Understanding LIDAR Technology Brian Mayfield, CP, GISP, GLS Timothy A. Blak, GS, PLS, CFM

Brief Introductions vBrian Mayfield, CP, GISP, GLS  Dewberry Program Manager to VGIN vTim Blak, GS, PLS, CFM  Appendix A of the Map Modernization Guidelines (  NDEP (National Digital Elevation Program) Guidelines for Digital Elevations Data ( lines_Ver1_10May2004.pdf) lines_Ver1_10May2004.pdf

Our Role in the Industry vTrusted Advisor  North Carolina  Maryland vMapping Solutions Provider  USGS GPSC  NOAA CSC  FEMA Regional IDIQ Study Contractor vNot a Mapping Firm  No Acquisition Resources (not tied to any specific technologies or brands) vIndustry Leading QA/QC Services  NOAA  Statewides

What is LIDAR vLIght Detection And Ranging vActive Sensing System  Uses its own energy source vMeasures range distances  Based on time between emission, reflection and receive time vDirect terrain measurements, unlike photogrammetry which is inferred vDay or night operation except when coupled with digital camera vLiDAR provides a point cloud with X.Y,Z positions

What LIDAR is NOT vAll-weather  Target must be visible within the selected EM spectrum  No rain or fog  Must be below clouds vAble to “penetrate vegetation”  LIDAR can penetrate openings in the vegetation cover but cannot see through closed canopies

Animation

LIDAR Components vThree major components of a LIDAR system 1.GPS 2.Inertial Measurement Unit 3.Laser Range Finder

Laser Returns vFirst  Ideal for surface models vLast  Ideal for generating bare-earth terrain models vIntermediate  Ideal for determining vegetation structure

Laser Returns Courtesy of EarthData Technologies

LIDAR data points - X, Y, Z Top View Side View Courtesy of Terrapoint

Intensity Images vMeasures the amount of light returning to the sensor vDeveloping technology – infancy stage vCan now be used for stereo-compilation to generate 3D breaklines (“LIDARgrammetry)

Intensity Imagery

Full Point Cloud Surface Model

Surface Model

Cityscape Surface Model

Cityscape Ground Model

Full Point Cloud Surface Model

LIDAR Uses Courtesy of Terrapoint

LIDAR Uses

Accuracy Standards vFEMA – Guidelines and Specification for Flood Hazard Mapping Partners Appendix A: Guidance for Aerial Mapping and Surveying vNDEP Guidelines For Digital Elevation Data

FEMA’s Criteria for Topographic Data For either photogrammetry or LIDAR: vAccuracy equivalent to 2’ contours or better for flat terrain (Accuracy z = 1.2’ at 95% confidence level) vVertical accuracy at 95% confidence level = Accuracy z = x RMSEz vAccuracy equivalent to 4’ contours or better for rolling to hilly terrain (Accuracy z = 2.4’ at 95% conf level)

Accuracy Equivalencies NMAS Contour Interval NMAS 90% Conf NSSDA 95% Conf NSSDA RMSE z 2’1’1.2’0.6’ 18.5 cm 4’2’2.4’1.2’ 37.0 cm

Quantitative Verification NDEP Standards as of Jan Fundamental Vertical Accuracy. For open terrain only, compute RMSE z. Report Accuracy z as: “Tested __ (meters, feet) Fundamental Vertical Accuracy at 95% confidence level in open terrain based on RMSE z x ” Supplemental Vertical Accuracy. For all other land cover categories, determine 95th percentile error(s). Report Accuracy z as: “Tested __ (meters, feet) Supplemental Vertical Accuracy at 95 th percentile in weeds, crops, scrub, forests, urban areas, etc.” and document outliers. AND/OR Consolidated Vertical Accuracy. Report Accuracy z as: “Tested __ (meters, feet) Consolidated Vertical Accuracy at 95 th percentile in open terrain, weeds, crops, scrub, forests, urban areas, etc.” and document outliers.

Contours vOnce the elevation model is created - contours are just a click away…or are they? vThe key to creating good contours is to control their behavior vControlling their behavior can be expensive using traditional methods vNew methodologies are being developed for LIDAR such as hydro-enforced contours or by “LIDARgrammetry”

Contours Two Types of Contours 1.Engineering 2.Topographic

LIDAR Contours

Breaklines vLinear features that control surface behavior vCan be 2D or 3D vTraditionally derived from stereo photogrammetry or from surveys vCan use LIDAR and Intensity to create breaklines or can use Hydro-enforced method

Pricing

Questions?