Considerations for Planning, Acquiring, and Processing LIDAR Data for Forestry Applications

1. Considerations for Planning, Acquiring, and Processing LIDAR Data for Forestry Applications Robert J. McGaughey USDA Forest Service--PNW Research Station Hans-Erik Andersen University of Washington-Precision Forestry Cooperative Stephen E. Reutebuch USDA Forest Service--PNW Research Station Pacific Northwest Research Station-Silviculture and Forest Models Team University of Washington-Precision Forestry Cooperative

2. Outline • Brief LIDAR overview • LIDAR data characteristics & deliverables • QA/QC procedures • Data processing • Introduction of FUSION software • Conclusions

3. LIDAR • Light Detection and Ranging • 4 types • Atmospheric • Continuous waveform • Discrete return (profiling) • Discrete return (scanning) • Airborne Laser Scanning (ALS) • Discrete return (scanning) mounted on aircraft

4. ALS System Components • Scanning laser emitter-receiver unit • Differentially-corrected GPS • Inertial measurement unit (IMU) • Computer to control the system monitor mission progress • Interesting targets

5. Multiple Returns • Many laser systems can record several returns for each pulse • Multiple returns occur when the laser beam is only partially blocked • Part of the laser energy is reflected back to the sensor • The remaining laser energy continues downward • Up to 5 returns per pulse • Typically only 2-3 returns • Many systems record the amount of energy reflected by target objects • Intensity (near-infrared, 1064 nm)

6. Multiple Returns All returns (16,664 pulses) 1st returns 2nd returns (4,385 pulses, 26%) 3rd returns (736 pulses, 4%) 4th returns (83 pulses, <1%)

7. Comparison With Other Remote Sensing Technologies • Active sensor • Laser pulse is emitted and reflected energy is measured • Passive systems rely on reflected solar energy • Returns are actual measurements • Range is computed based on round-trip travel time for laser energy • Combined with accurate aircraft position and attitude to produce XYZ point measurement • Small footprint at target • 30-100 cm footprint at ground surface • 4+ pulses/m2 is common • Multiple returns over porous targets

10. LIDAR Accuracy • RMSE provided by LIDAR system manufacturers • 10-15cm vertical • 50-100cm horizontal • Several studies provide independent verification of these values • Ground survey points • Tree heights • Building heights • Alignment of power transmission lines

11. LIDAR DEM Bare-Earth Accuracy • Mean LIDAR DEM error • 22 cm…9-inch field boot height! • Maximum errors: • +1.3 meter, -0.63 meter…(+4.3 ft, -2.1 ft) • Error is not significantly affected by canopy density

12. LIDAR Data Characteristics • High spatial resolution • Typical density is 0.5-6 pulses/m2 • 2-3 returns/pulse in forest areas • Surface/canopy models typically 1-5m grid • Large volume of data • 5,000-60,000 pulses/hectare • 12,500-150,000 returns/hectare • 0.3-3.6 Gigabyte/hectare

13. “Typical” Mission Specifications

14. Deliverables:General Considerations • Delivery format • Return data, surfaces, images, GIS coverages • Can you read the format? • Does the data contain all the information you need? • Delivery media • External hard drives are common but not easy to backup to more stable media • You would like to be able to retrieve single data files from your backup • What do you do with multiple DVDs? • How do you know what has been delivered? • Contracts need to include specific deliverables to help you assess overall data quality and completeness • Deliverables based on the actual data…not just coverage area boundaries • Do you have adequate storage space to move data onto faster devices? • Disk space • Bandwidth

15. Deliverables:Common Data Products • Metadata • Flight information • LIDAR system settings • Data coverage • Bare ground products • Bare-ground returns • Surface models • Return data • Coarse filtering to remove outliers • Includes return number • Always get the return data for a project • Adds very little to contract cost • Will cost you $$ if you decide you want it later

16. Deliverables:Forestry-Specific Products • Canopy height models • Normalized using bare-ground surface • Filtered to remove buildings, powerlines, and other above-ground features • Canopy cover maps • Presence/absence of vegetation • Vegetation density (percent cover) • Geo-referenced LIDAR intensity images • First return intensity value (reflected energy) • Useful an “image” (B/W IR image) • Useful as a layer for further analysis

17. QA/QC Assessment:Did you get what you ordered? • Initial delivery: • Missing data • Missing returns • Misclassified returns • Tile naming inconsistencies • Contractor used custom software to produce ASCII formatted data • Several flight lines were omitted • They had no way to view the ASCII files • They didn’t know what they delivered • Over 60 client-hours to sort out the problems • Contractor made 3 deliveries over a 5-week period

18. QA/QC Assessment:Quality and Completeness

19. Data Processing:What do I do with all these points? Raw data are interesting to look at but require extensive processing to create useful information

20. Data Processing:Bare-Earth Surface Model

21. Data Processing:Canopy Surface Model

22. Final Products:Canopy Height (Raw Data)

23. Final Products:Percent Cover (2.5m grid)

24. Final Products:LIDAR Intensity Image (5m grid) 1m grid

25. Coniferous/Deciduous Classification Using Intensity Values (Raw Data)

26. LDV Data viewer FUSION Data interface Sample options • Shape & size • Coloring rules • Snap to POI Color Motion Tree data Canopy model Lighting Glyph Image Bare-earth model PDQ Simple Data viewer Measurement Command line processing and utility programs LIDAR data Hotspots Points of interest (POI) FUSION Software

27. FUSION Software • Displays several kinds of data • Allows users to interactively select portions of large datasets for viewing • Users can “mine” the data to discover new information • Clips all data layers and makes them available for detailed 3D viewing • Supports stereoscopic viewing • Runs on a current hardware • Available through RSAC…included on DVD you were given at registration…demos on Thursday

28. Main System components • FUSION – 2D interface to several data types • Allows extraction of data subsets • Interacts with LDV to display samples • Includes tools to develop images using LIDAR point cloud (colored by elevation or intensity) • LDV – 3D data visualization • Very interactive • Provides a variety of display options • Allows direct measurement in data • Provides structured measurement protocol for measuring tree attributes • Provides analysis framework for prototyping analysis strategies

29. Conclusions • LIDAR can help foresters characterize spatial variability in forest conditions at resolutions beyond our wildest dreams • Cost is decreasing while LIDAR system capabilities are increasing • Analysis procedures are being defined and refined

30. Conclusions • The number of commercial LIDAR providers is increasing • More competition, more work, more interest in uses other than bare-earth modeling • Large LIDAR acquisitions are underway • Foresters and other resource specialists need to be “at the table” when decisions regarding data specifications are made • Raw return data is always valuable even if the analysis tools and methods are not fully mature • FUSION will be demonstrated Thursday