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