LiDAR Flashcards
What does LIDAR stand for?
Light Detection and Ranging
What does ALHS stand for?
Airborne Lidar Hydrography System
What does ALBS stand for?
Airborne Lidar Bathymetric System
What does HALB stand for?
Hydrographic Airborne Laser Bathymetry
What does SHOALS stand for?
Scanning Hydrographic Operation Airborne Lidar System
What does LADS stand for?
Laser Airborne Depth Sounder
What 2 light beams are there in a LiDAR system and what does each detect?
Red – topographical data
Green – penetrates the water column and comes back off the seabed (bathymetric data)
How many images can you get in a minute if travelling at 140 knots and emitting 35,000pulses/second?
60
What are the 10 components of the LiDAR System?
- Power Source
- Light Source
- Accurate Timing System
- Optical Sensor
- High Precision Scanner
- Transceiver Unit
- Attitude/Motion Sensors
- Data Storage
- Processing Software
- Modern Deliverables
What are the differences in return based on?
The Ellipsoid
Describe the LiDAR process
Known physical properties of light are used, position is given by GNSS, transmitter emits a pulsed laser source, pulse is directed to the water surface/seabed and back into receivers using varied scanner patterns, the returned pulse entry receivers, and is digitised and recorded in binary format
Why are the receivers closed during digitisation?
Because they are photon sensitive
Give 3 examples of the available LiDAR systems
- Fugro LADS MK3
- AHAB Chiroptera II
- Hawk Eye III
What determines footprint size?
The Scan Method/Pattern
What are the 4 Scan Patterns?
- Rectilinear
- Circular Arc
- Elliptical
- Elliptical Arc
What must the flying height be throughout?
Constant
Give 5 things that can impact the laser pulse
- IR at the surface
- Surface Refraction
- Backscatter and Bottom Reflection
- Receiver Field of View
- Environmental Factors
How are predicted depths determined?
2.5x the secchi depth
Give 10 applications of LiDAR
- Port Maintenance
- Wreck Investigations
- Climate Change Mapping
- Mapping Dangerous Areas
- Habitat Mapping
- Coastline Preservation/Sediment Dynamics
- Construction
- Oil and Gas Pipelines
- Tsunami Modelling
- Hazards to Navigation Investigations
Give 8 +ves of LiDAR
- Flexibility and Cost Effective
- Survey Hazardous Areas Safely
- Rapid Mapping
- Lower Carbon Footprint than Vessel Surveys
- Swath not effected by water depth
- Specialised for shallow water
- Collect dense data sets
- Map land and water simultaneously
Give 5 -ves of LiDAR
- Ineffective in turbulent and turbid waters
- Cannot get IHO special order standards
- Ineffective in heavy rain/low cloud
- Unreliable in waters
What must be considered in LiDAR survey planning?
Project area, survey lines, permissions, seasonal weather, best operational airport and terrain and building heights
What 3 things must be considered during LiDAR operations?
- Weather Checks
- Airport Operating Times
- Water Conditions
What are the 5 stages of getting good LiDAR results?
- Know what you want and plan wisely
- Study the survey area
- Mob, Cal and Survey
- Additional surveys (e.g. land survey)
- Data processing and QC
Why would LiDAR and MBES be used together?
To get 100% coverage because they overcome each others limitations
What are the 3 areas of future development?
- Multipulse in Air (MPIA)
- Blue Wavelengths
- Satellite Derived Bathymetry
What are the +ves of using satellite derived bathymetry?
Variety of Satellites and may be rapid
What are the -ves of using satellite derived bathymetry?
Accuracy only 2-3cm and whats in the water?
