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1. INTRODUCTION

LIDAR (Light Detection and Ranging) is an optical remote sensing technology that measures properties

scattered light to find range and/or other information of a distant target. The prevalent method to determin

distance to an object or surface is to use laserpulses. Like the similar radar technology, which uses radio wave

the range to an object is determined by measuring the time delay between transmission of a pulse and detection o

the reflected signal. LIDAR technology has application geometrics, archaeology, geograph

y, geology, geomorphology, seismology, forestry, remote sensing and atmospheric physics.[1] Applications

LIDAR include ALSM (Airborne Laser Swath Mapping), laser altimetry or LIDAR Contour Mapping. Th

acronym LADAR (Laser Detection and Ranging) is often used in military contexts. The term laser radar is also i

use but is misleading because it uses laser light and not the radiowaves that are the basis of conventional radar.

1.1GENERAL DESCRIPTION

The primary difference between LIDAR and RADAR is LIDAR uses much shorterwavelengths

the electromagnetic spectrum, typically in the ultraviolet, visible, ornear infrared range. In general it is possible

image a feature or object only about the same size as the wavelength, or larger. Thus LIDAR is highly sensitiv

to aerosols and cloud particles and has many applications in atmospheric research and meteorology.

An object needs to produce a dielectricdiscontinuity to reflect the transmitted wave. At rad

(microwave orradio) frequencies, a metallic object produces a significant reflection. However non-metall

objects, such as rain and rocks produce weaker reflections and some materials may produce no detectab

reflection at all, meaning some objects or features are effectively invisible at radar frequencies. This is especial

true for very small objects (such as single molecules and aerosols).

Lasers provide one solution to these problems. The beam densities and coherency are excellent. Moreov

the wavelengths are much smaller than can be achieved with radio systems, and range from abo

10 micrometers to the UV (ca. 250 nm). At such wavelengths, the waves are "reflected" very well from sma

objects. This type of reflection is calledbackscattering. Different types of scattering are used for different LIDA

applications, most common are Rayleigh scattering, Mie scattering and Raman scattering as well as fluorescenc

Based on different kinds of backscattering, the LIDAR can be accordingly called Rayleigh LIDAR, Mie LIDAR

Raman LIDAR and Na/Fe/K Fluorescence LIDAR and so on. The wavelengths are ideal for makin

measurements of smoke and other airborne particles (aerosols), clouds, and air molecules.

A laser typically has a very narrow beam which allows the mapping of physical features with ver

high resolution compared with radar. In addition, many chemical compounds interact more strongly at visib

wavelengths than at microwaves, resulting in a stronger image of these materials. Suitable combinations of lase

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can allow for remote mapping of atmospheric contents by looking for wavelength-dependent changes in th

intensity of the returned signal.

LIDAR has been used extensively for atmospheric research and meteorology. With the deployment of t

GPS in the 1980s precision positioning of aircraft became possible. GPS based surveying technology has mad

airborne surveying and mapping applications possible and practical. Many have been developed, usin

downward-looking LIDAR instruments mounted in aircraft or satellites. A recent example is the NAS

Experimental Advanced Research LIDAR.

A basic LIDAR system involves a laser range finder reflected by a rotating mirror (top). The laser

scanned around the scene being digitized, in one or two dimensions (middle), gathering distance measurements

specified angle intervals (bottom).

In general there are two kinds of LIDAR detection schema: "incoherent" or direct energy detection (whic

is principally an amplitude measurement) and Coherent detection (which is best for Doppler, or phase sensiti

measurements). Coherent systems generally use Optical heterodyne detection which being more sensitive th

direct detection allows them to operate a much lower power but at the expense of more complex transceiv

requirements.

In both coherent and incoherent LIDAR, there are two types of pulse models: MICROPULS

LIDAR systems and high energy systems. Micropulse systems have developed as a result of the ever increasin

amount ofcomputerpower available combined with advances in laser technology. They use considerably le

energy in the laser, typically on the order of one microjoule, and are often "eye-safe," meaning they can be us

without safety precautions. High-power systems are common in atmospheric research, where they are widely us

for measuring many atmospheric parameters: the height, layering and densities of clouds, cloud particle properti

(extinction coefficient, backscatter coefficient, depolarization), temperature, pressure, wind, humidity, trace g

concentration (ozone, methane, nitrous oxide, etc.).

On a functional level, LiDAR is typically defined as the integration of three technologies into a sing

system capable of acquiring data to produce accurate digital elevation models (DEMs). These technologies ar

lasers, the Global Positioning System (GPS), and inertial navigation systems (INS). Combined, they allow th

positioning of the footprint of a laser beam as it hits an object, to a high degree of accuracy.

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Lasers themselves are very accurate in their ranging capabilities, and can provide distances accurate to a fe

centimeters. The accuracy limitations of LiDAR systems are due primarily to the GPS and IMU (Inerti

Measurement Unit) components. As advancements in commercially available GPS and IMUs occur, it

becoming possible to obtain a high degree of accuracy using LiDAR from moving platforms such as aircraft.

LiDAR system combines a single narrow-beam laser with a receiver system. The laser produces an optical pulthat is transmitted, reflected off an object, and returned to the receiver. The receiver accurately measures th

travel time of the pulse from its start to its return. With the pulse travelling at the speed of light, the receive

senses the return pulse before the next pulse is sent out. Since the speed of light is known, the travel time can b

converted to a range measurement. Combining the laser range, laser scan angle, laser position from GPS, an

laser orientation from INS, accurate x, y, z ground coordinates can be calculated for each laser pulse.

Laser emission rates can be anywhere from a few pulses per second to tens of thousands of pulses per se

ond. Thus, large volumes of points are collected. For example, a laser emitting pulses at 10,000 times per secon

will record 600,000 points every minute. Typical raw laser point spacing on the ground ranges from 2 to 4 meter

Some LiDAR systems can record multiple returns from the same pulse. In such systems the beam ma

hit leaves at the top of tree canopy, while part of the beam travels further and may hit more leaves or branche

Some of the beam is then likely to hit the ground and be reflected back, ending up with a set of recorded multip

returns each having an x, y, z position. This feature can be advantageous when the application calls f

elevations for not only the ground, but for tree or building heights.

As surface types and characteristics vary and change the laser beams reflectivity, then the ability of th

LiDAR to record the return signals changes. For example, a laser used for topographic applications will n

penetrate water, and in fact records very little data even for the surface of the body of water. Where the appl

cation calls for a laser to penetrate water to determine x, y, z positions of undersea features, then a slight

different variation of LiDAR technology is used.

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1.2HYDROGRAPHIC LIDAR VS. TOPOGRAPHIC LIDAR

Airborne LiDAR Hydrography (ALH) has been under development since the mid

1960s. There are currently half a dozen ALH systems in operation, and one of the most

advanced and reliable is the Scanning Hydrographic Operational Airborne LiDAR

Survey, or SHOALS system. It has been described as one of the most versatile

hydrographic LiDAR systems in use in the world today. To the authors knowledge

there is only one SHOALS system in operation, and it is owned by the United States

Army Corps of Engineers.

There are several fundamental differences between a SHOALS system and a

topographic LiDAR system. The principle difference is that the SHOALS system uses

two varying laser beams whereas most topographic systems use a single beam. In

addition, the wavelengths of the laser in each are different. Most topographic LiDAR

uses near infrared beams that reflect off most objects. The SHOALS system uses a red

wavelength (infrared) beam that is reflected by the water surface and detected by the

receiver, as well as a blue-green wavelength beam which penetrates the water surface

and is reflected from the bottom. As shown in the graphic on the left, a hydrographic

LiDAR fires co-aligned laser pulses of the two different wavelengths at the water. The

time difference between the two signals determines the water depth. Another major

difference between a topographic and SHOALS system is the frequency of the emitted

laser beam. Whereas a topographic LiDAR emits beams at up to 30,000 Hz, the

SHOALS system operates at relatively low frequency, emitting pulses at 400 Hz.

A final interesting difference between the SHOALS LiDAR and a typical

topographic LiDAR is the disparate energy requirements of each. Whereas a

topographic system can be used in a relatively small aircraft or helicopter, the SHOALS

system requires much more power to operate. This is due to the power required to

energize a laser beam such that it can penetrate the water to the depths necessary to

map the ocean floor.

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1.3 COMPONENTS

There are several major components to a LIDAR system:

1. Laser 600-1000 nm lasers are most common for non-scientific applications.

They are inexpensive but since they can be focused and easily absorbed by the

eye the maximum power is limited by the need to make them eye-safe. Eye-

safety is often a requirement for most applications. A common alternative

1550 nm lasers are eye-safe at much higher power levels since this wavelength

is not focused by the eye, but the detector technology is less advanced and so

these wavelengths are generally used at longer ranges and lower accuracies.

They are also used for military applications as 1550 nm is not visible in night

vision goggles unlike the shorter 1000 nm infrared laser. Airborne topographic

mapping LIDARS generally use 1064 nm diode pumped YAG lasers, while

bathymetric systems generally use 532 nm frequency doubled diode pumped

YAG lasers because 532 nm penetrates water with much less attenuation than

does 1064 nm. Laser settings include the laser repetition rate (which controls the

data collection speed). Pulse length is generally an attribute of the laser cavity

length, the number of passes required through the gain material (YAG, YLF,

etc.), and Q-switch speed. Better target resolution is achieved with shorterpulses, provided the LIDAR receiver detectors and electronics have sufficient

bandwidth.

2. Scanner and optics How fast images can be developed is also affected by the

speed at which it can be scanned into the system. There are several options to

scan the azimuth and elevation, including dual oscillating plane mirrors, a

combination with a polygon mirror, a dual axis scanner. Optic choices affect the

angular resolution and range that can be detected. A hole mirror or a beam

splitterare options to collect a return signal.

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3. Photodetector and receiver electronics two main photodetector technologies

are used in lidars: solid state photodetectors, such as silicon avalanche

photodiodes, or photomultipliers. The sensitivity of the receiver is another

parameter that has to be balanced in a LIDAR design.

4. Position and navigation systems LIDAR sensors that are mounted on mobile

platforms such as airplanes or satellites require instrumentation to determine the

absolute position and orientation of the sensor. Such devices generally include

a Global Positioning System receiver and an Inertial Measurement Unit (IMU).

1.4 APPLICATIONS

Fig1:LIDAR System

This LIDAR-equipped mobile robot uses its LIDAR to construct a map and avoid

obstacles.

Other than those applications listed above, there are a wide variety of applications of

LIDAR, as often mentioned in Dataset programs.

ARCHAEOLOGY

LIDAR has many applications in the field of archaeology including aiding in the

planning of field campaigns, mapping features beneath forest canopy, and providing an

overview of broad, continuous features that may be indistinguishable on the ground.

LIDAR can also provide archaeologists with the ability to create high-resolution digital

elevation models (DEMs) of archaeological sites that can reveal micro-topography that

are otherwise hidden by vegetation. LIDAR-derived products can be easily integrated

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of the gas as a function of range. DIAL LIDARs are essentially dual-wavelength elastic

backscatter LIDARS.

Raman LIDAR is also used for measuring the concentration of atmospheric

gases, but can also be used to retrieve aerosol parameters as well. Raman LIDAR

exploits inelastic scattering to single out the gas of interest from all other atmospheric

constituents. A small portion of the energy of the transmitted light is deposited in the

gas during the scattering process, which shifts the scattered light to a longer wavelength

by an amount that is unique to the species of interest. The higher the concentration of

the gas, the stronger the magnitude of the backscattered signal.

Doppler LIDAR is used to measure wind speed along the beam by measuring

the frequency shift of the backscattered light. Scanning LIDARs, such as NASA's

HARLIE LIDAR, have been used to measure atmospheric wind velocity in a large

three dimensional cone. ESA's wind mission ADM-Aeolus will be equipped with a

Doppler LIDAR system in order to provide global measurements of vertical wind

profiles. A Doppler LIDAR system was used in the 2008 Summer Olympics to measure

wind fields during the yacht competition.[6] Doppler LIDAR systems are also now

beginning to be successfully applied in the renewable energy sector to acquire wind

speed, turbulence, wind veer and wind shear data. Bothpulsed and continuous wave

systems are being used. Pulsed systems using signal timing to obtain vertical distance

resolution, whereas continuous wave systems rely on detector focusing.

GEOLOGY

In geology and seismology a combination of aircraft-based LIDAR and GPS have

evolved into an important tool for detecting faults and measuring uplift. The output of

the two technologies can produce extremely accurate elevation models for terrain that

can even measure ground elevation through trees. This combination was used most

famously to find the location of the Seattle in Washington, USA.[8] This combination

is also being used to measure uplift at Mt. St. Helens by using data from before and

after the 2004 uplift.[9] Airborne LIDAR systems monitorglaciers and have the ability

to detect subtle amounts of growth or decline. A satellite based system

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isNASA's ICESat which includes a LIDAR system for this purpose. NASA's Airborne

Topographic Mapper is also used extensively to monitorglaciers and perform coastal

change analysis.

PHYSICS AND ASTRONOMY

A worldwide network of observatories uses lidars to measure the distance to reflectors

placed on the moon, allowing the moon's position to be measured with mm precision

and tests of general relativity to be done. MOLA, the Mars Orbiting Laser Altimeter,

used a LIDAR instrument in a Mars-orbiting satellite (the NASA Mars Global

Surveyor) to produce a spectacularly precise global topographic survey of the red

planet.

In September, 2008, NASA's Phoenix Landerused LIDAR to detect snow in the

atmosphere of Mars.

In atmospheric physics, LIDAR is used as a remote detection instrument to

measure densities of certain constituents of the middle and upper atmosphere, such

aspotassium, sodium, or molecularnitrogen and oxygen. These measurements can be

used to calculate temperatures. LIDAR can also be used to measure wind speed and to

provide information about vertical distribution of the aerosol particles.

BIOLOGY AND CONSERVATION

LIDAR has also found many applications

in forestry. Canopy heights,biomass measurements, and leaf area can all be studied

using airborne LIDAR systems. Similarly, LIDAR is also used by many industries,

including Energy and Railroad, and the Department of Transportation as a faster way of

surveying. Topographic maps can also be generated readily from LIDAR, including for

recreational use such as in the production oforienteering maps.

In oceanography, LIDAR is used for estimation

ofphytoplankton fluorescence and generally biomass in the surface layers of the ocean.

Another application is airborne LIDAR bathymetry of sea areas too shallow

forhydrographic vessels.

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In addition, the Save-the-Redwoods League is undertaking a project to map the

tall redwoods on California's northern coast. LIDAR allows research scientists to not

only measure the height of previously unmapped trees but to determine the biodiversity

of the redwood forest. Stephen Sillett who is working with the League on the North

Coast LIDAR project claims this technology will be useful in directing future efforts to

preserve and protect ancient redwood trees.

MILITARY AND LAW ENFORCEMENT

One situation where LIDAR has notable non-scientific application is in traffic

speed enforcement, for vehicle speed measurement, as a technology alternative to radar

guns. The technology for this application is small enough to be mounted in a hand held

camera "gun" and permits a particular vehicle's speed to be determined from a stream

of traffic. Unlike RADAR which relies on Doppler shifts to directly measure speed,

police LIDAR relies on the principle of time-of-flight to calculate speed. The

equivalent radar based systems are often not able to isolate particular vehicles from the

traffic stream and are generally too large to be hand held. LIDAR has the distinct

advantage of being able to pick out one vehicle in a cluttered traffic situation as long as

the operator is aware of the limitations imposed by the range and beam divergence.

LIDAR does not suffer from sweep error when the operator uses the

equipment correctly and when the LIDAR unit is equipped with algorithms that are able

to detect when this has occurred. A combination of signal strength monitoring, receive

gate timing, target position prediction and pre-filtering of the received signal

wavelength prevents this from occurring. Should the beam illuminate sections of the

vehicle with different reflectivity or the aspect of the vehicle changes during

measurement that causes the received signal strength to be changed then the LIDAR

unit will reject the measurement thereby producing speed readings of high integrity. ForLIDAR units to be used in law enforcement applications a rigorous approval procedure

is usually completed before deployment. The use of many reflections and an averaging

technique in the speed measurement process increase the integrity of the speed reading.

Vehicles are usually equipped with a vertical registration plate that, when illuminated,

causes a high integrity reflection to be returned to the LIDAR - despite the shape of the

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vehicle. In locations that do not require that a front or rear registration plate is fitted,

headlamps and rear-reflectors provide almost ideal retro-reflective surfaces overcoming

the reflections from uneven or non-compliant reflective surfaces thereby eliminating

sweep error. It is these mechanisms which cause concern that LIDAR is somehow

unreliable.

Most traffic LIDAR systems send out a stream of approximately 100 pulses

over the span of three-tenths of a second. A "black box" proprietary statistical algorithm

picks and chooses which progressively shorter reflections to retain from the pulses over

the short fraction of a second.

Military applications are not yet known to be in place and are possibly

classified, but a considerable amount of research is underway in their use for imaging.

Higher resolution systems collect enough detail to identify targets, such as tanks. Here

the name LADAR is more common.

Utilizing LIDAR and THz interferometer wide area raman spectroscopy, it is

possible to detect chemical, nuclear, or biological threats at a great distance. Further

investigations regarding long distance and wide area spectroscopy are currently

conducted by Sandia National Laboratories.

Five LIDAR units produced by the German company Sick AG were used for

short range detection on Stanley, the autonomous carthat won the 2005 DARPA Grand

Challenge.

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VEHICLES

LIDAR has been used in Adaptive Cruise Control (ACC) systems for automobiles.

Systems such as those by Siemens and Hella use a LIDAR device mounted on the front

of the vehicle, such as the bumper, to monitor the distance between the vehicle and any

vehicle in front of it. In the event the vehicle in front slows down or is too close, the

ACC applies the brakes to slow the vehicle. When the road ahead is clear, the ACC

allows the vehicle to accelerate to a speed preset by the driver.

IMAGING

3-D imaging is done with both scanning and non-scanning systems. "3-D gated viewing

laser radar" is a non-scanning laser radar system that applies the so-called gated

viewing technique. The gated viewing technique applies a pulsed laser and a fast gated

camera. There are ongoing military research programmes in Sweden, Denmark, the

USA and the UKwith 3-D gated viewing imaging at several kilometers range with a

range resolution and accuracy better than ten centimeters.

Coherent Imaging LIDAR is possible using Synthetic array heterodyne

detection which is a form ofOptical heterodyne detection that enables a staring single

element receiver to act as though it were an imaging array. This avoids the need for a

gated camera and all ranges from all pixels are simultaneously available in the image.

Imaging LIDAR can also be performed using arrays of high speed detectors and

modulation sensitive detectors arrays typically built on single chips using CMOS and

hybrid CMOS/CCD fabrication techniques. In these devices each pixel performs some

local processing such as demodulation or gating at high speed down converting the

signals to video rate so that the array may be read like a camera. Using this technique

many thousands of pixels / channels may be acquired simultaneously. In practicalsystems the limitation is light budget rather than parallel acquisition.

LIDAR has been used in the recording of a music video without cameras. The

video for the song "House of Cards" by Radiohead is believed to be the first use of real-

time 3D laser scanning to record a music video.

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http://en.wikipedia.org/wiki/Adaptive_Cruise_Controlhttp://en.wikipedia.org/wiki/Swedenhttp://en.wikipedia.org/wiki/Denmarkhttp://en.wikipedia.org/wiki/United_Kingdomhttp://en.wikipedia.org/wiki/Synthetic_array_heterodyne_detectionhttp://en.wikipedia.org/wiki/Synthetic_array_heterodyne_detectionhttp://en.wikipedia.org/wiki/Optical_heterodyne_detectionhttp://en.wikipedia.org/wiki/House_of_Cards_(song)http://en.wikipedia.org/wiki/Radioheadhttp://en.wikipedia.org/wiki/Adaptive_Cruise_Controlhttp://en.wikipedia.org/wiki/Swedenhttp://en.wikipedia.org/wiki/Denmarkhttp://en.wikipedia.org/wiki/United_Kingdomhttp://en.wikipedia.org/wiki/Synthetic_array_heterodyne_detectionhttp://en.wikipedia.org/wiki/Synthetic_array_heterodyne_detectionhttp://en.wikipedia.org/wiki/Optical_heterodyne_detectionhttp://en.wikipedia.org/wiki/House_of_Cards_(song)http://en.wikipedia.org/wiki/Radiohead

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2. LIDAR DATA

What can you do with LIDAR?

Measure distance

Measure speed

Measure rotation

Measure chemical composition and concentration

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Fig 2: Comparison of various steps involved in DTM generation, Photogrammetry vs.

LIDAR

2.1WHAT ARE LIDAR DATA?

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Light Detection and Ranging (LIDAR) is a remo

sensing system used to collect topographic data. Th

technology is being used by the National Ocean

and Atmospheric Administration (NOAA) an

NASA scientists to document topographic chang

along shorelines. These data are collected wi

aircraft-mounted lasers capable of recordi

elevation measurements at a rate of 2,000 to 5,00

pulses per second and have a vertical precision of

centimeters (6 inches). After a baseline data set h

been created, follow-up flights can be used to dete

shoreline changes.

Fig 3:LIDAR DATA

2.2 HOW LIDAR DATA ARE COLLECTED

For the South Carolina project, a LIDAR sensor was mounted on-board a NOAA

DeHavilland Twin Otter aircraft pictured below. Once in flight, the aircraft travels over

the beach at approximately 60 meters per second. During the flight, the LIDAR sensor

pulses a narrow, high frequency laser beam toward the earth through a port opening in

the bottom of the aircraft's fuselage. The LIDAR sensor records the time difference

between the emission of the laser beam and the return of the reflected laser signal to the

aircraft.

The LIDAR transceiver is rigidly fastened to the aircraft and does not move. However,

a scan mirror assembly is mounted beneath the transceiver. A 45-degree folding mirror

reflects the laser pulses onto a moving mirror which directs the laser pulses to the earth.

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The reflected laser light from the ground follows the reverse optical path and is

directed into a small Cassegrainian telescope. The moving mirror produces a conical

sampling pattern beneath the aircraft over a 30-degree wide swath, thus permitting the

collection of topographic information over a strip approximately 300 meters (about

1000 feet) in width from the nominal 600 meter (2000 feet) data collection altitude.

Fig 4:Illustration of How the LIDAR Sensing Instrument Captures Elevation

Points.

The LIDAR instruments only collect elevation data. To make these data

spatially relevant, the positions of the data points must be known. A high-precision

global positioning system (GPS) antenna is mounted on the upper aircraft fuselage. As

the LIDAR sensor collects data points, the location of the data are simultaneously

recorded by the GPS sensor. After the flight, the data are downloaded and processed

using specially designed computer software. The end product is accurate,

geographically registered longitude, latitude, and elevation (x, y, z) positions for every

data point. These "x, y, z" data points allow the generation of a digital elevation model(DEM) of the ground surface.

LIDAR data sets on this CD-ROM cover an area from the low water line to the

landward base of the sand dunes. Flights are planned to maximize the number of

elevation points collected at the lowest tide for the largest area possible. The aircraft

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flight path is always parallel to the beach. Four passes are flown over each section of

the beach. Two of these passes are flown so the center of the swath is over the

sand/water interface. The other two passes are flown over the center of the

sand/development interface.

Flights generally last four hours. Weather conditions must be monitored. The

flights cannot be flown during times of rain or fog as the water vapor in the air could

cause the laser beams to scatter and give a false reading. Additionally, the plane cannot

fly during times of high winds as the returned laser pulse will not be recorded correctly.

2.3 INTERPRETING LIDAR ELEVATION MAPS

In remote sensing, false color images such as LIDAR elevation maps are common.

They serve as an effective means for visualizing data. The term "false color" refers to

the fact that these images are not photographs. Rather, they are digital images in which

each image pixel represents a data point that is colored according to its value. The

purpose of this section is to aid users in interpreting false color images.

LIDAR beach mapping data are composed of elevation measurements of the

beach surface and are acquired through aerial topographic surveys. The file format used

to capture and store LIDAR data is a simple text file and referred to as "x,y,z," where x

is longitude, y is latitude, and z is elevation. Using the elevation "points," LIDAR data

may be used to create detailed topographic beach maps.

In the three images shown below, the legend in the bottom right corner of the

image has a range of numbers from -3 meters to +5 meters. The numbers indicate the

relationship between the colors on the legend and the elevations depicted on the map.

For example, in the Huntington Beach map, the deep blue color represents land

approximately at sea level or zero elevation. The cyan (light blue) features, like the

jetty, represent elevations around 1 meter, or about 3 feet above sea level.

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Fig 5:LIDAR DATA

LIDAR data become easier to interpret when examined in conjunction with additional

data such as aerial photography. In the example below a LIDAR elevation map is

compared with an orthophotograph. This small area on Kiawah Island provides avariety of interesting features. Comparing the orthophoto to the LIDAR data it becomes

easier to identify features such as houses, roads, the vegetated dune area, and irrigation

ponds.

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Fig 6:Comparing Features Found in an Orthophotograph to LIDAR Data

Along the South Carolina coast, beach features tend to be less than 5 meters (16 feet).

As a result, the scale of the color bar was chosen to highlight relatively narrow

variations in elevation. This legend can be readily viewed in the PDF maps located in

the pdf/islands directory on this CD-ROM. Additionally, this legend has been provided

for use in Arc View and is located at: data/LIDAR/avelev.shp.

In this second example, an additional vector base map was overlaid on both the

orthophoto and LIDAR elevation map. The base map, created in 1993, includes

digitized building footprints, dune walkovers, and roads. A detailed base map can assist

in confirming features detected by LIDAR elevation measurements. For example, when

houses are surrounded by tall vegetation, LIDAR elevation data do not distinguish

between roof top and tree top. Without the vector base map, it would be very difficult

to determine boundaries between roofs and trees. Often ancillary data do not provide

sufficient detail or are not available. In these cases, the user must obtain ground

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3.1 FLOOD RISK MAPPING

LiDAR surveys are one of the quickest and most accurate methods to produce a DEM.

Using the LiDAR derived DEM, hydrologists are able to predict flood extents and plan

mitigation and remediation strategies. The reliability of flood risk mapping and

hydrological models is dependent on the accuracy of the terrain elevation data used.

This is especially true for modeling in areas of little terrain relief. For example, in a flat

river basin such as the Red River in Manitoba and North Dakota, a slight increase in

water level can flood a large area. This may mean that many communities would be

affected by a rise in water level. In areas with more relief, the accuracy of the DEM is

not as critical, but knowledge of slope and aspect can aid considerably in predicting

water volumes and flow characteristics.

The following is an excerpt from the IJCs final report Living with the Red,

and is based on the results of LiDAR surveys done in the region:

The Task Force found that current mapping of high risk areas was not adequate

for modeling and analysis of flood risk, or for the consideration of flood protection

options. Among other things, the Task Force produced high-resolution digital elevation

data for the lower Pembina River and for the area south of the Winnipeg Floodway, and

analyzed data collection technologies. Through these efforts, the Task Force found that

airborne laser mapping can be a fast, reliable, and cost-effective method of obtaining

three-dimensional data suitable for the creation of a digital elevation models (DEM).

3.2 OIL & GAS EXPLORATION SURVEYS

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The oil and gas industry relies upon rapid delivery of time sensitive data relating the X,

Y and Z positions of terrain data for exploration programs. Although this critical

positional data can be collected by alternate means, LiDAR surveys provide high-speed

data acquisition and limit ground intervention. In many instances, the time from field

survey to final data product delivery can be accomplished within a few weeks, not

months. In environmentally sensitive areas, tree-cutting fees can amount to thousands

of dollars per hectare. Using LiDAR as the survey tool, fewer lines need to be cut,

fewer trees are felled, and the exploration companies realize significant savings.

Typically, surveys for the oil and gas industry are conducted using either a

fixed-wing or helicopter mounted LiDAR system, based on the size, terrain, and

vegetation coverage of the project area.

3.3 ENGINEERING/CONSTRUCTION SURVEYS

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LiDAR surveys are well suited for producing accurate elevation data for engineering

surveys of road and other construction projects. Using DEMs created from LiDAR, cut

and fill quantities can be more precisely estimated during planning stages when

compared to ground survey or photogrammetric techniques. The DEM can also be used

in conjunction with GIS and CAD software to enable planners and engineers to model

various scenarios in choosing the best route or location for future construction.

As-built surveys can be used as a stand-alone record of construction, or as a

comparison with the pre-construction survey to validate initial quantity estimates.

Combining a LiDAR DEM with orthophotos can provide an engineering design team

with all the topographic and planimetric information they need.

Using LiDAR survey technology, the time between data acquisition and

delivery of the finished DEM/Orthophoto product to the client can be far shorter than

any other survey methodology, an important consideration for time sensitive projects.

3.4 REAL ESTATE DEVELOPMENT

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Traditional ground surveying for real-estate development purposes is a time consuming

and labor intensive task because of the accuracy and precision requirement of the DEM.

Airborne LiDAR surveys offer real estate developers a cost-effective way to quickly

obtain precise topographic and elevation data in urban, suburban, and rural areas with

minimal human presence on the ground. Developers frequently require a DEM accurate

to within 15 cm, thereby enabling them to optimize lot design, as well as excavation

and fill requirements. Adding high-resolution digital orthophoto provides developers,

town planners, engineers, and contractors with all the digital data needed to plan new

infrastructure and development projects. A recent LiDAR project was conducted for a

land developer on Vancouver Island that included the derivation of a DEM along with

orthophoto for mapping and planning purposes.

3.5 TRASMISSION LINE MAPPING

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LiDAR technology lends itself particularly well to transmission line surveys, especially

if the data acquisition system is mounted in a helicopter. Using a helicopter for corridor

mapping can be much more cost-effective than a fixed-wing, since the helicopter can

follow the corridors path easily, staying directly over the power line or pipeline at all

times.

A helicopter system can also ensure that a rigorous data set is acquired, since

flight speed and altitude can be adjusted as necessary during flight. With the addition of

a digital still camera, a video camera, or other sensors to the helicopter pod, inventory

mapping and line inspection can be undertaken at the same time as the LiDAR survey.

LiDAR and image data can be used for several applications in corridor mapping

including:

Calculating power line heights or sag under different loads

Inventory

Tower Placement

Height of underlying vegetation

Several hydro utilities have conducted LiDAR based data collection projects toevaluate the technology, and now are using the LiDAR data operationally for line re-

rating, tower/line re-engineering and line site selection

3.6 COASTAL ZONE MAPPING

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One of the first areas investigated for commercial application of LiDAR was the forest

industry. Accurate information of the terrain and topography beneath the tree canopy is

extremely important to both foresters and natural resource managers. Accurate

information on tree heights and densities is critical information that is difficult to obtain

using conventional techniques. Airborne laser technology, unlike radar or satellite

imaging, can simultaneously map the ground beneath the tree canopy as well as the tree

heights. Post-processing of the data allows the individual laser returns to be analysed

and classified as vegetation or ground returns, allowing for both a ground DEM and a

tree canopy model. Using application-specific software it is possible to compute

information related to the forest industry such as; tree heights, crown cover and

biomass. Consequently, airborne laser mapping is an extremely effective tool for

forestry companies especially when compared to traditional tools such as

photogrammetry or ground surveys. There is still much work to do in developing

reliable and robust modelling software for the forest industry, and this is an area where

university research is playing a role.

3.8 URBAN MODELLING.

Accurate digital models of urban environments are required for a variety of applications

including telecommunications, wireless communications, law enforcement and disaster

planning. Using the proper operational parameters, LiDAR offers the ability to

accurately map urban environments without shadowing. Detailed Surface Elevation

Models (SEMs) can be extracted from the LiDAR data, and enhanced for applied

analysis using specialized 3-D rendering software.

3.9 WETLANDS AND OTHER RESTRICTED ACCESS AREAS

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Many environmentally sensitive areas such as wetlands, wildlife reserves, and protected

forest areas are difficult to map using conventional ground or photogrammetric

techniques. This is due to often dense vegetation cover and limited access roads, which

make it difficult to access for ground surveys, and inherently difficult to map using

traditional photogrammetry. Airborne LiDAR mapping offers the capability to survey

these areas. The technology can also be deployed to survey toxic waste sites or

industrial waste dumps.

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3.10 OTHER APPLICATIONS

Miscellaneous other applications of LiDAR include the following:

Property assessment, where county-wide mapping programs are being supported

Airport Exclusion zones, where landing and takeoff zones are mapped with

LiDAR

height restrictions;

Rectification of Satellite Imagery, where LiDAR is used to provide the DEM to

complete the satellite image rectification process.

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4. SHOALS-SPECIFIC APPLICATIONS

While most of the preceding applications have been directed at topographic LiDARsystems, there are several key applications that can only be conducted with a

hydrographic LiDAR.

4.1 UNDERSEA CABLE ROUTING:

With more and more cables being placed underwater, the demand for precise

information of the seafloor structure is increasing. Although not applicable in a deep-

water situation, a hydrographic LiDAR can provide data to ascertain the best possible

routing for a subsurface cable in water depths of up to 50 meters. Given that the

shallower waters in the near shore regions are likely the most populated with

underwater furniture, a LiDAR system may be the only way to gather the data

required. Additionally, it has been documented that other underwater sensors such as

Multi Beam Sonar (MBS) are difficult to operate and are less reliable in shallower

waters.

4.2 WRECK DETECTION:

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Several projects have been conducted using LiDAR to detect underwater shipwrecks,

especially in shallower waters. With the ability of LiDAR to operate in these depths of

water, and given the accuracy of the system, it has been shown that the technology is a

viable way to detect and identify sunken ships.

4.3 CHARTING & SAFETY ISSUES:

Electronic Charts are replacing paper maps for navigation at sea, in harbors and in

ports. Various data is required to compile the charts, and hydrographic LiDAR is

capable of providing data to support their generation. Combined with soundings, multi

beam sonar and other data, the LiDAR component adds extreme value to the end result.

One initiative being spearheaded by the Canadian Hydrographic Service is the concept

of a seamless chart that encompasses the sea and the land. With the increasing

versatility of LiDAR technology, these charts will become a reality.

5. CONCLUSIONS:

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LiDAR mapping is a maturing technology, and applications are still being identified

and developed as end-users begin to work with the data. There are on-going initiatives

to identify areas where the technology allows value-added products to be generated or

where it offers significant cost reductions over traditional survey methods.

There are a number of conclusions to be drawn from the information presented

herein. These deal with LiDAR technology itself, the impact of the technology on the

survey and mapping industry, and the societal and economic benefits that accrue

through its use. They have been presented below in point form, in no particular order.

1. LiDAR is an enabling technology. Primarily, it has allowed data to be collected

that was difficult or impossible to obtain prior to its introduction. This is

especially true in the forest industry and utility corridor arena, where it has been

very difficult and expensive to get elevation models using ground-based GPS,

conventional survey and/or photogram metric techniques.

2. LiDAR is an enhancing technology. For applications where a more precise

DEM is required, such as engineering and road design and flood plain mapping,

LiDAR is able to provide much more information than can be acquired by

virtually any other means at least within economic reason.

3. LiDAR has revolutionized the survey and mapping world. In practical terms,

hydrographic LiDAR has been a viable survey tool since the early 1980s. With

the advent of a full constellation of GPS in the early 1990s, hydrographic

LiDAR has taken a giant leap forward in being able to provide accurate data for

difficult survey operations. Topographic LiDAR has evolved from a relative

physics experiment to a useable and reliable survey tool, all since the mid

1990s. Now that the technological chasm is virtually crossed, and more

people are buying into LiDAR, the survey and mapping industry is racing to

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meet the demand for services. This includes the industrys ability to properly

acquire, process and quality control the data.

4. LiDAR has empowered clients. The speed with which data can be collected, and

the relative speed at which it can be processed compared to any other

technology, has given clients the power to demand products more quickly. In

many cases, time saved on surveying and mapping translates into huge

downstream economic gains.

5. LiDAR saves clients money. For many projects, especially those where DEMs

are required for heavily vegetated areas, LiDAR can greatly reduce survey time

and effort. This translates directly into cost savings for clients.

6. LiDAR offers flexibility. Although it can be said of data collected via other

methods, data collected by LiDAR is extremely versatile. It can be used for

anything from power line detection to DEM generation in a second growth

forest. This is due to the tremendous point density achieved from LiDAR, its

accuracy, and its ability to penetrate to the ground through foliage in vegetated

areas.

7. LiDAR is unobtrusive and environmentally friendly. Unlike ground survey

techniques, airborne LiDAR can be flown over areas where access is limited,

impossible, or undesirable. Apart from the need to validate the

8. LiDAR with ground truthing, it is not necessary to send pervasive ground crews

to conduct intense survey operations. LiDAR surveying can also avoid

unnecessary tree cutting and other practices that can harm the environment.

In conclusion, it is hoped that this paper will have provided an insight into the

possibilities of LiDAR, and will elicit discussion regarding the use of LiDAR to

conduct mapping projects. Given the versatility of the technology, and its maturation, it

seems logical that any strategic plan or project should at least consider its use. If

required, more information can be obtained by contacting TerraPoint.

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6. REFERENCES

1. Cracknell, Arthur P.; Hayes, Ladson (2007) [1991], Introduction to Remote

Sensing (2 ed.), London: Taylor and

Francis, ISBN0849392551, OCLC70765252

2. ^'Experimental Advanced Research Lidar', NASA.org. Retrieved 8 August

2007.

3. ^EID; crater beneath canopy

4. ^Thomas D. Wilkerson, Geary K. Schwemmer, and Bruce M. Gentry. Lidar

Profiling of Aerosols, Clouds, and Winds by Doppler and Non-Doppler

Methods, NASA International H2O Project (2002).

5. ^'Earth Explorers: ADM-Aeolus', ESA.org (European Space Agency, 6 June

2007). Retrieved 8 August 2007.

6. ^'Doppler lidar gives Olympic sailors the edge', Optics.org (3 July, 2008).

Retrieved 8 July 2008.

7. ^ ab Strauss C. E. M., "Synthetic-array heterodyne detection: a single-element

detector acts as an array", Opt. Lett. 19, 1609-1611 (1994)

8. ^Tom Paulson. 'LIDAR shows where earthquake risks are highest, Seattle

Post (Wednesday, April 18, 2001).

9. ^'Mount Saint Helens Lidar Data', Washington State Geospatial Data

Archive (September 13, 2006). Retrieved 8 August 2007.

10.^'Airborne Topographic Mapper', NASA.gov. Retrieved 8 August 2007.

11.^NASA. 'NASA Mars Lander Sees Falling Snow, Soil Data Suggest Liquid

Past' NASA.gov (29 September 2008). Retrieved 9 November 2008.

12.^CW Gowers. ' Focus On : Lidar-Thomson Scattering Diagnostic on

JET' JET.EFDA.org (undated). Retrieved 8 August 2007.

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http://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/Special:BookSources/0849392551http://en.wikipedia.org/wiki/Online_Computer_Library_Centerhttp://www.worldcat.org/oclc/70765252http://en.wikipedia.org/wiki/LIDAR#cite_ref-1http://inst.wff.nasa.gov/eaarl/http://en.wikipedia.org/wiki/LIDAR#cite_ref-2http://www.unb.ca/passc/ImpactDatabase/images/whitecourt.htmhttp://en.wikipedia.org/wiki/LIDAR#cite_ref-3http://harlie.gsfc.nasa.gov/IHOP2002/Pub&Pats/AMOS%202002%20final.pdfhttp://harlie.gsfc.nasa.gov/IHOP2002/Pub&Pats/AMOS%202002%20final.pdfhttp://harlie.gsfc.nasa.gov/IHOP2002/Pub&Pats/AMOS%202002%20final.pdfhttp://en.wikipedia.org/wiki/LIDAR#cite_ref-4http://www.esa.int/esaLP/ESAES62VMOC_LPadmaeolus_0.htmlhttp://www.esa.int/esaLP/ESAES62VMOC_LPadmaeolus_0.htmlhttp://en.wikipedia.org/wiki/LIDAR#cite_ref-5http://optics.org/cws/article/research/34878http://en.wikipedia.org/wiki/LIDAR#cite_ref-Strauss_6-0http://en.wikipedia.org/wiki/LIDAR#cite_ref-Strauss_6-1http://www.opticsinfobase.org/ol/abstract.cfm?id=12612http://www.opticsinfobase.org/ol/abstract.cfm?id=12612http://en.wikipedia.org/wiki/LIDAR#cite_ref-7http://seattlepi.nwsource.com/local/19144_quake18.shtmlhttp://seattlepi.nwsource.com/local/19144_quake18.shtmlhttp://en.wikipedia.org/wiki/LIDAR#cite_ref-8http://wagda.lib.washington.edu/data/type/elevation/lidar/st_helens/http://wagda.lib.washington.edu/data/type/elevation/lidar/st_helens/http://en.wikipedia.org/wiki/LIDAR#cite_ref-9http://atm.wff.nasa.gov/http://en.wikipedia.org/wiki/LIDAR#cite_ref-10http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080929.htmlhttp://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080929.htmlhttp://en.wikipedia.org/wiki/LIDAR#cite_ref-11http://www.jet.efda.org/pages/focus/lidar/index.htmlhttp://www.jet.efda.org/pages/focus/lidar/index.htmlhttp://en.wikipedia.org/wiki/International_Standard_Book_Numberhttp://en.wikipedia.org/wiki/Special:BookSources/0849392551http://en.wikipedia.org/wiki/Online_Computer_Library_Centerhttp://www.worldcat.org/oclc/70765252http://en.wikipedia.org/wiki/LIDAR#cite_ref-1http://inst.wff.nasa.gov/eaarl/http://en.wikipedia.org/wiki/LIDAR#cite_ref-2http://www.unb.ca/passc/ImpactDatabase/images/whitecourt.htmhttp://en.wikipedia.org/wiki/LIDAR#cite_ref-3http://harlie.gsfc.nasa.gov/IHOP2002/Pub&Pats/AMOS%202002%20final.pdfhttp://harlie.gsfc.nasa.gov/IHOP2002/Pub&Pats/AMOS%202002%20final.pdfhttp://harlie.gsfc.nasa.gov/IHOP2002/Pub&Pats/AMOS%202002%20final.pdfhttp://en.wikipedia.org/wiki/LIDAR#cite_ref-4http://www.esa.int/esaLP/ESAES62VMOC_LPadmaeolus_0.htmlhttp://www.esa.int/esaLP/ESAES62VMOC_LPadmaeolus_0.htmlhttp://en.wikipedia.org/wiki/LIDAR#cite_ref-5http://optics.org/cws/article/research/34878http://en.wikipedia.org/wiki/LIDAR#cite_ref-Strauss_6-0http://en.wikipedia.org/wiki/LIDAR#cite_ref-Strauss_6-1http://www.opticsinfobase.org/ol/abstract.cfm?id=12612http://www.opticsinfobase.org/ol/abstract.cfm?id=12612http://en.wikipedia.org/wiki/LIDAR#cite_ref-7http://seattlepi.nwsource.com/local/19144_quake18.shtmlhttp://seattlepi.nwsource.com/local/19144_quake18.shtmlhttp://en.wikipedia.org/wiki/LIDAR#cite_ref-8http://wagda.lib.washington.edu/data/type/elevation/lidar/st_helens/http://wagda.lib.washington.edu/data/type/elevation/lidar/st_helens/http://en.wikipedia.org/wiki/LIDAR#cite_ref-9http://atm.wff.nasa.gov/http://en.wikipedia.org/wiki/LIDAR#cite_ref-10http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080929.htmlhttp://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080929.htmlhttp://en.wikipedia.org/wiki/LIDAR#cite_ref-11http://www.jet.efda.org/pages/focus/lidar/index.htmlhttp://www.jet.efda.org/pages/focus/lidar/index.html

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LIST OF FIGURE

Fig1: Lidar System

Fig 2: Comparison of Various Steps Involved In Dtm Generation, Photogrammetric Vs.

Lidar

Fig 3: Lidar Data

Fig 4: Illustration Of How The Lidar Sensing Instrument Captures Elevation Points.

Fig 5: Lidar Data

Fig 6: Comparing Features Found In an Orthophotograph to Lidar Data

Fig7: Example of How Vector Data Can Be Useful In Identifying Features In Lidar

Data

Fig 8: Lidar Data Viewed As a Profile