Airborne Lidar Calibration Approaches Defining calibration techniques and assessing the results

1. Airborne Lidar Calibration Approaches Defining calibration techniques and assessing the results JAMIE YOUNGLIDAR SOLUTIONS SPECIALIST

2. LiDAR: Light Detection and Ranging Aerial GPS (Global Positioning System) Based on GPS satellite triangulation, measures the location of the aircraft up to 0.1 second. Aerial sensor Collects/scans data, eitherphotons (reflected light) or laser pulses IMU (Inertial Measurement Unit) Measures attitude (pitch/yaw/roll) of aircraft every.002 second. Ground GPS Measures the location of the aircraft up to 0.1 second relative to a known ground position

3. LiDAR Collection Sensors • Optech • Leica • Toposys • Reigl

4. LiDAR Project Planning Plan based on Flightline distance limitations Workable blocks of data Delivery tiles Baseline requirements Control locations Accuracy Application Topography

5. Day or Night Safety considerations Leaf on or Leaf off Application dependent Summer, Spring, Fall, or Winter Most collects done in the spring and fall Summer collects take place for special applications such as forestry Winter collects based on geographic location Weather Smoke LiDAR Project Planning

6. Establishing Control • Establish control for entire mapping program prior to collection using a minimum of two HARN and/or CORS stations and a minimum of three Vertical Bench Marks • Perform Fully Constrained Network Adjustment • Apply HDTP corrections to published • positions (as necessary) • Adjustment supports a mapping • operation not a survey • Provide adjustment to all LiDAR • providers involved in the program • prior to processing

7. Establishing Control

8. GPS • Static initialization at start • Static session at end • PDOP less than 3 • Processing is easier • Achieve under 5 cm combined solution

9. IMU data Accelerometer Gyro Lever arms

10. Standard LIDAR – Nominal 1m point spacing 15 cm RMSEz vertical accuracy Hydro Enforced breaklines 20foot nominal widths for rivers 1acre lakes/ponds General-use, Meets most needs for LiDAR-based DEM Supplemental 2 foot accuracy specifications USGS Compliant LIDAR – Nominal 1m – 2m point spacing 15 cm RMSEz Vertical Accuracy FEMA Map Modernization specified product Hydro Enforced Breaklines 100foot nominal widths for rivers 2acre lakes/ponds Points removed off breaklines in separate class 1m – 3m DEM Metadata Processing and Vertical Assessment Reports High Accuracy LiDAR – 0.7m or more Point spacing 9.24 cm RMSEz Supplemental 1 foot accuracy specifications 50% overlap for very dense vegetation Supplemental breaklines Vertical Assessment Report provided Requires very good calibration: Keep overlap Lidar Products

11. Data collection as required by client Breaklines generated from intensity images Contour products Sample density – 8 points per meter and higher or 4 meter postings and lower 3-D building extraction Clients requiring additional classification Water Vegetation Buildings Specialized Lidar

12. Lidar Calibration - Critically Important • Optech and Leica have calibration procedures • Proprietary sensors have custom procedures • Proper installation and lever arm • Survey standardization • GPS survey of antenna • Total station survey of antenna • PosPAC location of antenna

13. Lidar Calibration: Why Is It Important? LiDAR CalibrationWhy is this Important? • Calibration after every installation • Required to make sure the system is operating correctly • Calibration every mission • Provides necessary information in case of unforeseen occurrences • Fly a minimum of 1 perpendicular line to flight lines collected for that mission • Ensure ability to correct for roll, pitch, heading, scan scale and other potential biases • 90% of problems are a result of improper installation 13

14. Lidar Calibration • Flying lines perpendicular • Flying lines parallel • Calibration every mission 14

15. Lidar Calibration • Flying a cross flight during collection 15

16. Calibration process finds planar surfaces Planar Surface

17. Graphically speaking The Plane Results

18. Roof Line Correction

19. Roof Line Correction

20. DZ ortho from several missions Checking Calibration

21. Differences between bad calibration and correct calibration Checking Calibration Unresolved Area Resolved Area

22. 4 missions - old calibration method Checking Calibration

23. Difficult Collections and Data

24. Applications

25. Applications

26. Hydro Breakline Collection Process (LiDARgrammetry)

27. Additional Classification Smooth Water Bodies Vegetation - Low, Medium, High Buildings - Points, Footprints

28. Data1.4 meter collection DSM- Digital Surface Model Intensity Image

29. Innovations

30. What’s Important? Relative Accuracy Removal of Artifacts and Outliers How do you quantify this? Gaps Unacceptable Vegetation Removal & Other Classifications How do you quantify this? Check Point Verification Horizontal Accuracy Vertical Accuracy

31. Check Point Surveys Five Main Categories Hard Surface Low Grass High Grass Brush Forest What does this mean? By region? Point distribution?

32. Verification of Point Class Legend High Vegetation Points Medium Vegetation Points Bare Soil points

33. Accuracy • NSSDA standard • NMAS specification • FEMA specification • ASPRS specification • RMSE What accuracy do you need? What are you doing?

34. Typically Speaking? • Vertical accuracy required usually 9 -18.5 cm • Horizontal accuracy required usually 30 cm – 1.0m • Before MPia, ALS-60, and GEMINI • Vertical accuracy achieved: 7 -12 cm • Horizontal accuracy achieved: 45cm -2.0m • After MPia, ALS-60 and GEMINI • Vertical accuracy achieved: 3 – 12 cm • Horizontal accuracy achieved: 10 – 27 cm • Data meets accuracy specification?

35. Publications • LIDAR for Dummies • American Surveyor – Mobile Mapping • Professional Surveyor –Calibration Software

36. WILDER LiDAR Blog http://bloglidar.wordpress.com

37. Thank You