Airborne Lidar Calibration Approaches Defining calibration techniques and assessing the results JAMIE YOUNG LIDAR SOLUTIONS SPECIALIST

LiDAR: Light Detection and Ranging Aerial sensor Collects/scans data, either photons (reflected light) or laser pulses Aerial GPS (Global Positioning System) Based on GPS satellite triangulation, measures the location of the aircraft up to 0.1 second. 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

LiDAR Collection Sensors Optech Leica Toposys Reigl Sensor TypePulse SpeedMaximum Altitude Single Pulse167 kHz600m Multi-Pulse167 kHz1100m

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

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

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

Establishing Control

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

IMU data Accelerometer Gyro Lever arms

 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

 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

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 this Important? Lidar Calibration: Why Is It 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

14  Flying lines perpendicular  Flying lines parallel  Calibration every mission Lidar Calibration

15  Flying a cross flight during collection Lidar Calibration

Planar Surface Calibration process finds planar surfaces

The Plane Results Graphically speaking

Roof Line Correction

Checking Calibration DZ ortho from several missions

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

Checking Calibration 4 missions - old calibration method

Difficult Collections and Data

Applications

Hydro Breakline Collection Process (LiDARgrammetry)

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

Data 1.4 meter collection DSM- Digital Surface Model Intensity Image

Innovations

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

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

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

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

Typically Speaking? Vertical accuracy required usually cm Horizontal accuracy required usually 30 cm – 1.0m Before MPia, ALS-60, and GEMINI Vertical accuracy achieved: 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?

Publications  LIDAR for Dummies  American Surveyor – Mobile Mapping  Professional Surveyor –Calibration Software

WILDER LiDAR Blog

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