Airborne Lidar Calibration Approaches Defining calibration techniques and assessing the results
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Transcript of Airborne Lidar Calibration Approaches Defining calibration techniques and assessing the results
Airborne Lidar Calibration Approaches Defining calibration techniques and assessing the results
JAMIE YOUNGLIDAR SOLUTIONS SPECIALIST
LiDAR: Light Detection and Ranging
Aerial sensorCollects/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 GPSMeasures the location of the aircraft up to 0.1 second relative to a known ground position
LiDAR Collection Sensors
• Optech• Leica• Toposys• Reigl
Sensor Type Pulse Speed Maximum Altitude
Single Pulse 167 kHz 600m
Multi-Pulse 167 kHz 1100m
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
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LiDAR CalibrationWhy 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
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Flying lines perpendicular Flying lines parallel Calibration every mission
Lidar Calibration
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Flying a cross flight during collection
Lidar Calibration
Planar SurfaceCalibration process finds planar surfaces
The Plane ResultsGraphically speaking
Roof Line Correction
Roof Line Correction
Checking CalibrationDZ ortho from several missions
Checking CalibrationDifferences between bad calibration and correct calibration
Unresolved Area Resolved Area
Checking Calibration4 missions - old calibration method
Difficult Collections and Data
Applications
Applications
Hydro Breakline Collection Process (LiDARgrammetry)
Additional Classification• Smooth Water Bodies• Vegetation - Low, Medium, High• Buildings - Points, Footprints
Data1.4 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 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?
Publications
LIDAR for Dummies American Surveyor – Mobile Mapping Professional Surveyor –Calibration
Software
WILDER LiDAR Blog
http://bloglidar.wordpress.com
Thank You