Seabed Classification Flashcards
Give 3 industries that use seabed classification data?
- Nautical Charting
- Commercial and Environmental Surveys
- Military
Give 4 direct methods
- Divers
- Grabs
- Corers
- Dredges
Give 3 remote methods
- Underwater video/photography
- Acoustics
- LIDAR
Give 5 disadvantages of direct methods
- Inefficient data collection
- Expensive per unit area covered
- Environmental Impacts
- Specialised sample analysis
- Time consuming & labour intensive
Remote sensing acoustic seabed classification is the organisation of seabeds into discrete units based on acoustic response which includes what 2 things?
- Acoustic Hardness
2. Physical Roughness
What are the 3 commonly used acoustic methods?
- Quester Tangent (analysis of first echo)
- Roxann Method (analysis for first and second echo)
- Statistical Analysis using SSS and MBES
What are the 3 stages of the Roxann Method?
- Echo Digitisation
- Echo Description
- Echo Classification
What does E1 determine?
Roughness Echo
What does E2 determine?
Hardness Index
Give 3 points about the Reference Catalogue
- It is developed by obtaining information on the seabed using visual and mechanical methods
- Seabed observations are matched to echo responses
- Can be time-consuming - requires groundtruthing and is often unique to the location
What does SSS use?
Raw backscatter and statistics (mean and SD) in cells to determine backscatter characteristics which are compared to the reference catalogue
What is the problem with using backscatter?
The angular dependance on backscatter strength
What is AVG?
Angle-Varying Gain: aims to compensate for across-track variation in backscatter due to physical dependance of the seafloor response with the incidence angle
What does AVG require?
Each data sample to be associated with its angle of incidence to the seabed
How are corrections determine using AVG?
It is looked up in a table that is organised by angle
Give 5 benefits of acoustic seabed classification systems
- Provides remote, real time data acquisition without interfering with normal vessel operations
- Doesn’t impact the seabed itself
- Basic units are comparatively cheap
- Easy to set up and use and are portable
- Can cover large areas efficiently
Give 7 disadvantages of acoustic seabed classification systems
- Constant vessel speed required to provide a constant noise background (usable signal:noise ratio)
- Depth may change results even if bottom type is the same
- Prone to bottom slope effects (especially for 2nd echo methods)
- Affected by bubbles, wakes, acoustic noise and sea state
- For the first and second echo method the sonar range must be set to twice the maximum depth in order to get the 2nd echo
- During data acquisition the sonar settings must remain constant
- Ground thruthing can be time consuming and difficult
