Airborne Lidar Calibration Approaches Defining calibration techniques and assessing the results

1
Airborne Lidar Calibration Approaches Defining
calibration techniques and assessing the results

• JAMIE YOUNGLIDAR SOLUTIONS SPECIALIST

2
LiDAR Light Detection and Ranging
Aerial GPS (Global Positioning System) Based on
GPS satellite triangulation, measures the
location of the aircraft up to 0.1 second.
Aerial sensor Collects/scans data, either photons
(reflected light) or laser pulses
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
3
LiDAR Collection Sensors

• Optech
• Leica
• Toposys
• Reigl

Sensor Type Pulse Speed Maximum Altitude
Single Pulse 167 kHz 600m
Multi-Pulse 167 kHz 1100m
4
LiDAR Project Planning

• Plan based on
• Flightline distance limitations
• Workable blocks of data
• Delivery tiles
• Baseline requirements
• Control locations
• Accuracy
• Application
• Topography

5
LiDAR Project Planning

• 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

6
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

7
Establishing Control
8
GPS

• Static initialization at start
• Static session at end
• PDOP less than 3

• Processing is easier
• Achieve under 5 cm combined solution

9
IMU data
Accelerometer
Gyro
Lever arms
10
Lidar Products

• 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

11
Specialized Lidar

• 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

12
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 It Important?
LiDAR CalibrationWhy is this 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

13
14
Lidar Calibration

• Flying lines perpendicular
• Flying lines parallel
• Calibration every mission

14
15
Lidar Calibration

• Flying a cross flight during collection

15
16
Planar Surface

• Calibration process finds planar surfaces

17
The Plane Results

• Graphically speaking

18
Roof Line Correction
19
Roof Line Correction
20
Checking Calibration

• DZ ortho from several missions

21
Checking Calibration

• Differences between bad calibration and correct
  calibration

Unresolved Area Resolved Area
22
Checking Calibration

• 4 missions - old calibration method

23
Difficult Collections and Data
24
Applications
25
Applications
26
Hydro Breakline Collection Process
(LiDARgrammetry)
27
Additional Classification

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

28
Data1.4 meter collection
DSM- Digital Surface Model
Intensity Image
29
Innovations
30
Whats 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

31
Check Point Surveys

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

32
Verification of Point Class
Legend High Vegetation Points Medium
Vegetation Points Bare Soil points
33
Accuracy

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

34
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?
35
Publications

• LIDAR for Dummies
• American Surveyor Mobile Mapping
• Professional Surveyor Calibration Software

36
WILDER LiDAR Blog

• http//bloglidar.wordpress.com

37
Thank You