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LiDAR

LiDAR. An Introduction and real-world applications. Presented by Steven Menefee Mahinda Abeykoon. LiDAR - Outline. Introduction to LiDAR What is it? History Platforms Major Components Acquisition Resultant Raw Data LiDAR Data Derivatives Real-World Applications

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LiDAR

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  1. LiDAR An Introduction and real-world applications Presented by Steven Menefee Mahinda Abeykoon

  2. LiDAR - Outline • Introduction to LiDAR • What is it? • History • Platforms • Major Components • Acquisition • Resultant Raw Data • LiDAR Data Derivatives • Real-World Applications • Sedgwick County LiDAR • How was it collected • Data received • What did we use it for • Q/A Image courtesy ASPRS

  3. LiDAR – So What is it? • LiDAR - Light Detection And Ranging • Light = “Active” Laser • Detection = Laser is reflected and detected by a receiver • Ranging = Distance (Time x Speed of Light/2) • Analogies • Bat • Lightning/Thunder • Drop rock .0001 secs .0002secs 186,282 mi/sec = 18.6 Miles / 2 * .0001 secs Image courtesy DougDraws

  4. Modern LiDAR – A Brief History • Why ? • NASA – Measure Atmospheric properties • When? • 60s – First instruments • 70s – Airborne Profilers • 80s – GPS/INS • 90s – Scanners replace Profilers • 2000s – Heavy commercialization • Why so prevalent now? • Hardware more capable (DGPS, more capable scanners) • Software more capable (handle more points)

  5. LiDAR Platforms • Airborne (Our focus) • Rotary • Fixed wing • Spaceborne • Topography • Atmosphere • Terrestrial • Mobile –Driverless Car • Static • Wind Turbine • Police Images courtesy Penn State, NASA, The Economist, MattersNetwork, Photocop, Geoinformatics

  6. Airborne LiDAR - Components • Global Positioning System • Laser System • Laser Source • Scanning Mechanism (swath) • Laser Detector • Inertial Navigation System (INS) • Computer • Aircraft

  7. Components - GPS • Major hurdle for Airborne LiDAR • Need 4 Satellites • Base Station (known location) • Differential GPS (DGPS) required for accuracy • Provides location of Aircraft to the cm GPS Base Station (Differential Correction)

  8. Components – Laser System • Laser Source • Why laser? • Monochromatic • Directional (unlike flashlight) • Pulse Rate (around 100-150 kHz) • Infrared • Forms cone, not line (misconception) • Scanning Mirror Mechanism • Allows for swath • Types (next slide) • Laser Detector/Receiver Beam Divergence Post Spacing Laser Footprint

  9. Laser Scanning Mechanisms

  10. Components – Inertial Navigation System • Aircraft not stationary • Records Attitude • Angle the Laser is pointing • Small degrees = Big Impact Image courtesy The Blaze, Remote Sensing Core Curriculum

  11. Components – Computer • Ties together all of components • Records thousands of pts/sec (calculates) • 103 mb to 1.4 gb per Sq Mi (stores) • Allows for on-the-fly (realtime) georeferenced points

  12. Components - Visual GPS Satellites Inertial Navigation System 37.6749,-97.9282,3329 37.5023,-97.0823,3923 37.9234,-97.3523,3866 37.3432,-97.6432,3502 Aircraft Computer Laser/Scanning Mechanism 0.1932,-0.6013,3 0.2230,-0.0301,1 0.4321,-0.6321,5 0.1223,-0.5623,7 Differential Corrections Laser Receiver GPS Base Station (Known Point) 37.3362, -97.6462, 1200

  13. Acquisition – Single Return Point Cloud Posting Density Height Along Track Post Spacing Cross Track Post Spacing

  14. Acquisition –Multiple Returns Beam Divergence 1st Return Height 2nd Return 5km 3rd Return 4th Return 1 km Not always the ground 0.3m 1.5m

  15. Multiple Returns – Real Visual Image courtesy Hans-Erik Anderson

  16. Common Point Data Formats • ASCII (.txt) • Simple Text • Easily Read • Not Proprietary • Long Processing Time • LAS (.las) • Binary file • Not Proprietary • Must have software • Efficient/Fast/Header Image courtesy NOAA

  17. LiDAR Accuracy • Dependent upon • Scan Angle • Flying Height • Pulse Rate • GPS Configuration • Base Station Distance • Elevation ≈ 0.2 to 1 ft • Horizontal ≈ 0.3 to 1.5 ft • Talk with vendor Image courtesy Merchant Circle

  18. LiDAR – Advantages/Disadvantages Advantages Disadvantages • Millions of Points • Day or Night • Quick turnaround • Penetrate Canopy Gaps • Rule of thumb - sunshine • Massive Datasets • Indiscriminate • No Breaklines • Abrupt breaks in elevation • Rivers, buildings, etc

  19. LiDAR Derivatives Digital Elevation Models Contours TIN Hillshade Slope Aspect

  20. Derivatives – Digital Elevation Models • Most common derivatives • Easier than Managing Mass Points • Modeling based on surfaces • Interpolation between points • DTM–Digital Terrain Model • Bare Earth – Points Filtered • Normally Breaklines Enforced • Hydrologic modeling • DSM–Digital Surface Model • First returns • 3D Visualization • Line of Sight Applications • TIN–Triangulated Irregular Network • Vector • Quick rendering TIN Images courtesy Aerometrex and Wikipedia

  21. Derivatives - Contours • Vector Representation • Lines of equal Elevation • Easy to Read • Draws Quickly • Familiarity

  22. Derivatives - Hillshade • Theoretical Light Source • Visualize in 3D • DEM Overlay • Cartographic

  23. Derivatives – Slope/Aspect • Slope • Steepness • Rate of Change • Aspect • Cardinal Direction • “Slope Direction”

  24. LiDAR - Applications Images courtesy Oregon State University

  25. Real-World Applications – Hydrology • FEMA Floodplain Maps • National Research Council, 2007 - ”LiDAR is the most cost effective technology to acquire elevation information over large regions to support floodplain mapping to FEMA accuracy standards” • Green – LiDAR, Red - FEMA • Watersheds • Elevation Key • Drop of water Images courtesy NOAA, John Dorman NC Flood Mapping Program, William & Mary, Directions Mag, N. Carolina Cooperating Technical State

  26. Real-World Applications – Line of Sight • Good use of DSM • Radio/Cell Phone Towers • Planning and Zoning • Event Security Image courtesy ESRI

  27. Real-World Applications – Solar Potential • Gauge Solar Energy Potential • Slope (angle) /Aspect (direction) Image courtesy ESRI

  28. Real-World Applications – Forestry • Canopy Height • $3/acre vs $30/hr • Hours vs Years • Canopy Fuel Capacity • Timber Inventory Images courtesy Oregon State University

  29. Real-World Applications – Utilities • Map Right of Way Corridors • Encroachments • Powerline Curvature/Clearance Images courtesy Penn State, Geoplace, Geoinformatics,

  30. Thank you for your time! Please save all tough questions for Mahinda

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