Airborne Laser Scanning and its Airborne Laser Scanning and its Applications Applications

Prof.Dr.S.AnbazhaganProf.Dr.S.Anbazhagan

Centre for Geoinformatics & Planetary StudiesCentre for Geoinformatics & Planetary Studies

Department of GeologyDepartment of Geology

Periyar UniversityPeriyar University

SalemSalem

About Airborne Laser ScanningAbout Airborne Laser Scanning Case study in parts of Elbe river basinCase study in parts of Elbe river basin Selected applicationsSelected applications

Airborne laser scanning (ALS) represents a new and Airborne laser scanning (ALS) represents a new and independent technology for the generation of highly independent technology for the generation of highly automated digital terrain and surface models. automated digital terrain and surface models.

ALS development goes back to the 1970’s and 1980’s, ALS development goes back to the 1970’s and 1980’s, with an early NASA system and other attempts in USA and Canadawith an early NASA system and other attempts in USA and Canada

The acronym ‘The acronym ‘LASER’LASER’ stands for ‘ stands for ‘Light Amplification by Light Amplification by Simulated Emission of Radiation’Simulated Emission of Radiation’

LADARLADAR – LAser Detection And Ranging – LAser Detection And Ranging

LIDARLIDAR – Light Detection And Ranging – Light Detection And RangingALS is member of the LIDAR familyALS is member of the LIDAR familyLIDAR includes terrestrial laser scanners, airborne laser LIDAR includes terrestrial laser scanners, airborne laser Scanners and even police speed detection equipmentScanners and even police speed detection equipment

What is Airborne Laser scanning?

ALS data and AccuracyALS data and Accuracy

Laser scanning systems furnish geometric results in terms of Laser scanning systems furnish geometric results in terms of

distance, position, altitude and coordinatesdistance, position, altitude and coordinates

Measuring rates 2KHz to 25KHz, go up to 80KHzMeasuring rates 2KHz to 25KHz, go up to 80KHz

Sampling densitySampling density on the ground range from about 1 point / 20 on the ground range from about 1 point / 20

Sqm area up to 20 points per sq m area.Sqm area up to 20 points per sq m area.

Vertical accuracyVertical accuracy -0.15m & point spacing 1.5m with an -0.15m & point spacing 1.5m with an

accuracy of 0.15 maccuracy of 0.15 m

Airborne Laser Scanning (ALS) – Airborne Laser Scanning (ALS) – Active SensingActive Sensing

Efficient tool for generating accurate DTMs Efficient tool for generating accurate DTMs day day or nightor night, especially over large areas of , especially over large areas of featureless or densely covered terrain.featureless or densely covered terrain.

All laser systems measure by some means the All laser systems measure by some means the distance between the sensor and the distance between the sensor and the illuminated spot on groundilluminated spot on ground

Control monitoringand recording units

Ranging Unit Scanner

DGPS IMUSwath Width

Flight direction

Laser Footprint

A Typical ALS System

Components in ALS systemComponents in ALS system

A dual frequency A dual frequency GPS receiverGPS receiver mounted in mounted in the aircraft, the aircraft, positions the ALS unitpositions the ALS unit, typically , typically every 0.5 secondsevery 0.5 seconds

An An Inertial Measuring UnitInertial Measuring Unit (IMU)(IMU) records records orientation of the aircraftorientation of the aircraft, 200 times/sec , 200 times/sec

Laser distance measurement unitLaser distance measurement unit emits up to emits up to 50,000 discrete light beams/sec, records the 50,000 discrete light beams/sec, records the travel time and calculates the distance to the travel time and calculates the distance to the groundground

Laser rangingLaser ranging

Two ranging principles;Two ranging principles;

The The pulsed ranging principlepulsed ranging principle involves by measuring involves by measuring the phase difference between the the phase difference between the transmitted transmitted and and the the received signalreceived signal back scattered from the object back scattered from the object surface. surface.

The The phase difference methodphase difference method applied with lasers applied with lasers that continuously emit light are called ‘that continuously emit light are called ‘continuous continuous wave’ (CW) lasers. wave’ (CW) lasers.

Time-of-flight ranging

Receiver

Transmitter

R

tL

AT

AR

Traveling Time

Transmitted amplitude

Received amplitude

Range (distance between sensor and object)Range (distance between sensor and object)

R = C t/2R = C t/2

C = velocity of light 300000 km/sC = velocity of light 300000 km/st = traveling time of a light pulset = traveling time of a light pulse

Range resolution ∆R, in cmRange resolution ∆R, in cm

∆∆R = C ∆t/2R = C ∆t/2

∆∆t = ns, resolution of time measurementt = ns, resolution of time measurementt = ns, time between sending and receiving a pulse (or echo)t = ns, time between sending and receiving a pulse (or echo)

1 ns = 30 cm travel, then range = 15 cm 1 ns = 30 cm travel, then range = 15 cm

(Baltsavias 1999)(Baltsavias 1999)

Lasers and Lasers and wavelengthwavelength

At present At present semiconductor diode lasersemiconductor diode laser and Nd: YAG lasers ( and Nd: YAG lasers (neodymium-neodymium-doped yttrium aluminum garnetdoped yttrium aluminum garnet; ; Nd:YNd:Y33AlAl55OO1212 ) ) pumped by pumped by semiconductor lasers are used in the ALS system.semiconductor lasers are used in the ALS system.

It covers optical band range It covers optical band range 800 nm – 1600 nm800 nm – 1600 nm

Most Most sensitive detectorssensitive detectors are available between are available between 800 nm and 1000 nm800 nm and 1000 nm

FFirst scanners were worked irst scanners were worked 900 nm900 nm. At this wavelength, powerful . At this wavelength, powerful pulsed semiconductor laser diodes were available on the market and pulsed semiconductor laser diodes were available on the market and on optimum system performance could be expected. However, at this on optimum system performance could be expected. However, at this wavelength, wavelength, eye safetyeye safety is still concern. is still concern.

The The TopoSysTopoSys laser scanner operates at laser scanner operates at 1535 nm1535 nm. At this wavelength, . At this wavelength, higher energy levels can be used without running the risk to hurt the higher energy levels can be used without running the risk to hurt the eye. eye.

Intensity of return laserIntensity of return laser

ALS system intensity (or strength) of the return laserALS system intensity (or strength) of the return laser

importantimportant

White sandWhite sand, most of the emitted beam will be reflected , most of the emitted beam will be reflected back to the aircraftback to the aircraft

Black bitumen roadBlack bitumen road, much less of the beam will be, much less of the beam will be

reflected backreflected back

Backscattering properties of targetBackscattering properties of target

Reflectivity of various materials for 900 nm wavelengthsReflectivity of various materials for 900 nm wavelengths____________________________________________________________________________________________________________________________

Material Material Reflectivity (%)Reflectivity (%)____________________________________________________________________________________________________________________________

SnowSnow 80-9080-90White masonryWhite masonry 8585Limestone, clayLimestone, clay up to 75up to 75Deciduous treesDeciduous trees Typ.60Typ.60Coniferous treesConiferous trees Typ.30Typ.30Carbonate sand (dry)Carbonate sand (dry) 5757Carbonate sand (wet)Carbonate sand (wet) 4141Beach sandBeach sand Typ.50Typ.50Concrete, smoothConcrete, smooth 2424Asphalt with pebblesAsphalt with pebbles 1717LavaLava 88____________________________________________________________________________________________________________________________

(Wehr and Lohr, 1999)(Wehr and Lohr, 1999)

Maximum Range vs. Target Reflectivity of LMS-Q280iMaximum Range vs. Target Reflectivity of LMS-Q280i

Riegl web page

ALS and Atmospheric conditionALS and Atmospheric condition

ALS best performance is achieved when the atmosphere ALS best performance is achieved when the atmosphere is is cool, dry and clearcool, dry and clear

IR propagation is severely attenuated by IR propagation is severely attenuated by water vapour,water vapour,

(rain, fog and/or humidity), CO2(rain, fog and/or humidity), CO2

Dust particles and smokeDust particles and smoke also reduce detection range also reduce detection range

BestBest result during result during night,night, worstworst during day with during day with brightbright

sunlightsunlight

Physical properties in Laser ScanningPhysical properties in Laser Scanning

High powerHigh power

Short pulsesShort pulses

High collimationHigh collimation

Narrow optical spectrum (10 nm bandwidth)Narrow optical spectrum (10 nm bandwidth)

Narrow optical spectrumNarrow optical spectrum has an has an advantageous, advantageous, because narrow optical interference filters can be because narrow optical interference filters can be mounted in the receiving path to suppress disturbing mounted in the receiving path to suppress disturbing background radiation, caused by backscattered background radiation, caused by backscattered sunlight.sunlight.

Position and Orientation System (POS)Position and Orientation System (POS)

The 3D position of a point on the earth surface can be The 3D position of a point on the earth surface can be computed, if the computed, if the position and orientationposition and orientation ( (POS)POS) of the laser of the laser system is known with respect to a coordinate system. system is known with respect to a coordinate system.

Integrated Integrated POSPOS consisting of consisting of DGPSDGPS and an Inertial and an Inertial Measurement Unit Measurement Unit (IMU)(IMU)

Geocoding of laser scanner measurements requires anGeocoding of laser scanner measurements requires an exact exact synchronization synchronization of all systems : IMU, DGPS andof all systems : IMU, DGPS and laser scanner datalaser scanner data

Time synchronization of better than 10 µs in achievedTime synchronization of better than 10 µs in achieved operationally by this schemeoperationally by this scheme

Wehr and Lohr (1999)Wehr and Lohr (1999)

Determination of laser pointsDetermination of laser points

After a surveying flight, basically two data sets are available:After a surveying flight, basically two data sets are available: the the POS dataPOS data and the and the laser rangeslaser ranges with the instantaneous with the instantaneous scanning angles.scanning angles.

Data Data visualization and manual editingvisualization and manual editing is necessary in different is necessary in different stages of the processing chain.stages of the processing chain.

Major advancements have been achieved by improvement mainly of Major advancements have been achieved by improvement mainly of the the post-processing softwarepost-processing software and less of the laser scanner and less of the laser scanner hardware.hardware.

Interpolated data can be further processed and analyzed by Interpolated data can be further processed and analyzed by commercial software e.g. commercial software e.g. Scop, Microstation, EASI-PACE, and Scop, Microstation, EASI-PACE, and ARC/INFO.ARC/INFO.

Currently, the Currently, the processing timeprocessing time for a DTM computed from laser for a DTM computed from laser scanner data is typically scanner data is typically three timesthree times the data acquisition time. the data acquisition time.

Processing steps in ALS dataProcessing steps in ALS data

Typical processing steps for laser scanner data

POS Data(DGPS, IMU)

Ranges and ScanAngels

Calibration Dataand Mounting Parameters

Laser PointsX, Y, Z in WGS84

orLat., Long., H in WGS84

Map Projection

Sorting

Filtering

Rasterizing and

Thinning Out

Case studyCase study

Airborne laser scanning and high resolution satellite data for Geomorphic

study in Elbe river valley, Germany

(Anbazhagan et al 2005)

ObjectiveObjective

Integration of high resolution satellite data with Airborne Laser Scanner (ALS) data to study the various geomorphic features in parts of Elbe river valley, Saxony, Germany.

Study areaStudy area

Elbe basin in parts of Sächische Schweiz National park zone is mostly covered by forest

Airborne laser scanning data give more informations on terrain condition covered under dense forest and enable to interpret the different types of landforms

Data used Airborne Laser Scanning (ALS) data was obtained from TopScan

GmbH, Germany

The density of ALS cloud point is 1 point per 9 sq m area. The accuracy of height is in between ± 10.8 cm and ± 12.6cm

IKONOS satellite data acquired on 1st August 2000 is used in the present study. The satellite data in digital format is obtained from Hansa Luftbild GmbH, Germany.

The imagery covered 97 sq km area in parts of Sächsischen Schweiz region

IKONOS satellite data comprises of panchromatic band (PAN) with 1m spatial resolution and four multi-spectral bands with 4m spatial resolution.

Multi-spectral bands were merged with geometrically rectified PAN data (1m resolution). The output image has 1m spatial resolution with 8 bit format

Software used Software used

The laser point cloud data were processed with The laser point cloud data were processed with help of help of SCOP++SCOP++ software developed by Institute software developed by Institute of Photogrammetry and Remote sensing, of Photogrammetry and Remote sensing, Technical University, ViennaTechnical University, Vienna

IKONOS satellite data & DEM,DSM, DGM done IKONOS satellite data & DEM,DSM, DGM done through through Erdas imagine 8.7Erdas imagine 8.7 image processing image processing softwaresoftware

IKONOS-PAN IKONOS-PAN

IKONOS- MULTISPECTRALIKONOS- MULTISPECTRAL

IKONOS_ PAN + MSS MERGEDIKONOS_ PAN + MSS MERGED

IKONOS_High pass filterIKONOS_High pass filter

IKONOS_ Histogram equalisation IKONOS_ Histogram equalisation

IKONOS-Elbe river valleyIKONOS-Elbe river valley

Digital Elevation Model generated from Laser point data, Elbe river valley

Digital Surface Model (DSM) derived from ALS data

ALS Digital Surface Model showing different landforms

Terrace surface and River Terraces in ALS DSM

IKONOS FCC superimposed over DSM data

IKONOS TCC + DSM DATA

IKONOS TCC + DSM DATA

ALS Digital Ground Model (DGM), Part of Elbe river basin

Airborne Laser Scanning data – Shaded relief, Elbe river basin

Geomorphology in parts of Elbe river basin (based on IKONOS and ALS data)

AIRBORNE LASER SCANNING: OTHER AIRBORNE LASER SCANNING: OTHER APPLICATIONS APPLICATIONS

Digital Elevation ModelsDigital Elevation Models

DTM (Digital Terrain Model)DTM (Digital Terrain Model)DEM (Digital Elevation Model) DEM (Digital Elevation Model) DSM (Digital Surface Model)DSM (Digital Surface Model)DCM (Digital Canopy Model)DCM (Digital Canopy Model)DGM (Digital Ground Model)DGM (Digital Ground Model)

DTM and DSM generation in urban areas, automated building DTM and DSM generation in urban areas, automated building extraction, generation of 3-D city models for urban planning, extraction, generation of 3-D city models for urban planning, wireless telecommunication, microclimate models, wireless telecommunication, microclimate models, propagation of noise and pollutantspropagation of noise and pollutants

High accuracy and very dense measurement applications e.g. High accuracy and very dense measurement applications e.g. flood mapping, DTM generation and volume calculation in flood mapping, DTM generation and volume calculation in open pit mines, road design and modelingopen pit mines, road design and modeling

Disaster ManagementDisaster Management

Rapid mapping and damage assessment Rapid mapping and damage assessment after natural disaster after natural disaster

e.g after e.g after hurricanes, earthquakes, landslideshurricanes, earthquakes, landslides etc.,etc.,

NRSC has done ALS survey in NRSC has done ALS survey in TsunamiTsunami affected areaaffected area

Mapping of Corridors Mapping of Corridors

Mapping corridors e.g. roads, railway tracks, Mapping corridors e.g. roads, railway tracks, pipelines, waterway landscapespipelines, waterway landscapes

Mapping of electrical transmissions lines and Mapping of electrical transmissions lines and towers including ground / tree clearancetowers including ground / tree clearance

DTM generation, especially in forested areas (in DTM generation, especially in forested areas (in forest road and path planning, drainage, etc)forest road and path planning, drainage, etc)

Urban City ModelingUrban City Modeling

ALS data has become an important source for ALS data has become an important source for generating generating high quality 3D urban city modelinghigh quality 3D urban city modeling..

3D city model using high resolution IKONOS 3D city model using high resolution IKONOS

imagery and airborneimagery and airborne laser scanning data (Tao laser scanning data (Tao and Yasuoka 2002).and Yasuoka 2002).

Digital Surface Models (DSM) acquired at Digital Surface Models (DSM) acquired at different occasions to successfully detect the different occasions to successfully detect the building changesbuilding changes (Murakani et al 1999). (Murakani et al 1999).

Terrain MappingTerrain Mapping

Landscape modeling using Landscape modeling using integrated integrated airborne multi-airborne multi-spectral and laser scanning data (Hill et al 2002).spectral and laser scanning data (Hill et al 2002).

Generation of digital surface models and digital elevation Generation of digital surface models and digital elevation models that can provide information on the models that can provide information on the geomorphology geomorphology of the earth’s surface (Pereira and of the earth’s surface (Pereira and Wicherson 1999). Wicherson 1999).

Merging of high resolutionMerging of high resolution satellite data and airborne laser satellite data and airborne laser scanning data provide information geomorphological scanning data provide information geomorphological features like cuesta, mesa, escarpments and river terraces features like cuesta, mesa, escarpments and river terraces (Anbazhagan et al 2005)(Anbazhagan et al 2005)

Forest Resource MappingForest Resource Mapping

ALS technology can provide information about ALS technology can provide information about tree tree height, crown diameter, tree density, and biomass height, crown diameter, tree density, and biomass estimation. estimation.

Vegetation height is a function of species Vegetation height is a function of species composition, climate and site quality, and can be composition, climate and site quality, and can be used for used for land cover classificationland cover classification. .

Forest Forest structure and biophysical parametersstructure and biophysical parameters, and , and digital elevation models for watershed delineation digital elevation models for watershed delineation and water flows.and water flows.

(A) The unprocessed lidar height surface (i.e., digital surface model, DSM), (B) elevation surface (i.e., digital terrain model, DTM), and (C) the estimated vegetation height surface (i.e., digital canopy model, DCM) resulting from the subtraction of the DTM (B) from the DSM (A).

Clark et al 2004

Management of Fluvial zonesManagement of Fluvial zones

Accurate and updated models of flood plains are critical Accurate and updated models of flood plains are critical for flood plain monitoring and disaster planning.for flood plain monitoring and disaster planning.

Laser data used to generate Laser data used to generate hydrodynamic modelhydrodynamic model. Such . Such model is determine the effect of high water levels and of model is determine the effect of high water levels and of earth works, such as removal of sand in river areas earth works, such as removal of sand in river areas (Pereira and Wicherson 1999). (Pereira and Wicherson 1999).

LIDAR and Photogrammetry data used for monitoring LIDAR and Photogrammetry data used for monitoring water elevation and volume changes in riparian water elevation and volume changes in riparian resources within the Grand Canyon region (Davis et al resources within the Grand Canyon region (Davis et al 2002).2002).

Coastal zone ManagementCoastal zone Management

Highly dynamic coastal zone require constant Highly dynamic coastal zone require constant updating of baseline survey data. ALS offers a updating of baseline survey data. ALS offers a cost effective method to do this on a routine cost effective method to do this on a routine basis. basis.

Mapping and monitoring of shore lines, beaches, Mapping and monitoring of shore lines, beaches, tidal flats, dunes, and wetlands. tidal flats, dunes, and wetlands.

Measurement of coastal areas, determination of Measurement of coastal areas, determination of coastal change and erosioncoastal change and erosion

HIGWAY ENGINEERINGPROJECTSHIGWAY ENGINEERINGPROJECTS

LIDAR pointsLIDAR points

DTMDTM

DTM from LIDAR + DTM from LIDAR + aerophotgrammetric elementsaerophotgrammetric elements

HIGWAY ENGINEERINGPROJECTSHIGWAY ENGINEERINGPROJECTS

The product generated by DSM, orthophotos The product generated by DSM, orthophotos mosaic and highway geometric project mosaic and highway geometric project integration made possible a high quality integration made possible a high quality visualization of highway project. This product visualization of highway project. This product can be used as much visualization element for can be used as much visualization element for customer project presentation as for public customer project presentation as for public hearings.hearings.

Coastal Bathymetric studiesCoastal Bathymetric studies

Bathymetric layers operated same principle as the Bathymetric layers operated same principle as the

topographic lasers, but emit in two wavelength, usually topographic lasers, but emit in two wavelength, usually 1064 nm and 532 nm.1064 nm and 532 nm.

The infrared wavelength is reflected on the water The infrared wavelength is reflected on the water surface, while the green one penetrates the water and surface, while the green one penetrates the water and reflected by bottom surface or other objects in the reflected by bottom surface or other objects in the water.water.

Laser data used for water depth measurement and Laser data used for water depth measurement and monitor the submerged jetty and disposal areasmonitor the submerged jetty and disposal areas..

ALS development ALS development

1995 LIDAR commercial operations 5 world wide1995 LIDAR commercial operations 5 world wide

2001 75 organizations 60 sensor commercial2001 75 organizations 60 sensor commercial

2002 120 organizations 75 sensors2002 120 organizations 75 sensors

2005 150 – 200 sensors2005 150 – 200 sensors

Major commercial sensors N.America (50%), Europe (28%) 15% Asia-Major commercial sensors N.America (50%), Europe (28%) 15% Asia- pacific mostly Japanpacific mostly Japan

Remote Sensing 9.1% annual growth rateRemote Sensing 9.1% annual growth rate

Forecast 2006 – LIDAR, SAR, Hyperspectral dataForecast 2006 – LIDAR, SAR, Hyperspectral data

(Lohani and Flood, 2003)(Lohani and Flood, 2003)

$30 - $50 million per year for Lidar data acquisition $30 - $50 million per year for Lidar data acquisition

growth in the rate 20% - 40%growth in the rate 20% - 40%

30% private sector in USA , leading market 30% private sector in USA , leading market

energy utilitiesenergy utilities

35% state/local government35% state/local government

35% federal government35% federal government

ALS development ALS development

Conclusion Conclusion Airborne Laser scanning data is an accurate, Airborne Laser scanning data is an accurate,

fast and versatile measurement technique, fast and versatile measurement technique, and open up new exciting area of application.and open up new exciting area of application.

Integration of airborne laser data and high Integration of airborne laser data and high resolution satellite data will give excellent resolution satellite data will give excellent information on landscape modelinginformation on landscape modeling

Potential integration with imaging sensors is Potential integration with imaging sensors is expected to put airborne data acquisition on expected to put airborne data acquisition on a revolutionary level of system performance a revolutionary level of system performance

ReferencesReferences

Abbott,R.H., Penny,M.F., 1975. Abbott,R.H., Penny,M.F., 1975. Ackermann. F., 1999. Ackermann. F., 1999. Anbazhagan,S., Trommler.M., Csaplovics.E., 2005 Anbazhagan,S., Trommler.M., Csaplovics.E., 2005 Cunningham,L.L., 1972.Cunningham,L.L., 1972.Davis.P.A., et al., 2002. Davis.P.A., et al., 2002. Haala,N., Brenner,C., Anders,K.H., 1997. Haala,N., Brenner,C., Anders,K.H., 1997. Hill.R.A., and Veitch.N., 2002Hill.R.A., and Veitch.N., 2002Hill et al 2002. Irish.L.J, Lillycrop.W.J. 1999. Hill et al 2002. Irish.L.J, Lillycrop.W.J. 1999. Kushwaha.S.P.S., and Behera.M.D., 2002.Kushwaha.S.P.S., and Behera.M.D., 2002.Lohani.B., and Flood.M., 2004Lohani.B., and Flood.M., 2004Maas, H.G., and Vosselman.G.,1999. Maas, H.G., and Vosselman.G.,1999. Murakami et al (1999). Murakami et al (1999). Pereira.L.M.G, Weicherson.R.J.1999 Pereira.L.M.G, Weicherson.R.J.1999 Tao.G., Yasuoka.Y., Tao.G., Yasuoka.Y., Vosselman.G., Suveg.I., 2001 Vosselman.G., Suveg.I., 2001 Wehr.A., and Lohr.U., 1999. Wehr.A., and Lohr.U., 1999. Wulder. M., Onge,B., Treitz.P., 2000.Wulder. M., Onge,B., Treitz.P., 2000.

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