2. Contents Introduction General description Brief history
LIDAR platforms Types of LIDAR Basic Principle and techniques How
LIDAR works LIDAR components Some example of LIDAR uses
Applications Advantage Disadvantage Future Scope Conclusion
3. INTRODUCTION LIDAR is an acronym for LIght Detection And
Ranging. It is an optical remote sensing technology that can
measure the distance to or other properties of a target by
illuminating the target with light pulse to form an image.
4. General Description This is an active remote sensing
technique similar to RADAR but uses laser light pulses instead of
radio waves. Most LIDAR systems operate in near infrared range of
electromagnetic spectrum (i.e. 1064 nm). LIDAR instruments can
rapidly measure the earths surface at sampling rates greater than
150 kHz. The resulting product is a densely spaced network of
highly accurate geo-referenced elevation points/point cloud. It can
be used to generate 3-D representation of earth surface.
5. BRIEF HISTORY Searchlights were used to measure the altitude
of clouds. Measurement was done by pointing a beam of light in sky
and then reading the angle at which the beam light stuck the cloud.
On a device that was a known distance away from the search light
one was then able to obtain height by triangulation. First laser
based searchlight was constructed by G.Fiocco at MIT using a ruby
laser. From there the development of LIDAR sky rocketed.
6. LIDAR PLATFORMS Airborne topographic LIDAR systems are most
common LIDAR systems. The combination of an airborne platform and a
scanning LIDAR sensor is an effective and efficient technique for
collection of elevation data across tens to thousands of square
miles. LIDAR was first developed as a fixed position ground based
instrument for studies of atmospheric composition, structure,
clouds and aerosols. Modern navigation and positioning system
enable use of water-based and land- based mobile platforms to
collect LIDAR data. Airborne LIDAR data are obtained by mounting a
system inside an aircraft and flying over targeted areas.
7. TYPES OF LIDAR There are two basic types of LIDAR- Airborne
LIDAR Terrestrial LIDAR
8. Airborne LIDAR With airborne LIDAR, the system is installed
in either a fixed-wing aircraft or helicopter. The infrared laser
light is emitted toward the ground and returned to the moving
airborne LIDAR sensor. There are two types of airborne sensors:
Topographic LIDAR Bathymetric LIDAR
9. Topographic LIDAR Topographic LIDAR can be used to derive
surface models for use in many applications, such as forestry,
hydrology, geomorphology, urban planning, landscape ecology,
coastal engineering, survey assessments, and volumetric
calculations.
10. Bathymetric LIDAR Bathymetric LIDAR is a type of airborne
acquisition that is water penetrating. Most bathymetric LIDAR
systems collect elevation and water depth simultaneously, which
provides an airborne LIDAR survey of the land- water interface.
With a bathymetric LIDAR survey, the infrared light (traditional
laser system) is reflected back to the aircraft from the land and
water surface, while the additional green laser travels through the
water column. Analyses of the two distinct pulses are used to
establish water depths and shoreline elevations. Bathymetric
information is very important near coastlines, in harbors, and near
shores and banks. Bathymetric information is also used to locate
objects on the ocean floor.
11. Terrestrial LIDAR Terrestrial LIDAR collects very dense and
highly accurate points, which allows precise identification of
objects. These dense point clouds can be used to manage facilities,
conduct highway and rail surveys, and even create 3D city models
for exterior and interior spaces, to name a few examples. There are
two main types of terrestrial LIDAR: Mobile LIDAR Static LIDAR
12. Mobile LIDAR Mobile LIDAR is the collection of LIDAR point
clouds from a moving platform. Mobile LIDAR systems can include any
number of LIDAR sensors mounted on a moving vehicle. These systems
can be mounted on vehicles, trains, and even boats. Mobile systems
typically consist of a LIDAR sensor, cameras, GPS (Global
Positioning System), and an INS (inertial navigation system), just
as with airborne LIDAR systems. Mobile LIDAR data can be used to
analyze road infrastructure and locate encroaching overhead wires,
light poles, and road signs near roadways or rail lines.
13. Static LIDAR Static LIDAR is the collection of LIDAR point
clouds from a static location. Typically, the LIDAR sensor is
mounted on a tripod mount and is a fully portable laser-based
ranging and imaging system. These systems can collect LIDAR point
clouds inside buildings as well as exteriors. Common applications
for this type of LIDAR are engineering, mining, surveying, and
archaeology.
14. Basic Principles and Techniques The basic idea is fairly
straightforward- Laser generates an optical pulse. Pulse is
reflected off an object and returns to the system receiver.
High-speed counter measures the time of flight from the start pulse
to the return pulse. Time measurement is converted to a distance
(i.e. the distance to the target and the position of airplane is
then used to determine the deviation and location).
15. Working of LIDAR-
16. How LIDAR works Laser produces optical pulse. Pulse is
transmitted, reflected & returned to the receiver. Receivers
accurately measure the travel time. X,Y,Z ground coordinate can be
calculated using : 1. Laser range 2. Laser scan angle 3. Laser
position from GPS 4. Laser orientation form INS.
17. COMPONENTS LIDAR has four components: Laser. Scanner and
optics. LIDAR sensor and photo detectors. Position and navigation
systems.
18. Laser Airborne LIDAR systems use 1064nm diode pumped YAG
lasers while bathymetric systems use 53 nm double diode pumped YAG
lasers.
19. LIDAR Scanner and Optics The speed at which images can be
developed is affected by the speed at which it can be scanned into
the system. Moreover, optic choice affects the angular resolution
and range that can be detected.
20. LIDAR sensors and Photodetectors The HDL-64E LIDAR sensor
is designed for obstacle detection and navigation of autonomous
ground vehicles and marine vessels. Its durability, 360 field views
and very high data rate makes this sensor ideal for 3D mobile data
collection and mapping applications. Two main photo detector
technologies are used in LIDARS: 1. Solid state photo
detectors(e.g.:- silicon avalanche photodiodes). 2.
Photomultipliers.
21. Position and Navigation System When a LIDAR sensor is
mounted on a mobile platform such as airplanes or automobiles, it
is necessary to determine the absolute position and orientation of
the sensor to retain usable data. For this, we have two techniques:
GPS(Global Positioning System) IMU(Inertial Measurement Unit)
22. Some examples of LIDAR use:
23. Applications A LIDAR has the following main applications:
Agriculture Biology and Conservation Wind farm optimization Law
enforcement
24. Agriculture LIDAR can be used to help farmers determine
which areas of their fields to apply costly fertilizer to achieve
highest crop yield. It can create a topographical map of the fields
and reveals the slopes and sun exposure of the farm land.
25. Biology and Conservation LIDAR has also found many
applications in forestry. Canopy heights, biomass measurements
& leaf area can all be studied using LIDAR systems. It is also
used by many industries, including Energy, Railroad & the
Department of Transportation as a faster way of surveying.
Topographic maps can also be generated readily from LIDAR.
26. Wind farm optimization LIDAR can be used to increase the
energy output from wind farms by accurately measuring wind speeds
and wind turbulence. An experimental LIDAR is mounted on a wind
turbulence rotor to measure oncoming horizontal winds, and
proactively adjust blades to protect components and increase
power.
27. Law enforcement LIDAR speed guns are used by the police to
measure the speed of vehicles for speed limit enforcement
purposes.
28. Advantages The other methods of topographic data collection
are land surveying, GPS, interferometry & photogrammetry. LIDAR
technology has some advantages in comparison to these methods
listed below: Higher Accuracy Fast Acquisition and Processing
Minimum human dependence- As most of the processes are automatic
unlike photogrammetry, GPS or land surveying.
29. Weather/Light Independence- Data collection independent of
sun inclination and at night and slightly bad weather. Canopy
Penetration- LIDAR pulses can reach beneath the canopy thus
generating measurements of points there unlike photogrammetry.
Higher data density- Up to 167,000 pulses per second. More than 24
points per meter sq. can be measured in multiple returns to collect
data in 3D. Cost- It has been found by comparative studies that
LIDAR data is cheaper in many applications. This is particularly
considering the speed, accuracy & density of data.
30. Disadvantages High operation costs (Rs. 10 Lacs /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(