AN INTRODUCTION TO LASER SCANNING

PART 1

LIDAR• YOU WILL OFTEN HEAR THE TERM ‘LIDAR’

• LIGHT DETECTION AND RANGING• OR A COMBINATION OF THE WORDS LIGHT AND RADAR

• TECHNOLOGY TO MEASURE DISTANCES BY ILLUMINATING A TARGET WITH A LASER AND ANALYSING THE REFLECTED LIGHT TO DETERMINE DISTANCE

• NUMEROUS PLATFORMS, APPLICATIONS AND TECHNIQUES

HOW DOES IT WORK?

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TYPES OF LASER SCANNER• THERE ARE MANY DIFFERENT TYPES OF LASER SCANNER

• THE MOST COMMON TYPES FOR SURVEYING ARE:• TIME OF FLIGHT (PULSE-BASED)• PHASE SHIFT

• LATEST SCANNERS CAN MEASURE UP TO 1 MILLION POINTS PER SECOND

TIME OF FLIGHT SCANNERS• PULSE OF LIGHT EMITTED BY LASER SOURCE

• LIGHT IS REFLECTED OFF AN OBJECT BACK TO LASER SENSOR

• SPEED OF LIGHT IS KNOWN SO WE CAN CALCULATE DISTANCE

time

PHASE SHIFT SCANNERS• SIMILAR CONCEPT TO TIME OF FLIGHT SCANNERS

• CONSTANT BEAM OF LASER ENERGY IS EMITTED

• SCANNER MEASURES THE PHASE SHIFT OF THE RETURN LASER ENERGY TO CALCULATE DISTANCE

WHICH SCANNER?

Scanner Type

Pros Cons

Time of Flight

Good range(1m – 6km), multiple target capability

Expensive

Phase Shift Cheap, slightly more precise

Low maximum range (<500m), can have ambiguous measurements

WAVEFORM DATA - MULTIPLE TARGETS

WAVEFORM DATA - MULTIPLE TARGETS

WAVEFORM DATA - MULTIPLE TARGETS

Rock face with fine mesh- Jwaneng Diamond Mine, Botswana

WAVEFORM DATA - MULTIPLE TARGETS

WAVEFORM DATA – DIGITIZING AND ANALYSIS• THE ENTIRE WAVEFORM IS CAPTURED AND DIGITIZED• EXTRACTED ECHOES AT A CERTAIN TIME PROVIDE RANGE• ADDITIONAL INFORMATION ABOUT THE SHAPE OF THE PEAK INDICATES

QUALITY

WAVEFORM DATA – DIGITIZING AND ANALYSIS• MULTIPLE ATTRIBUTES CAN BE MEASURED FROM THE WAVEFORM DATA

LASER SCANNER INTENSITY• INTENSITY IS THE STRENGTH OR

AMPLITUDE OF THE RETURN SIGNAL

• THE INTENSITY DECREASES WITH RANGE AND ANGLE OF INCIDENCE

• SOME SCANNERS ARE CALIBRATED TO TAKE DISTANCE INTO ACCOUNT, THIS IS KNOWN AS REFLECTIVITY

AMPLITUDE & REFLECTIVITY

Amplitude Reflectivity

MEASURING IN 3D• LASER SCANNERS USE A MOVING MIRROR TO MEASURE ON A 2D PLANE

• ROTATING POLYGON MIRROR • OSCILLATING MIRROR

• TO MEASURE IN 3D THE SCANNER MUST EITHER:• ROTATE

• TRIPOD BASED SCANNER• MOVE

• PLATFORM MOVES PROVIDING A TRAJECTORY• EXAMPLES INCLUDE HELICOPTERS, FIXED WING, CARS, UAVS ETC.

DO YOU WANT TO KNOW MORE?

IF SO, GO TO WWW.3DLASERMAPPING.COM FOR MORE INFO, OR GIVE US A CALL

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