LiDAR – What is it and How is it Used? Presented by John Erickson Project Manager Ayres Associates February 13, 2003 Presented by John Erickson Project Manager Ayres Associates February 13, 2003

Objectives of Presentation What is LiDAR How is LiDAR used – Project Example Future Development of LiDAR What is LiDAR How is LiDAR used – Project Example Future Development of LiDAR Introduction

Outline of Presentation LiDAR system components Typical LiDAR mission for a two foot DEM Future development of LiDAR software & hardware LiDAR system components Typical LiDAR mission for a two foot DEM Future development of LiDAR software & hardware Introduction

LiDAR What Is LiDAR? Light Detection And Ranging (LiDAR) is the optical equivalent of radar or sonar but using an optical source – a laser - instead of microwaves or sound waves. An optical pulse is emitted from a laser and the instrument accurately measures the time until an “echo” or return pulse(s) are recorded. The time is converted to a distance to the target using known speed of light (Time of Flight).

LiDAR What Are the Core Technologies Involved? Rugged compact laser rangefinders (LIDAR) Highly accurate inertial measurement units (IMU) Global Positioning Satellite system (GPS) Compact, rugged instrument installed on a small aircraft. Laser pulses scanned across the path of the aircraft measuring range to surface. LiDAR ranges combined with aircraft GPS position and IMU orientation information. Post-processing software calculates XYZ position of each spot on the surface. LiDAR mapping is based on a combination of three mature core technologies: Fast, powerful, computers with large storage capacities make everything easier.

Lidar Laser Altimetry LiDAR provides range information (R). GPS provides position information (X, Y, Z). IMU provides orientation information ( , ,  ). Scanner angle (  ) also required. Solve transformation of (X, Y, Z, , , , , R) to generate geo-referenced point on the target.

Lidar Instrument Manufacturers Optech (ALTM) Azimuth (AeroScan) TopEye Proprietary Designs: – –ALTMS (TerraPoint), TopoSys, FLI-MAP (John Chance) Research Systems (SLICER, LVIS, ATM) 70 Systems deployed worldwide, Jan 2002

LiDAR Typical LiDAR Mission for a Two Foot DTM Example project – Pima County, AZ Ayres Associates, Airborne 1 and I.K. Curtis team Airborne : LiDAR data collection I.K Curtis: Aerial Photography Ayres Associates: Photogrammetry

LiDAR LiDAR Mission Specifications for a Two Foot DTM 25 KHz LiDAR system - System takes 25,000 measurements per second, collecting simultaneous first and last returns. Flying Height 4500’ AGL Digital Elevation Model (DEM) in ASCII XYZ format 1.5 meter spacing of DEM

LiDAR Accuracy Statement from Airborne 1 As stated by the manufacturer, and verified by periodic system calibrations, our airborne laser terrain data is: 1. Vertically accurate to 15 cm at a 90% confidence interval 2. Horizontally accurate at better than 1/3000 th the flying height at the same 90% confidence interval. This accuracy is defined and derived from checks of complete data sets on flat open surfaces. This level of accuracy has not been stated for areas of dense vegetation or sudden breaks. Any gridding or interpolation of the raw data will naturally diminish the accuracy of the terrain representation.

LiDAR Airborne 1 Deliverables Bald earth and the vegetation in ASCII XYZ points files on CD-ROM. All LiDAR points files provided by Airborne 1 will be in the NAD 83 horizontal and NAVD 88 vertical systems All points files will be tiled to 100MB. Any additional tiling will be priced separately according to your needs. “Intensity Data” for each laser shot if desired. This is simply an additional column of data with a grayscale value for each laser shot, indicating the reflectivity of the ground or surface.

LiDAR LiDAR Mission Components Ground Control Terrain and Flight Lines Acquiring LiDAR data Data Processing Data management

LiDAR LiDAR Ground Control LiDAR Calibration Site –Calibration Site usually near project –Consists of identifiable objects that have been ground surveyed –Calibration site is flown before and after each mission Ground Control for GPS Base Stations –Within 30 Km of project –Provides post processed derived X,Y,Z position of aircraft

LiDAR Terrain and Flight Lines Identify ground features for determining flight line spacing –Mountain ranges –Restricted airspace Weather conditions –Prevailing winds –Daily temperature variations –Pollution levels –Day vs. Night time missions

LiDAR LiDAR Flight Plan

LiDAR Acquiring LiDAR data Fly over calibration site Navigate to project area Follow flight plan using GPS navigation Data collection - Juggle operation on IMU, Airborne GPS receiver, and Laser Fly over the calibration site at mission end Perform initial quality checks Back up data

LiDAR Data Processing Each flight line produces a dataset that contains: –Absolute GPS position –Inertial attitude information –Laser ranging vectors Information above is combined to produce X, Y, and Z coordinates of each laser strike point Resultant data set is referred to as a “point cloud” “Point Cloud” can be classified using first/intermediate/last return information and intensity data

LiDAR Data Processing Classification First/Last return –Used to differentiate between land cover and bald earth Intermediate returns –Can be used for further classification of land cover, i.e. tree canopy vs. ground cover vegetation vs. bald earth

LiDAR Vegetation Example Vegetation Penetration Here is the point “cloud” with vegetation canopy and ground shots.

LiDAR Vegetation Example Vegetation Penetration Here is another shot of the same area, with the vegetation in place.

LiDAR Vegetation Removal

LiDAR Data Processing Classification Intensity Data –Gray scale value (1 – 255) assigned to each laser return depending on the energy level of the return –Can be used to create an “image” which helps with classification of returns –Intensity data can be color coded to help with visualization

LiDAR Intensity Data

LiDAR Intensity Draped on DEM

LiDAR Data Processing Classification Software Proprietary software is offered by instrument manufacturers to owners. (xyz only) Increasing number of third-party packages available to address LiDAR data analysis and classification (e.g. Terrasolid’s TerraScan (Microstation Add-On)

LiDAR Data management LiDAR data sets are massive Pima County Project Area 1 alone has 177,768,889 points (400 square Km) Delivery media include 8mm tape, DVDs, and CDs

LiDAR Pima County Project – Two Foot Contours from LiDAR Data Breaklines need to be added to LiDAR data to produce two foot contours that meet NMAS or ASPRS specifications. –DEM spacing, although extremely dense, can’t properly model terrain. –Today, there is no automated way to produce breaklines from LiDAR data –Breaklines to be added through stereo compilation –Final quality check using soft copy photogrammetry

LiDAR Directions in Hardware Higher Point Densities Better penetration of bare earth thru canopy Better characterizations of canopy elements Better representation of terrain breaks Better delineation of man-made features

LiDAR Directions in Hardware Intensity Imagery Useful in editing terrain models Useful in delineating features Maybe useful in evaluating surface characteristics Can be obtained in low-light conditions Eliminates some need for ancillary imagery

LiDAR Directions in Hardware Smaller and lighter equipment Reduced power requirements Use of other wavelengths Use of multiple wavelengths Integration with other sensors UAV platforms

LiDAR Directions in Software Standardization of Data Formats – LAS file format Commercial Packages for Filtering and Editing 3D or Holographic Visualization Integration with photogrammetric systems Intelligent data thinning and feature extraction Efficient storage and access Data fusion

LiDAR Technical Challenges GPS/IMU – can it ever be perfect Detection of positional errors Adjustment techniques to correct for errors System Performance and Calibration LiDAR providers need to agree on objective measures of system performance Need to agree on methodologies to measure system performance Need to identify and model sources of systematic error

LiDAR Industry Challenges Guidelines and standards – what should they address –ASPRS Committee working on standards and practices including LAS data format - –FEMA guidelines and specifications, published February 2002 –

LiDAR Industry Challenges Product specifications – what is the correct metric for LiDAR elevation accuracy –Is error a normal distribution –Is error constant through out a particular data set

Questions? John Erickson Project Manager Ayres Associates 2445 Darwin Road Madison, WI Phone (608) Fax (608)