Introduction to LiDAR
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LIDAR is a remote sensing technology that uses laser light to measure distances to the Earth. It can generate highly accurate digital elevation models and other 3D data about physical features and land cover. LIDAR works by measuring the time it takes for a laser to travel from a sensor to the ground and back. This allows it to determine the precise latitude, longitude, and elevation for each point. LIDAR data comes in the form of dense point clouds containing hundreds of thousands or millions of points per square kilometer. LIDAR has many applications, including mapping terrain and creating contours, modeling forests and individual trees, and modeling urban infrastructure for planning and emergency response. Accuracies of LIDAR elevation data are typically
Introduction to LiDAR
- 1. An evolving Remote Sensing tool -Bob Champoux -ICESAT, NASA LIght Detection And Ranging Introduction to LIDAR
- 2. The basics (of Photo Interpretation)…. -Lixin Wang
- 3. What about elevations? Aerial Photo Contours from Photos -Eastern Topographics
- 5. LIDAR Points Each black dot is a LIDAR point •At each point, the elevation has been sampled. Start counting! -GIS Dept. Clinton County, Ohio
- 6. Seeing more than contours…. -GIS Dept. Clinton County, Ohio
- 7. Active Imagery… Three Components: •Laser Scanner •Up to 400,000 pulses/second •Near infrared •Global Positioning System •Positions the scanner •Inertial Navigation System •Orientation of the scanner -Andersen
- 8. -Andersen How LIDAR works The process: •LIDAR sensor measures time from when pulse sent to when received. •This translates to distance from sensor to object. •GPS knows location of sensor. •Coordinates (X,Y,Z) are assigned to each pulse. •Result is a "cloud of points" each point has its own coordinates & height.
- 9. How LIDAR works •So, not only does each dot (sample point) have an elevation. •Each dot has X and Y coords or, Latitude and Longitude •The collected data are hundreds of thousands, sometimes, millions of points. •Each with its own: •Latitude •Longitude •Elevation -GIS Dept. Clinton County, Ohio
- 10. How many points? • Points equals resolution. • Dependent on these variables: • Number of pulses. • Flying height. • Flying speed. • Scan angle. -N. Carolina State University
- 11. Guesses on file size? – Megabytes – Gigabytes – Terabytes -Seagate How LIDAR works
- 12. LIDAR image of Durham, NH -DeLorme
- 13. -GIS Dept. Clinton County, Ohio -Natural Hazards Centre, NZ Triangulated Irregular Network Digital Elevation Model Modeling with LIDAR
- 14. Modeling with LIDAR Contours can be derived -Digital Mapping Australia
- 15. Modeling with LIDAR Oblique view of Wilmington, OH -GIS Dept. Clinton County, Ohio -DeLorme
- 16. Modeling with LIDAR LIDAR image showing all points LIDAR image after removal of trees Digital Elevation Models can be created
- 17. Modeling with LIDAR Develop Watersheds -Instituto Agrario di S. Michele all’Adige
- 18. Map Slopes and Aspect -Free Geography Tools-ESRI Map Slopes Colors relate to Aspect (Direction) Modeling with LIDAR
- 19. Profile View… -GIS Dept. Clinton County, Ohio
- 20. Modeling Forests Canopy Height Model Instead of focusing on the ground… – Measure the heights of the trees. – Canopy height is a critical parameter for ecosystem modeling
- 21. -Digital Mapping Australia Modeling Forests Estimate stand volume and biomass by: – Identify and measure the individual tree crowns. – Individual tree volume and biomass are strongly correlated to the tree’s crown area. – Can look at distribution of volume across the forest. – Aids in forest management
- 22. -Lefsky Other Forest Applications: •Vertical and Horizontal distribution of: •Individual trees •Branches •From this: •Canopy density •Species Identification and Classification •Stand Structure •Successional state •Forest health •Habitats •With time: Change detection Modeling Forests
- 23. -Spencer B. Gross Modeling Individual Trees -Stephen F. Austin State University • With a very high resolution – Individual trees can be mapped.
- 24. -Lefsky LIDAR points Modeling Individual Trees Species can be identified of individual trees
- 25. Modeling Individual Trees Can develop: •Crown base height •Individual tree crowns •3D tree models Subcanopy •Volumes, distribution, etc. The forest floor: •Amount of light reaching the ground. (By studying canopy interception). •Woody debris •Fuel loading
- 27. -OpenTopography Modeling urban areas Uses: •Urban Planning •Transportation •Emergency Response •Drainage Patterns •Flooding •Flooding Response •Amount of Impervious Surface •Vegetation Image above: New Orleans, LA -Terrascan
- 28. Two types of LIDAR sensors • Discrete – Individual points – Small footprint (5-30 cm) – More common sensor -University of Washington
- 29. Two types of LIDAR sensors -CSIRO • Waveform – Continuous vertical return – Better for forest biometrics – Less cost
- 30. -ASPRS Two types of LIDAR sensors • Waveform – Previously: – Large footprint (10’s of m) – Short range -CSIRO
- 31. LIDAR Limitations... Bathymetric and shoreline work is being done with LIDAR that transmits at two wavelengths: •Infrared to detect surface •Green (provides for max. penetration) -Terrascan • Water – Because of using NIR: – Water absorbs signal – Same issue with: – Asphalt – Clouds – Fog, smoke, haze – Rain • Dense Vegetation – May not reach ground – Light may scatter and reflect before returning to sensor (False elevations are the result)
- 32. Why LIDAR now? • History – 1970’s Development began (NASA) – 1980’s GPS incorporated – 1990’s Commercial LIDAR – 2000’s Maturing of technologies: • GPS positional accuracy increases cm level accuracy • INS orientation accuracy increases Pitch/roll accuracy ≈ 0.005º – What’s to come: • More incorporation of LIDAR with other technologies – Digital camera commonly flown with LIDAR • Use of signal intensity • Multiple pulses in the air -GPS satellite
- 33. -Fugro EarthData LIDAR equipment -Wire Services -McKim & Creed
- 34. LIDAR unit in action -ICESAT, NASA Pretty exciting, huh? LIDAR: -Provides the Elevation -Intensity can be measured -DN values
- 35. Accuracies? • Dependent on: – Laser scanner • Range errors – GPS • Position errors – IMU • Orientation errors • For Discreet LIDAR: – 15-30 cm Vertical – 1m Horizontal -USGS
- 36. Accuracies? Other factors affecting LIDAR accuracy: – Steep slopes – Recording of scanner angle – Atmospheric effects -N. Carolina State University
- 37. References • Baltsavais, E.P. (1999). Airborne Laser Scanning: Basic Relations and Formulas. ISPRS Journal of Photogrammetry and Remote Sensing 54 (2/3), 199-214. • Flood, M. and Satalich, J. (3/28/01) LIDAR 101. POB. • Dubayah, R. and Drake, J. LIDAR Remote Sensing for Forestry Applications, College Park, MD, University of Maryland, Department of Geography. • Kraus, K. and Pfeifer, N. (1998) Determination of Terrain Models in Wooded Areas with Airborne Laser Scanning Data. ISPRS Journal of Photogrammetry and Remote Sensing 53 (4), 193-203. • Lefsky, M., Cohen, W., Parker, G. and Harding, D. (2002) LIDAR Remote Sensing for Ecosystem Studies. BioScience 52 (1), 19-30 • CLICK—USGS Center for LIDAR Information Coordination
Editor's Notes
- #3: This and following 2 slides: Remote Sensing so far. Tons of info but no elevational data obtained.
- #4: Contour lines come from aerial photography.
- #5: Elevational info came from manual interpolation methods. Slow and info was basic (e.g. Contour lines)
- #7: Colors keyed to relative elevations
- #11: Dense set of points. Probably from a helicopter-based campaign. Looks like lower area was flown again or slower.
- #12: Terabytes
- #13: Large horizontal swath is a power line. Below it, is Route 4.
- #14: DEM on right is used to determine erosion and cliff collapse potential.
- #16: Lidar “Images” Pawtuckaway State Park on Left
- #18: All the usual DEM products can be created.
- #19: Left-hand image: Scale is percent slope. Right-hand image: Hues relate to aspect. Saturation (Brilliance) represents slope. Brighter color>steeper slope.
- #20: Great slide. Can walk across plan view and see features in profile view.
- #22: This images comes from a study of Biomass and Fuel loading
- #32: Can get returns on water but elevations usually off. Max. depth of bathymetry is 60m
- #37: Can see overlapping flights. Probably a helicopter campaign.