Lidar technology has been used in Nepal for some infrastructure projects previously but the Survey Department of Nepal has now begun a nationwide lidar survey project. The project aims to survey the entire country over the next 7 years which will help with infrastructure development, disaster management, and understanding Nepal's hydropower potential. Lidar uses laser pulses to measure distance and when combined with GPS and image data, can create highly accurate 3D terrain models. The survey data is expected to benefit areas like infrastructure design, flood mapping, and feasibility studies.

1. History of Lidar in Nepal
• Before also, surveying using lidar technology was done but in
some specific areas and purposes. Manakamana cable car,
Bheri Babai diversion, Budhigandaki hydropower,etc are the
projects where Lidar was used.
• In Gandaki river, lidar was also used .

2. • Survey department of Nepal have begin to surveying the Nepal’s physical structure
using LiDAR technology. The survey department have called this as dream project
which will make revolution in infrastructure development, terrain mapping and many
more
• The survey department expect to complete the whole Nepal survey in the next 7
years. Departments expects high and even this surveying will help to know the
feasibility of 83,000 MW of electricity.
• With surveying, the aircraft will also capture the high resolution image of the
mapping area at a time. So the geography digitization using lidar technology will
help for easier survey.

3. • The data extracted by this mapping will be used extensively in infrastructure
designing like road, hydro-power, canal,etc.
• Even, for surveying there wouldn’t need to visit the site.
• Using this surveyed data will help to create feasibility and surveying report.
• This will save a lot of money and time.

4. What is LiDAR ?
• Light Detection And Ranging
• Active Sensing System which uses its own energy source, not reflected natural or
naturally emitted radiation
• Uses light in the form of a pulsed laser to measure ranges (variable distances) to the
Earth. These light pulses combined with other data recorded by the airborne system
generates precise, three-dimensional information about the shape of the Earth and its
surface characteristics.
• A lidar instrument principally consists of a laser, a scanner, and a specialized
GPS receiver.
• Ranging of the reflecting object based on time difference between emission and
reflection. (Multiple Returns per pulse of light)
• Direct acquisition of terrain information
• Highly accurate topographic data
• Can provide information of inaccessible as well as larger areas.
• The wavelength used is 1040 to 1060 nm.(of laser)

5. LiDAR
All reflections of emitted energy are returned, generating a point
cloud of the data
The point cloud contains data points for scan hits at multiple heights
on objects, as well as some noise due to atmospheric conditions.
These hits are referred to as returns and are referenced in ascending
order from highest elevation to lowest elevation for a set of returns
Top of a building or tree is the 1st return
Canopy of a tree or side of a building is 2nd or 3rd return, and so on as the
returned hits descend in elevation
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8. LiDAR Data
All returns
1st return
2nd return
3rd return
4th return
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Image from Lidar Technology Overview, presentation by USGS, June 2007

9. Working Principle
• The position of the aircraft is
known (from DGPS and IMU-
Inertial Measurement Unit).
• Measures distance to surfaces by
timing the outgoing laser pulse and
the corresponding return (s).
Distance = time*(speed of light)/2
• By keeping track of the angle at
which the laser was fired: X, Y, Z
position of each “return” can be
calculated
• Requires extremely accurate timing
and a very fast computer.

11. LiDAR Types
There are two basic types of lidar:
Airborne and Terrestrial
Airborne lidar sensors
1. Topographic:Topographic Lidar uses an infrared wavelength of
1,064nm.
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12. 2. Bathymetric
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Bathymetric Lidar systems use a
green wavelength of 532nm to
penetrate the water column for
measuring the seafloor.

14. How is lidar data collected?
• When an airborne laser is pointed at a targeted area on the
ground, the beam of light is reflected by the surface it
encounters. A sensor records this reflected light to measure a
range. When laser ranges are combined with position and
orientation data generated from integrated GPS and Inertial
measurement Systems, scan angles, and calibration data, the
result is a dense, detail-rich group of elevation points, called a
"point cloud."
• Each point in the point cloud has three-dimensional spatial
coordinates (latitude, longitude, and height) that correspond
to a particular point on the Earth's surface from which a laser
pulse was reflected. The point clouds are used to generate
other geospatial products, such as digital elevation models,
canopy models, building models, and contours.

15. Accuracy
• GPS accuracy 2-5 cm
• INS accuracy for pitch/roll is < 0.005
• Final vertical and horizontal accuracies : order of 5 to 15 cm and 15-
50 cm at one sigma

16. LiDAR Data
LiDAR’s Limitations
Grade breaks – collection pattern is “random” and not based on changes in grade
as a field survey
Critical elevations – may not detect control elevations such as building floor
elevations, edges of concrete, property boundaries or culvert inlet/outlet
elevations (requires local benchmarking at site and adjustment of data to
benchmark)
Vegetation – May affect readings, dependent on quality of the data, density of
vegetation. Tillage(खेनेको खेत) may affect surface smoothness (can affect slope
calculations)
Water – LiDAR can penetrate water, but type of laser and water turbidity can
affect this. Standing water can invalidate a local elevation estimate from LiDAR.
If you believe a data result is due to influence of water, don’t use it for an
elevation
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20. Application
• Digital Elevation Model
• 3D City Modeling
• Forest Inventory Survey/Biomass Estimation
• Hydrology
• Environmental Monitoring
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21. Expectation from Lidar project of Nepal:
• Updating of Existing Topographic Map Data: For the Terai Region, a 1: 25,000 topographic map is
expected to be updated in parallel with the 1: 5,000 topographic map creation. Also, in addition
to the modifications accompanying development, etc., floods, landslides, and other changes also
involve terrain changes, so continuous updating of topographic map data is required. Since the
photogrammetry technology using drones is acquired in the Project, it is expected that existing
topographic map data can be updated not only in the Terai Region but also throughout the
country.
• Improved Disaster Awareness of Relevant Organization and People: A seminar for approx. 60 staff
members of potential user organizations shall be held and the teaching materials and pamphlets
of the seminar shall be prepared in the “Soft Component” of the Project. Through these, public
relations education activities are expected to spread from the Survey Department to the relevant
ministries and agencies, local governments, and even the residents, thereby raising awareness of
disaster prevention.
• Improvement the Accuracy of Identification of Expected Flood Area: By using a detailed DEM,
inundation simulation and calculation of area to inundate and inundation depth are possible,
consequently, reflecting this, it is expected that the accuracy of hazard maps will be improved and
appropriate evacuation plans will be formulated.

22. • Flood control candidate sites such as embankment strengthening points
and flood control reservoirs can be narrowed down. It is expected to be
used for disaster prevention measures, such as identification of danger of
breach of levees, prioritization of countermeasure work, selection of
candidate sites such as flood control reservoirs, etc. based on flow
simulations during river flooding and detailed v topography such as levees.
• Use in Plans for Infrastructure Development (roads, railways, irrigation
canals, etc.) The detailed topographic data and orthophotos to be created
in the Project and the 1/5,000 topographic map data to be created
consequently from them are essential for the preparation and
implementation of infrastructure development plans and the provision of
such data is expected to facilitate the infrastructure development in the
Terai Region.

23. • 3 Types of information can be obtained about target from LIDAR:
• Range: Topographic Lidar, or Laser Altimetry
• Chemical properties of target: Differential Absorption Lidar
• Velocity of target :Doppler Lidar

24. Forest Planning and Management: LIDAR is widely used in the forest industry to plan
and mange. It is used to measure vertical structure of forest canopy and also used to
measure and understand canopy bulk density and canopy base height
Forest Fire Management: LIDAR image helps to monitor the possible fire area which is
called fuel mapping (fire behavior model)
Environmental Assessment: Micro topography data generated form the LIDAR data is
used in the environment assessment. Environment assessment is done to protect the
plants and environment. Remote sensing and surface information (LIDAR) is used to find
the area that is affected by the human activities.
Flood monitoring: LIDAR provides very accurate information. River is very sensitive and
sensitive and few meter of change in information can bring disastrous or loss of
properties. So LIDAR is used to create high resolution and accurate surface model of the
river. These extracted LIDAR information can be used for the 3D simulation for better
planning of the structures or buildings on the river bank.
Application

25. Oil and Gas Exploration: As LIDAR wavelength are shorter, it can be used to detect molecules
content in the atmosphere that has same or bigger wavelength. There is the new technology called
DIAL (Differential Absorption LIDAR) which is used to trace amount of gases above the
hydrocarbon region. This tracking helps to find the Oil and Gas deposits.
Archeology: LIDAR has played important part for the archeologist to understand the surface. As
LIDAR can detect micro topography that is hidden by vegetation which helps archeologist to
understand the surface. DEM created from LIDAR is feed into GIS system and it is combined with
other layer for analysis and interpretation.
Glacier Volume Changes: : LIDAR is used to calculate the glacier change over the period. LIDAR
image are taken in time series to see the change happening. For instance LIDAR image taken at these
time interval are used to estimate the level,area and volume using HECRAS ,GIS.

27. DEM
• DEM is a popular acronym
• Unless specifically referenced as a Digital Surface Model (DSM), the
generic DEM normally implies x/y coordinates and z-values
(elevations) of the bare-earth terrain, void of vegetation and
manmade features.
• According to USGS: DEM is the digital cartographic representation of
the elevation of the land at regularly spaced intervals in x and y
directions, using z-values referenced to a common vertical datum.
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28. 28

29. DTM
• Digital Terrain Models (DTMs) are similar to DEMs in representing the
bare-earth terrain surface but DTM may also incorporate the
elevation of significant topographic features on the land and mass
points and breaklines that are irregularly spaced to better
characterize the true shape of the terrain itself.
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30. DSM
• Digital Surface Models (DSMs) are similar to DEMs or DTMs except
that they depict the elevations of the top surfaces of buildings, trees,
towers, and other features elevated above the bare earth.
• DSMs are especially relevant for telecommunications management,
air safety, forest management, and 3-D modeling and simulations.
• The elevation differences between the DSM and DTM are commonly
used to evaluate the height of vegetation.
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31. LIDAR RADAR
LiDAR stands for Light Detection And Ranging
RADAR stands for RAdio Detection And
Ranging
Short wavelength of light(512nm to 1024nm)
is used.
Long-wavelength microwaves (1mm – 100
cm) is used.
Measures precise distance measurements Measures estimated distance measurements
Used in obtaining 3D images with high
resolution Cannot detect smaller objects.
Down looking sensor Side looking sensor
Limited to clear atmospheric conditions,
daytime or nightime coverage
Can operate in presence of clouds daytime or
nighttime weather
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32. •Active RS: Introduction and types
RADAR: Introduction and
Application
LiDAR: Introduction and
Application

33. • Remote sensing:
Science and art of acquiring information about earth’s surface without
actually being in contact with it.
Types of remote sensing :
-Passive
-Active .

34. • Active Remote Sensing:
Active Remote Sensing is a type of remote sensing that makes use of
sensors able to direct energy in the form of electromagnetic spectrum.i.e
active sensors.
Active sensors provide their own source of illumination which emits
radiations that are directed towards the target body that is to be
investigated.
Active Remote sensors emit energy in order to scan the objects and
areas and they then detect and measure the radiations that are reflected
or are backscattered from the target body.
The sensors transmit short pulses of the electromagnetic energy in the
direction of the target and they record the origin and strength of the
reflected rays received from the object within the system's field of view

35. Types of active remote sensing:
• Active Optical Remote Sensing
• Active Microwave Remote Sensing

36. Active Optical Remote Sensing
.
Active optical remote sensing involves using a laser beam upon a remote target to illuminate it, analyzing the
reflected or backscattered radiation in order to acquire certain properties about the target
. The velocity, location, temperature and material composition of a distant target can be determined using this
method. Example:
LIDAR( Light Detection and Ranging)

37. Active Microwave Remote Sensing
Active microwave remote sensing uses sensors that operate in the microwave region of the
electromagnetic spectrum. Example: RADAR (Radio detection and ranging)
-The sensor transmits a microwave (radio) signal upon a specified
target.
-The reflected or backscattered radiation from the target is then
detected by the active sensors which measure the round trip time delay
to targets allowing the system to calculate the distance of the target from
the sensors.

38. Electromagnetic Spectrum

39. Regions: Optical & Microwaves
Bikash Kumar Karna, Director
Band Designations
(common wavelengths Wavelength () Frequency ()
shown in parentheses) in cm in GHz
____________________________________________
Ka (0.86 cm) 0.75 - 1.18 40.0 to 26.5
K 1.18 - 1.67 26.5 to 18.0
Ku 1.67 - 2.4 18.0 to 12.5
X (3.0 and 3.2 cm) 2.4 - 3.8 12.5 - 8.0
C (7.5, 6.0, 5.6 cm) 3.8 - 7.5 8.0 - 4.0
S (8.0, 9.6, 12.6 cm) 7.5 - 15.0 4.0 - 2.0
L (23.5, 24.0, 25.0 cm) 15.0 - 30.0 2.0 - 1.0
P (68.0 cm) 30.0 - 100 1.0 - 0.3
Visible 0.4 – 0. 7 m
Near Infrared (NIR) 0.7 – 1.5
m
Short Wave Infrared (SWIR) 1.5 – 3 m
Mid Wave Infrared (MWIR) 3-8
m
Long Wave Infrared (LWIR)
(Thermal Infrared (TIR) 8-15
m
Far Infrared (FIR) Beyond 15 m

40. RADAR: Introduction and Application
• RADAR is an acronym for RAdio Detection And Ranging, which
essentially characterizes the function and operation of a radar sensor.
• The sensor transmits a microwave signal towards the target and detects
the backscattered portion of the signal.
• Long-wavelength microwaves (1 mm– 100 cm).
• Use micro waves to detect the presence of objects and to determine
their distance/angular position.

41. • It is basically an electromagnetic system used to detect the
location and distance of an object from the point where it
(RADAR) is placed.
• It works by radiating energy into space and monitoring the echo
or reflected signal from the objects. It operates in the microwave
range.

42. Types of radar :
• Nonimaging radar :Traffic police use handheld Doppler radar
system determine the speed by measuring frequency shift
between transmitted and return microwave signal .
• Imaging radar: Usually high spatial resolution, consists of a
transmitter, a receiver, one or more antennas. For example SAR

43. Radar Components
• It consists of
• a transmitter,
• a receiver,
• an antenna,
• and an electronics system to process and record the data.

44. Radar Basics
 Radar provides its own controllable energy source
 The transmitter generates successive pulses of
microwave (A).
 illuminates the surface obliquely at a right angle to
the motion of the platform(B).
 The antenna receives a portion of the transmitted
energy reflected (or backscattered). (C).
 By measuring time delay distance from the radar
and thus their location can be determined.
 Typical imaging RADAR may give about 1500
high-power pulses per second

45. Application of radar
• Flood mapping,
• Snow mapping,
• Crop classification,
• Forest biomass / timber estimation
• Tree height
• Soil moisture mapping,
• Soil roughness mapping / monitoring
• Crop yield,
• Flood prediction
• Landslide prediction