LiDAR = Light Detection And Ranging ...also known as LASER altimetry
.. is an increasingly common form of active remote sensing
It is used to create high resolution DEMs: 1 foot - 1 metre (airborne)
Objects reflect more in UV- visible- NIR (than microwaves) and enable higher resolution mapping.
What is LiDAR ?
Controlled bursts of LASER (Light Amplification
by Stimulated Emission of Radiation)
Distance to object given by TIME
- requires 3 units: laser emitter/receiver, GPS,
IMU (Inertial measurement unit)
Used in 60s-70s for scanlines, feasible for
images with development of GPS (1990s)
-now widely commercially available
-Related technologies:
-SONAR SOund NAvigation and Ranging :
sound propagation for communication
and navigation
SODAR: SOnic Detection And Ranging:
sound propagation upwards
(atmospheric)
Range finding LiDAR for topographic mapping
Laser bursts are emitted at these wavelengths: (why these ??? *)
355 nm (UV) 532 nm (green) 1064 nm (Near IR)
Unaffected by clouds above (unlike photos / airborne scanning) .. why?
* [Taser guns are at 650 nm ; phasers at 350nm ]
Note: there are two other types of LiDAR:
Differential Absorption Lidar (DIAL) - - measures chemical concentration
of such as ozone, pollutants, water vapour, by using two wavelengths, one is
partially backscattered, the other not.
Doppler LiDAR (for measuring wind speeds)
Returns give distance (hence heights) for multiple levels:
the only remote sensing technique able to distinguish between multiple ground layers
LiDAR applications: detailed DEMs
http://pugetsoundlidar.ess.washington.edu/example2.htm
http://www.geog.ubc.ca/~olav/publications/Kovanen%20and%20Slaymaker%202004b
http://www.aerometric.com/Gallery/lidar_gallery.html
Mt. St. Helens animation:
http://vulcan.wr.usgs.gov/Volcanoes/MSH/Eruption04/LIDAR/framework.html
Volume estimation:
Ground Zero
http://www.volker-
goebel.de/Lidar.html
Sea Level rise from ICe in Svalbard (SLICES): 20 m interpolated model of Slakbreen
http://geography.swan.ac.uk/glaciology/projects/slices/Lidar/index.htm
Vegetation: Tree Canopy Height
http://quake.wr.usgs.gov/research/geology/lidar/example2.html
Air photo Vegetation surface DSM Bald Earth Model (BEM)
Aleza Lake Research Forest
Oldest research forest in BC, jointly operated by UBC and UNBC
60km north-east of Prince George
Raw Point Files
For individual tree analysis (FUSION/LDV)
Raw Point Files
• For individual tree analysis (FUSION/LDV)
Elevation of lowest point
Canopy Height = Canopy Surface – Bare Earth
675.21m ASL
Elevation of highest point
707.87m ASL
Tree Height ~ 32.66m
Crown Shape ~ Convex (umbrella)
Crown Footprint ~ 11.55m
Canopy Surface Model
Canopy Height Model
Canopy Surface Model
Canopy Surface vs Canopy Height
Tree Stem Maps
Individual tree crowns are discernable from the Canopy Height Model so
we developed a tree finding algorithm to identify tree stem locations
LiDAR Data – tree stems
Tree Stems (displayed by tree height)
Tree Stems (displayed by crown shape)
Stand Level Vertical Return Density Schematic
of a 20m x 20m LiDAR Point Cloud – 400 Pulses
Histogram of Returns (percent)
Stand Level Vertical Return Density Schematic
of a 20m x 20m LiDAR Point Cloud – 400 Pulses
Histogram of Returns (percent)
Stand Level Vertical Return Density Schematic
of a 20m x 20m LiDAR Point Cloud – 400 Pulses
Histogram of Returns (percent)
LiDAR Platforms
Airborne since 1970s e.g. Optech (Ottawa) and NorthWest Geo (Calgary)
Satellite platforms:
ICESat (Jan 2003): Geoscience Laser Altimeter System (GLAS):
66m 'footprint' and 10cm vertical resolution, designed for polar icecaps
CALIPSO: Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation
ALADIN Wind LiDAR
LiDAR summary
Present drawbacks:
o High cost of collecting lidar
o High data volume
o Steep learning curve in research and understanding
(involving utilizing the entire point cloud)
Advantages:
Very high resolution DEM for many applications
Multi-layer data for forestry and ecosystems
Increasing data supply – some free downloads
Increasing conference content in GIS/RS/Cartography
Many online resources e.g. :
USGS: http://lidar.cr.usgs.gov/knowledge.php
BC CARMS: http://carms.geog.uvic.ca/carmslidarnew.html
U of Calgary campus: http://www.ucalgary.ca/map/movie4.html
http://www.youtube.com/watch?v=_myUhYPeAew
Stonehenge http://www.youtube.com/watch?v=pzYUx4l80m8