An Overview of

LiDAR Operations

Rob McCarthy

John Chance Land Surveys

Lafayette, Louisiana, USAILMF 2009 – New Orleans

John Chance Land Surveys

• Part of Fugro

– Geospatial Services Group

• Design and build both FLI-MAP LiDAR systems

and LiDAR processing software

• Operated LiDAR systems commercially since

1995

What is LiDAR?

• LiDAR is another tool in the

surveyors tool box

– Like a total station, level or RTK unit

– To be used when it is the most

appropriate tool for the job

What is LiDAR

• LiDAR is the application of a

number of modern technologies:

– Positioning

– Inertial technology

– Laser scanning

– Digital imagery

to provide fast, efficient and cost-

effective surveys using established

survey principles

Key LiDAR Components

• Most airborne LiDAR systems, regardless of type have basically similar key components

• Positioning

• GPS

• Airborne

• Base station

• Typically a “post-processed kinematic” solution

• Inertial Measurement Unit (IMU)

• Navigates between GPS updates

Key LiDAR Components

• Range Measurement

– Scanning laser

• Angular Measurement

– Inertial Measurement Unit (IMU)

• Accurate pitch, roll & yaw

How it All Works

GPS Satellites

GPS Receivers

Base Station

Understanding LiDAR Specs

Effective Laser Pulse Rate 150,000 or 250,000 pulses per second

Multiple Return Capability Yes - Maximum of 4 returns per pulse

Laser Intensity Capture Yes – For all laser returns

Laser Eye Safety FDA Certified Class 1 laser

Eye safe at the aperture

Laser Point Density Approx 70 points per square meter @ 100m altitude and

20m/s speed

Laser Ranging Accuracy 1 cm

Laser Swath Angle 60 degrees – Swath width approximates to flying height

Laser Look Angles Nadir

Forward looking (7 degrees)

Rear looking (7 degrees)

Maximum Operating Height 400 meters

Understanding LiDAR Specs

• Pulse Rate– Laser Pulse Rate

– Effective Laser Pulse Rate

• Return Capability– Single

– Multiple

– Waveform Analysis

• Accuracy– Total System

– Component

– Absolute

– Relative

• Eye Safety

• MPIA

LiDAR Accuracy

• Accuracy statements

– RMSE

– 1 sigma (67% confidence)

– 2 sigma (95% confidence)• 20cm at 2σ is approx 10cm RMSE

• Total LiDAR system accuracy

– Affected by a number of factors:• Platform positioning

• Pointing angles

• Laser spot size

• Laser ranging

Improving LiDAR Accuracy

• Improve platform positioning

– Multiple independent positioning

solutions

– Multiple short base lines for kinematic

processing

• Reduce effect of pointing angle

errors and spot size

– Fly lower

What is MPIA

• MPIA is multi pulse in air

• At high laser pulse rates, maximum

altitude is limited by the speed of light

• MPIA allows more than one pulse to be in

the air allowing high pulse rates to be

used at higher altitudes

• The latest sensors offer this technology

Types of Airborne LiDAR

Wide Area Systems

Corridor Mapping

Systems

• Bathymetric LiDAR

• Topographic LiDAR

Wide Area LiDAR

• Wide area LiDAR is typically

characterized by:

– Fixed-wing platform

– High altitude data collection

– Wide swath width

– Low point density

– Low resolution

– Lower levels of accuracy

– Non eye-safe laser

Corridor Mapping LiDAR

• Corridor Mapping LiDAR is typically

characterized by:

– Helicopter platform

– Low altitude data collection

– Narrow swath width

– High point density

– High resolution

– Higher levels of accuracy

– Eye-safe laser

Additional Sensors

• LiDAR systems are often fitted with additional

sensors which can provide useful information to

accompany the LiDAR data

• Digital Imagery

– Video

– Still

Additional Sensors• Orthophotography

• Infra-red cameras

Wide Area vs Corridor

• The differences are as much related to data

collection methods as they are to hardware

– Data collection altitude and speed (helicopter vs fixed

wing)

– Number of base stations (multiple vs single)

– Length of GPS baselines (short vs long)

• These factors affect the efficiency, and therefore

price, of data collection per unit area

Applications

• LiDAR can be used for many tasks

as a replacement for conventional

land survey or aerial

photogrammetry

• The type of LiDAR system that is

most appropriate for the job will

depend on specifications and

deliverables

Wide Area Applications

• Base mapping

– Lidar DEMs are accurate for orthorectification as well as for contour generation with supplemented 3D breaklines.

• Floodplain mapping

– Lidar data supports flood hazard analyses and hydrologic and hydraulic modeling.

• Natural resources management

– Lidar data is used to calculate tree-stand heights, biomass, and timber volumes and is useful in establishing volume calculations for mineral extraction.

Wide Area Applications

• Transportation and utility

corridor mapping

– LiDAR data can supplement

traditional ground and aerial surveys

in the planning and design of new

transportation and utility corridors.

• Urban modeling

– 3D models from bare-earth and

reflective-surface lidar data can be

used in analysis and visualization of

urban planning, line-of-sight studies,

etc.

Corridor Applications

• Transmission Lines

– Lidar data is suited for design, rebuild and thermal rating analysis. LiDAR data interfaces well with engineering packages such as PLS-CADD

• Railways

– Lidar data supports engineering design, GIS population and track data requiredfor Positive Train Control

• Highways

– Lidar data can be used to provide accurate data for highway design

Corridor Applications

• Levees

– Lidar data is suited for as-built assessment of levees, including generation of levee cross sections and damage assessment

• Pipelines

– Lidar data supports engineering design for new pipeline routes

• Area Projects

– Those that require the level of detail and accuracy provided by a corridor mapping system

Deliverables

• A LiDAR “point cloud” looks

impressive, but is of little use to

most clients

• Accuracy, detail and deliverable

requirements will dictate which type

of LiDAR system should be used for

data collection

• Raw LiDAR data sets are very large

– Filtering

– Digitizing

– Vectorizing

can reduce data sets to be

manageable, while maintaining

accuracy and detail

Deliverables

• LiDAR data processing is a large subject on its own but is

outside of the scope of this presentation

LiDAR Misconceptions

• All LiDAR systems are basically the same

– Technically, some components are similar, but

they are optimized to provide data sets that can

differ greatly

• More points are always better

– Just because you can does not mean that you

should

– The highest quality LiDAR data set is not

required for every project

– Using an appropriate system for a project should

ensure you get the data you need and provide

the most “bang for the buck”

LiDAR Misconceptions

• LiDAR point density is purely a function

of laser pulse rate

– Laser point density is a function of:

• Laser pulse rate

• Data collection altitude

• Data collection speed

• The angle of the laser swath

– A 150,000 Hz system operated at 6,000 feet and

at 120mph will provide a very different data set to

a 150,000 Hz system operated at 300 feet and

40 mph

LiDAR Misconceptions

• LiDAR data can only be collected “leaf

off”

– Some LiDAR points can reach the ground

through gaps in the tree canopy

– Performance in vegetated areas is optimized by

• High point density

• Small laser spot size

• Multiple return capability

– Mid day sun analogy

– However, there is a limit

Vegetated ROW1st Returns2nd Returns3rd Returns4th ReturnsFull Filtered

Ground Set

Multiple Returns

LiDAR Misconceptions

• LiDAR replaces traditional mapping

techniques– LiDAR in general cannot completely replace

conventional survey

– LiDAR cannot identify the following features:

• Boundary information

• Underground utilities

• Water or water depth

– Edge of water will

be mapped

– Conventional survey

still needed for construction

staking etc.

LiDAR Misconceptions

• LiDAR is an all-weather system– Although LiDAR has fewer weather limitations than

photogrammetry there are significant weather

limitations

• Target must be able to reflect the laser (near infra-red)

light

• Does not work well on snow covered ground

– Degraded data set

– Survey would be “top of snow”

– Imagery (if required) is poor

• Does not work well through precipitation (rain, fog,

snow)

• It is very difficult to fly accurate flightlines in high and

gusty wind conditions

LiDAR Advantages

• LiDAR can offer considerable advantages

over conventional survey or

photogrammetry for the right project

– Fast data collection

– Fast data processing (dependent on

deliverables)

– Little or no need for access

– Less weather dependent than

photogrammetry

• Night operations

– Not if imagery is required

LiDAR Advantages

– LiDAR performs better in vegetated areas

than photogrammetry

• Able to collect data in “leaf on” condition

– Robust data sets with many possible

products

– In office data mining

• No need to return to the field to collect more data

– Cost savings for the right project

• Economies of scale

Questions?

Booth #18

John Chance Land Surveys – FLI-MAP (Corr Map)

Fugro Earthdata – ALS-50 (Wide Area)

Fugro Horizons – ALS-50 (Wide Area)

Fugro SESL – FLI-MAP (Corr Map)

Fugro Pelagos – SHOALS 1000T (Bathymetric)

Geospatial

Services