What type of scanners do Airborne laser scanning systems use? How do they work and why? This presentation covers the basics of Airborne Laser Scanning and some important things to consider if looking at this technology. If you would like more information on this technology or you are looking for a system yourself? Please get in touch - www.3dlasermapping.com / info@3dlasermapping.com

1. AN INTRODUCTION TO LASER SCANNING
PART 2 – AIRBORNE LIDAR, THE BASICS
OF TRAJECTORIES

2. TRAJECTORIES
• AIRBORNE LIDAR SYSTEMS USE 2D SCANNERS
• THE 3RD DIMENSION IS DERIVED FROM THE MOVEMENT OF THE AIRCRAFT
• THE PRECISE POSITION AND ORIENTATION OF THE LIDAR SYSTEM IN THE AIRCRAFT IS KNOWN AS
A TRAJECTORY
• TIME
• FROM GNSS
• POSITION - LATITUDE, LONGITUDE, ELEVATION
• FROM GNSS
• ORIENTATION (ATTITUDE) - HEADING, ROLL, PITCH
• FROM IMU

3. GLOBAL NAVIGATION SATELLITE SYSTEM (GNSS)
• GNSS’ EMPLOY A CONSTELLATION OF ORBITING SATELLITES TO PROVIDE GEOGRAPHICAL POSITION
AND VELOCITY INFORMATION
• MANY SYSTEMS ARE IN USE AT THIS TIME, WITH THE MOST POPULAR INCLUDING:
• UNITED STATES - GLOBAL POSITIONING SYSTEM (GPS)
• RUSSIA – GLOBAL NAVIGATION SATELLITE SYSTEM (GLONASS)
• CHINA – COMPASS / BEIDOU NAVIGATION SYSTEM (BDS)
• EUROPEAN UNION – GALILEO
• RECEIVERS THAT CAN TRACK MULTIPLE GNSS CONSTELLATIONS WILL GENERALLY PROVIDE MORE
ACCURATE POSITIONAL DATA, ESPECIALLY IN URBAN CANYONS WHERE SKY VISIBILITY IS LIMITED

4. GLOBAL NAVIGATION SATELLITE SYSTEM (GNSS)
• DUE TO ERROR SOURCES SUCH AS ATMOSPHERIC INTERFERENCE AND SATELLITE CLOCK TIMING,
GNSS RECEIVERS ARE OFTEN ONLY ACCURATE TO 1-2M
• ACCURACY CAN BE IMPROVED USING METHODS SUCH AS:
• PRECISE POINT POSITIONING (PPP) - <30CM
• POST-PROCESSING AGAINST A REFERENCE STATION – DIFFERENTIAL GNSS (DGNSS) - < 2CM
• REAL TIME KINEMATIC (RTK) CORRECTION - < 2CM
• GNSS IS USUALLY LOGGED AT 2-10HZ
• ONE POSITION MEASURED EVERY 0.1-0.5 SECONDS

5. INERTIAL NAVIGATION SYSTEM (INS)
• AN INS IS A COMBINATION OF AN INERTIAL MEASUREMENT UNIT (IMU) AND A CONTROL
COMPUTER
• THE INS IS INITIALLY PROVIDED WITH ITS POSITION AND VELOCITY FROM AN EXTERNAL SOURCE,
AND FOR AIRBORNE LIDAR THIS IS GNSS
• A KALMAN FILTER COMBINES THE DIFFERENT MEASUREMENTS TAKING INTO ACCOUNT ESTIMATED
ERRORS TO PRODUCE A TRAJECTORY

6. INERTIAL MEASUREMENT UNIT (IMU)
• MEASURES ROTATION AND ACCELERATION
• COMBINED WITH POSITION AND VELOCITY FROM GNSS RECEIVER TO PRODUCE A
TRAJECTORY
• TWO MAIN TYPES OF IMU
• FIBRE OPTIC GYRO (FOG)
• MICRO ELECTRO MECHANICAL SYSTEM (MEMS)
• IMUS USUALLY LOG BETWEEN 100-500HZ

7. TYPICAL AIRBORNE LIDAR TRAJECTORY

8. TYPICAL AIRBORNE LIDAR POINTCLOUD

9. DO YOU WANT TO KNOW MORE?
IF SO, GO TO WWW.3DLASERMAPPING.COM FOR MORE
INFO, OR GIVE US A CALL
UK: +44 1949 838 004
South Africa: +27 12 940 0515
Australia: +61 (0) 8 9261 7703
North America: +1 720 214 3554