prinsip lidar

8/10/2019 Prinsip Lidar

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PRINSIP ALAT LiDAR

JARAK = ( Laju cahaya x Masa ) / 2

Pengukur Jarak Laser (Cahaya)

Teknologi ini menggunakan cahaya laser. Ia dapat mengukur

jarak dengan mengukur ketumpatan cahaya laser yang

dibalikkan. Dengan menggunakan asas matematik, kedudukan

sesuatu jarak dapat diketahui dengan persamaan di bawah :


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PENGEN L N teknologi LiD R

LiDAR adalah satu kaedah pengukuran ketinggian para

mukabumi dengan menggunakan teknologi laser

Satu sistem penderiaan aktif, boleh menembusi awan

nipis

Data asas yang telah diortorektifikasi

Mengatasi masalah kelewatan pengukuran titik kawal

bumi


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LIDAR ACCURACYVertical

better than 15 cm at 1,200 m

better than 35 cm at 3,000 m

Horizontal

better than 1/2,000 x altitude


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PERB NDING N RINGK S FOOTPRINT

D N G RIS PENERB NG N

Camera and lens

Type

Image Size

(mm)

Focal Length

(f) (mm )

Field of

View

(degree

)

Image Scale at

1000m flying

height (H)

(f/H)

Footprint at

1000m flying

height

(meter)

No. of

f l ight

l ines for

30x30km

and 30%

sidelap

RC 30 Narrow 230 x 230 600-610 30-35 1:1666 383.2 x 383.2 111

RC 30 Normal 230 x 230 300-305 60-80 1:3333 766.6 x 766.6 56

RC 30 Wide 230 x 230 150-153 90-95 1:6666 1533.2 x 1533.2 28

RC 30 Super wide 230 x 230 85-88 120-130 1:11764 2705.7 x 2705.7 16

ALTM-DCS

37 x 37

(4077x4092

pix) 55 36

1:18181

(*GSD=0.163m) 667.1 x 669.6

66

ALSS- ALTM 3070 - -

50

(max) -

932.6

(swath width)

46

*GSD = Ground Sample distance

= pixel size x im age scale factor

= 0.009 mm x 18181

= 0.163m


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2ndReturn

3rdReturn

2ndReturn

3rdReturn

1stReturn

Last Return

Pulse Rate Frequency(PRF)

First-pulse Mengukur jarak bagi objek pertama

yang dipantulkan.

Contoh disebelah menunjukkanpantulan cahaya pada pokok dan tanahdisekitarnya.

Last-pulse Mengukur jarak bagi objek terakhir

yang dipantulkan. Contohnya seperti bangunan, tanah,

pokok, bukit, air dan sebagainya.

Bersambung

PRINSIP LiDAR

(1) Pantulan Laser


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4 PANTULAN LASER

YANG DIAMBIL

1stReturn

Last Return3rdReturn

2ndReturn


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PRINSIP PANTULAN LiDAR

Altitude (km) Hz< 1.5 < 70,000

< 2.0 < 50,000

< 3.0 < 33,000


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CIRI-CIRI PANTULAN LiDAR

Highly Reflective Materials = Strong Return

Signal

Faktor-faktor Yang Mempengaruhi Pantulan : Ketinggian (Elevation)

Kandungan (Composition)

Kepadatan (Density)

Orientasi/Kedudukan ke sensor (Orientation to thesensor)

High Reflectivity: Permukaan Tanah Cerah

Rumput

Pokok

Air (berombak/ bergerak)

Low Reflectivity: Permukaan TanahGelap

Tanah Hitamspt.Tar, Tanah

Berturapdll (Asphalt)

LombongBatuArang(Coal)

Permukaan Basah (Wet surface) Kasawan Berlumpur (Mud)

Air(tidak berombak)


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PRINSIP LiDAR

( 2 ) Scanning

Depending on the laser altimeter used and the altitude of operationabove ground spot sizes of 20 cm (8") to 25 m (85 ft) and strip widths of

50 m

(150 ft) to 9 km (6 mi) can be achieved.

o Scan Rate: < 70 Hz

o FOV: < 25 (Half Angle)


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Laser Foot Print Narrow beam

divergence

Spread of laser

limits accuracy iflaser spot on

ground gets too

large

Spot sizes of 5 30 cm are useful

and necessary for

canopy

penetration

D = H*a

Where:

D = Spot Size

H = Height

a = Beam

Divergence

Angle in Radius

D

Ha


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LiDAR MENGGUNAKAN AIRBORNE LASER SCANNING SYSTEM (ALSS)

LiDAR menggabungkan tiga teknologi canggih iaitu :

Kedudukan kapalterbang ditentukan menggunakan teknologi

penentuan titik sejagat/ kedudukan(Global Positioning System:

GPS). Keadaan/orientasi kapalterbang (Yaw, Pitch and Roll) semasa

pengukuran

direkodkan menggunakan sistem INS (Inertial Navigation System) /

IMU

(Inertial Measurement Unit), Jarakdari ALSS ke mukabumi di ukur menggunakan laser


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Ketiga tiga data ini kemudiannya digabungkan untuk menghitung koordinat

mukabumi dalam 3 dimensi.

Ketepatan yang dapat diperolehi menggunakan teknologi ini dilapurkan

sebanyak +/- 15cm bagi satah pugakdan =/- 0.5 m bagi kedudukan

mendatar


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LiDAR(ALSS-Airborne Laser Scanning System & DCS-Digital Camera

System)Combined

Computer Rack

Sensor Head

Operator &Flight

Navigation

InterfaceLaptop

(1)

(2)

(3)

(4)

Digital Camera

(5)

ALSS

DCS


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LiDAR basic output

( 2 ) Digital Image

( 1 ) Laser Points

Digital images of Cameron Highlands

Laser points of Cameron Highlands


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Produk LiDAR

(1) Data Intensity

4000 shades of Gray ScaleRecorded at all flight altitudes

(2) Bahagian Ketinggian (Shaded Relief)

(3) Kontur

(4) Grid/TIN

(6) Ortofoto**

(5)DTM/DE

M


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APLIKASI DATA LiDAR

( 1 ) Urban Survey( 2 ) Power Line Mapping

( 3 ) Flood Simulation

( 4 ) Vegetation Removed

( 5 ) Forestry & Biomass Estimates

( 6 ) Coastal Areas : Erosion

Monitoring

( 7 ) Flood Study( 8 ) Disaster Assessment

( 9 ) Urban Mapping


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( 1 ) Urban SurveyDowntown Toronto

Ortofoto & Kadester Lot


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( 2 ) Power Line MappingCanada

Route assessment

Vegetation encroachment assessmentPrevention of accidental power line cut-off

Electrical load assessment

Forest fire preventionSafety assessment

( 6 ) E si


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1998199920002001

( 6 ) ErosionMonitoring

Coastal Areas

Erosion area


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( 8 ) Disaster AssessmentTaiwan

LiDAR C & P ssi Ti Esti ti


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Assumptions :

Flying Ht : 1000 m (~3300 ft)

Speed : 100 knots (~50m/sec)

Field Of View : 37o

Swath Width : 669 m

Flying Times : 1 hour

Estimation :

Unclassified Processing Time : 120 sq km/hour

Laser Points Processing Time : 8-12 hours

LiDAR Coverage & Processing Time Estimation


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Sensors

Laser +

Receiver

System

GPS/IMU

Digital Imaging

System

Post-Processing

Laser Pulse

Range Data

Lat, Long, Height,

Roll, Pitch, Heading

Digital Images(TIFF, JPEG, IMG)

Output

LAS(LIDAR Point

Data Records)

X, Y, Z point data

Geo-Referenced

Image (GeoTIFF)

Raw

Data

Processed

Data

Intensity

MeasurementFeature Classification

Aided by Intensity Measurement

ALSS d DCS P i


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ALSS and DCS Processing

Overview

POSPAC

Airborne & Base

Station GPS Processing

SBET Files Processing

Blending GPS & IMU Data

REALM

Importing a BETDefine Polygon

Processing Laser Points

Defining Processing Area

Combining Laser Points

Output Laser Points

(First and last pulse an Intensity)

TERRASCAN

Clean DataClassification

Manually QC Clean

Geoid Correction

Surface

Contour

TERRAMODELLER

Lattice Grid

Contour Editting

Point Cloud

DEM

ALSS

(Airborne Laser Scanning System)

ORTHOPRO (ISAT)

Create Project

Setup Camera With IO Parameters

Drag In Images Import EO File

Ortho Rectification

Seam Line Generation

IMAGEVUE / IMAGEMISSION

Downloading

Developing

RGB

Dark and Gain Correction

Image View

REALM

ALTM System

ALTM Tapes

Decoding Tapes

Creating a Database

Adding a Database

PRODUCTS

DEM

Contour

PRODUCTS

Orthophoto

SBET File Output

ISAT Ready ImageDCS

(Digital Camera System)


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SYNTHETIC APERTURE RADAR (SAR)

Satellite-based, stereo SAR processing

Data source: RadarSat 1

Acquired in 2003 DEM and orthorectified imagery by Q4,

2003

DEM Accuracy: 25 m


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SYNTHETIC APERTURE RADAR (SAR)

SAMPLE IMAGE


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SYNTHETIC APERTURE RADAR (SAR):

PRODUCTS

DEMOrthoimage

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