
How is the range from the transducer determined?
R(Cos(o)) where R is the range and o is the angle
What does an interferometric system measure?
The angle of the reflected signal (because it is not known) at a particular time
What is the distance between the receivers of the transducer known as?
The Transducer Stave Separation
How is the angle determined for an interferometric system?
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
How is the wave length determined?
v/f where v is velocity and f is frequency in Hz
Give 5 advantages of an interferometric system over a standard multibeam
- Cheaper
- Larger Swath
- Good resolution throughout
- Good for shallow water
- Good for flat topography
What impact does SV have on the path of the acoustic pulse?
If it is too high you get a smile and if it is too low you get a frown
What happens if you force the incorrect SV into the data?
You get sound refraction and shifting of depth contours
What is vertical motion?
Heave
What is horizontal motion?
Heading
What is rotational motion?
Pitch and Roll
Why must all sensors be time synchronised?
In order to correctly apply corrections
Seafloor depth is calculated by acquiring what 6 types of data?
- Sound Travel Time
- Sound Velocity
- GPS Position
- Tidal Data
- Transducer Motion
- Vessel Heading
As a rule survey lines should be run in what direction to the shore for MBES?
Parallel
When surveying a channel which direction should the survey lines be run in?
The same direction as the channel
When surveying sound waves which direction should the survey lines be run in and why?
At right angles to the crests to minimise sonar shadows
Why do we need to conduct the patch test?
To re-align the transducer to the sensors and the vessel frame
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?
Time Latency
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?
Pitch Bias
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?
Roll Bias
When conducting the patch test: if 2 lines are run in opposite directions over a target what are you calibrating for?
Heading (Yaw) Bias
