Dot-to-dot recent progress in UAS LiDAR: calibration, accuracy assessment, and application

Transcription

1 Dot-to-dot recent progress in UAS LiDAR: calibration, accuracy assessment, and application Arko Lucieer, Colin McCoull, Richard Ballard, Steve Harwin, Deepak Gautam, Darren Turner Surveying and Spatial Sciences Group School of Land & Food

2 Outline Development of commercial laser scanners for UAS TerraLuma UAS LiDAR brief history Design of latest TerraLuma UAS LiDAR Lever arm offset measurements Boresight calibration Accuracy assessment Application in pinus radiata plantation

3 Laser scanning

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5 Commercial developments

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7 Wallace, L., Lucieer, A., Watson, C., & Turner, D. (2012). Development of a UAV-LiDAR System with Application to Forest Inventory. Remote Sensing (UAV special issue), 4(6), doi: /rs

8 Detection of pruning Wallace, L., Lucieer, A., and Watson, C. (2014). Detecting pruning of individual stems using Airborne Laser Scanning data captured from an Unmanned Aerial Vehicle. International Journal of Applied Earth Observation and Geoinformation, 30 (1), 76-85, doi: /j.jag

9 UAS SfM vs LiDAR Wallace, L., Lucieer, A., Malenovský, Z., Turner, D., Vopěnka, P. (2016). Assessment of forest structure using two UAV techniques: a comparison of airborne laser scanning and structure from motion (SfM) point clouds. Forests, 7(62), doi: /f

10 Geometric distortions 1 error in pitch, roll, or yaw can introduce a spatial error of 34 cm for a flying height of 20 m, and 1.75 m at 100 m flying height. Combined effect is worse. Small low-cost IMUs 1 accuracy best-case pitch/roll, much worse in heading

11 Dual antenna, dual frequency GNSS: 2 4 cm position, 0.15 heading Devourer X8 heavy-lift multi-rotor Brushless gimbal for sensor stabilisation Intel NUC data logger Velodyne VLP-16 Puck Machine vision camera Spatial Dual GNSS/IMU Electronics: voltage regulation and synchronisation

12 Video

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16 Lever arm offsets

17 Lever arm offsets CAD

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23 Calibration timing offset!

24 Boresight calibration

25 Boresight angles α

26 Before boresight calibration: ghosting

27 Before boresight calibration

28 After boresight calibration

29 After boresight calibration

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31 Point density Scan Line number of returns number of last returns covered area in square meters per length (in km) point density: all returns (per m2) spacing: all returns (m) point density: last returns (per m2) spacing: last returns (m) / / / / / / / All Flights Combined /

32 Difference between strips and reference surface Scan Line Raw calibrated flight lines Mean Distance (m) Std. Deviation Flight lines following rigid body transformation Mean Distance Std. Deviation (m) m m

33 Known distances Measurement and Surveyed Distance (m) between Targets Scan Line TL to TR GL to GR Tl to GR TR to GL TL to TR m m m m m Average Combined Average 0.001m (Range -0.12m to 0.096m) TL = Building target to west TL = Building target to east GL = Central western ground target in front row (row next to building) GR = Central eastern ground target in front row (row next to building)

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35 Terrestrial laser scan (TLS)

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37 50 m AGL

38 70 m AGL

39 Conclusions UAS are an effective tool to capture vegetation structure at very high density LiDAR calibration for lever arm offsets and boresight angles is critical UAS LiDAR can collect extremely dense point clouds: pts/m 2 for typical flying heights m Absolute accuracy 7.8 cm from direct georeferencing; 4.6 after adjustment Next steps: Individual tree identification Separation of under-, mid-, overstory Characterisation of complex natural ecosystems Stem detection in pre-harvest stands

40 Acknowledgements Mr Richard Ballard, Dr Steve Harwin, Dr Darren Turner, Dr Josh Kelcey, Mr Tony Veness, Dr Zbynek Malenovsky, Dr Colin McCoull, Mr Deepak Gautam, Mr Iain Clarke, Drs Christopher Watson & Jon Osborn (UTAS) Dr Luke Wallace (RMIT) Forest and Wood Products Association (FWPA) Dr Christine Stone (DPI NSW) Australian Research Council (ARC) Australian Antarctic Division (AAD) Central Science Lab (CSL) & Engineering workshop School of Land and Food and UTAS support

41 Web: Web: