1. Advanced Remote Sensing
(MSc. in Geoinformatics Engineering)
Presentation on LiDAR Technology
By Mr. Ashenafi B.
(MSc. In Surveying Engineering)
2/3/2021 1

2. 2
2/3/2021
Advanced Remote Sensing for Geoinformatics (MSc.)

3. CONTENTS:
Introduction
Components of LiDAR System
Principles of LiDAR System
LiDAR Geometry
LiDAR Platforms
Types of LiDARS
Typical Lidar Performance Characteristics
Applications
Advantages/Disadvantages
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.) 3

4. Introduction
LiDAR (Light Detection And Ranging) is an active
form of remote sensing method that uses a laser to
measure distances.
Pulses of light are emitted from a laser scanner, and
then the pulse hits a target, a portion of its photons
are reflected back to the scanner.
4
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.)

5. Cont…
Three types of information can be obtained:
a)Range to target
b)Chemical properties of target
c)Velocity of target
Additionally recorded information:
 Angle from nadir of measurement.
 GPS horizontal and vertical positions
 Aircraft Inertial Measurements (pitch, roll, yaw) (50 Hz)
 The time between pulse emission and return are known,
 The directionality of the pulse, and
5
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.)

6. 6
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.)

7. Components of a LiDAR system
 Laser scanner
 GPS Receiver & GPS ground station
 IMU (Inertial navigation measurement unit)
 Data storage and management systems
 High-precision clocks (extremely accurate
clocks and extremely expensive as well).
7
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.)

8. Components of a LiDAR system - Laser
Frequency: 50,000 (50k) to 200,000 (200k) pulses per
second (Hz)
 Wavelength:
 Near-infrared (1-1.5 µm) For Terrestrial Mapping
 Blue-green (0.5 – 0.55 µm) For Bathymetry
 Ultraviolet (0.25 µm) For Meteorology
Eye-safe; low wattage (<1w)
8
2/3/2021
Advanced Remote Sensing for Geoinformatics (MSc.)

9. Meteorology
Bathymetry
9
2/3/2021
Advanced Remote Sensing for Geoinformatics (MSc.)

10. Components of a LiDAR system - Scanner
Mirror spins or scans to project laser pulses to the
surface.
Scanning angles up to 75 degrees; scanner measures
the angle at which each pulse was fired.
Receives reflected pulse from surface (“return”)
10
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.)

11. Components of a LiDAR system - GPS
Global Positioning System (GPS)
- Records the x,y,z location of the scanner
- Surveyed ground base stations in the flight area
Inertial Measurement Unit (IMU)
- Measures the angular orientation of the scanner relative
to the ground (pitch, roll, yaw).
Clock (High-precision clocks)
 Records the time the laser pulse leaves and returns to the
scanner
11
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.)

12. Lidar Operating Principles
 Pulsed system: transmitted signal consists of a series of
laser pulses, 10,000 to 150,000 pulses/second (10 –
150kHz pulse rate).
 Range to target calculated from time to receive pulse.
Range = c*t / 2
 Wavelengths utilized: 1.0 - 1.5µm (terrestrial studies)
:0.50-0.55 µm (bathymetric studies)
12
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.)

13. Principles of Airborne LiDAR – Flight Planning
 Cannot penetrate clouds
 Are often flown at night
 Overlap of 30 to 50% in steeper terrain
 Multiple passes at different angles in urban
areas (to avoid lidar “shadow”)
 Flying elevation typically 200 to 300 meters
(higher in urban areas)
13
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.)

14. 14
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.)

15. LiDAR Resolutions /DEM Resolutions
Laser Field of View (FOV) (or footprint)
Range distance and range resolution
Point density / point spacing
15
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.)

16. LiDAR – FOV (or footprint) Large or Small?
 FOV related to beam divergence (0.1 to 1
milliradian).
 Small FOV for detailed local mapping.
 Large FOV for more complete ground
sampling and more interactions with multiple
vertical structures.
16
2/3/2021
Advanced Remote Sensing for Geoinformatics (MSc.)

17. Pulse laser Range Distance (R) and Range Resolution
(ΔR)
Where;
C: speed of light (~299,792,458 meters/second)
t: time interval between sending/receiving the pulse
(ns)
Δt: resolution of time measurement (ns)
17
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.)

18. Principles of LiDAR – “Resolution”
Higher Resolution and a Narrow FOV is
needed to penetrate dense vegetation.
Higher Resolutions allow the surface and
features on the surface to be better
resolved, but at cost of larger datasets and
slower processing times.
18
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.)

19. Lidar density and DEM resolution
Average of 1 Lidar pulse per DEM pixel
 Point Density (PD)
 Point Spacing(PS)
 PS = Sq.root (1/PD)
Example: 8 pulses / sq.meter = 0.35 meters
19
2/3/2021
Advanced Remote Sensing for Geoinformatics (MSc.)

20. Principles of LiDAR – “Resolution”
20
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.)

21. Principles of LiDAR – Accuracy
 Vertical accuracy typically 15 to 20 cm (~6
inches)
 Horizontal accuracy 1/3 to 1 meter
 Accuracy improved by flying low and slow,
with a narrow FOV
21
2/3/2021
Advanced Remote Sensing for Geoinformatics (MSc.)

22. LiDAR Geometry
2/3/2021 22

23. Canopy Height
2/3/2021 23

24. LiDAR Platforms
Aerial/Aviation(Airborne)
For highly detailed, local elevation data - Small
area where high density is needed
Satellite(space borne)
covers large areas with less detail
Terrestrial(ground spaced)
 Produce detailed 3D models of buildings,
bridges, streetscapes, factories and other man-
made infrastructure.
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.) 24

25. Types of LiDARS
 Based on the Physical Process
 range finders,
 Differential Absorption LIDAR (DIAL)
 Doppler Lidar-
 Based on Scattering Process
 Mie
 Rayleigh
 Raman,
 Fluorescence Lidar
 Based on the Platform
 Ground based
 Airborne
 Spaceborne)
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.) 25

26. Typical Lidar Performance Characteristics
Specification Typical Value
Wavelength 1000-1500 nm
Pulse Rep. Rate 140 kHz
Pulse Width 10 nsec
Scan Angle 40° - 75°
Scan Rate 25 - 40 Hz
Swath Width Up to 0.7 * altitude
Z accuracy RMSE Approx 15 cm
X,Y accuracy RMSE 10 - 100 cm
Footprint 0.25 - 2 m (from1000m)
Resolution 0.75 meters
GPS frequency 1 Hz
IMS Frequency 50 Hz
Operating Altitude 500 - 2000 m
2/3/2021 26
Advanced Remote Sensing for Geoinformatics (MSc.)

27. Comparison of Lidar and Radar
LiDAR RADAR
Uses optical signals (visible, Near IR).
Wavelengths ≈ 1 um
Uses microwave signals. Wavelengths ≈
1 cm. (Approx 100,000 times longer
than Near IR)
Shorter wavelengths allow detection of
smaller objects (cloud particles, aerosols)
Target size limited by longer
wavelength
Focused beam and high frequency permit
high spatial resolution (< 1m horizontal)
Beam width and antenna length limit
spatial resolution (10s of meters).
Nadir looking sensor Side looking sensor.
Limited to clear atmospheric conditions,
daytime or nighttime coverage.
Can operate in presence of clouds.
Daytime or nighttime coverage.
2/3/2021 27
Advanced Remote Sensing for Geoinformatics (MSc.)

28. Lidar Applications
 Update Digital Elevation Models (DEM)
 „„Glacial Monitoring
 „„Detecting Faults and measuring uplift
 „„Forest Inventory
 „„Shoreline and Beach Volume Changes
 „„Bathymetric Surveying
 „„Landslide Risk Analysis
 „„Habitat Mapping
 „„
Telecom Planning
 „„Urban Development
28
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.)

29. Advantages of LIDAR technology
 Lidar Technology Has Some Advantages
Which Are Listed Below:
 Higher Accuracy
 Fast Acquisition And Processing
 Minimum Human Dependence
 Weather/Light Independence
 Canopy Penetration
 Higher Data Density
 Cost (Comparable).
2/3/2021
Advanced Remote Sensing for Geoinformatics (MSc.)
29

30. Disadvantages of LiDAR technology:
High operating costs (> £10k/hour)
Ineffective during heavy rain and/or low
cloud/mist
Degraded at high Sun angles and reflections
Latency data not processed locally
Unreliable for water depth (< 2m) and breaking
turbulent waves
Lack of foliage/vegetation penetration
Precise alignment must be maintained.
2/3/2021
Advanced Remote Sensing for Geoinformatics (MSc.)
30

31. 31
2/3/2021 Advanced Remote Sensing for Geoinformatics (MSc.)