LIDAR and TDS in GIS A Comparison of Channel Geometry Profiles Created from Remotely Sensed and On-the-Ground Survey Data (or..how a programmer in China made life easy) By Jason S. Alexander Department of Aquatic, Watershed and Earth Resources Utah State University ?

Quick Map Purpose of research and analysis Data origins / advantages and disadvantages Methods of analysis Results Conclusions and Improvements

Location of Research Lodore Canyon, CO

Basic Purpose of Research Determine the effects of Flaming Gorge Dam and invasive riparian vegetation on channel planform

Basic Purpose of this Analysis Compare total station (TDS) survey data with remotely sensed (LIDAR) data Assuming TDS is the control we want to know the relative reliability of LIDAR for analysis of channel planform changes.

Data Origins - TDS Laser total station survey data of established permanent cross sections in experimental reaches of Lodore Canyon (May 2005)

Data Origins - TDS Precision of <2 cm within local grids (no real-world coordinates…yet)

Advantages - TDS Extreme accuracy and precision Low cost Can be coupled with sonar data Integrated research Allows for graduate students to leave their desk for extended periods

Disadvantages - TDS Generally in 2D (repeated profiles) Cumbersome and time consuming for 3D topography Requires large crews for efficiency Not in real world coordinates Risky (data and health)

Data Origins - LIDAR LIght Detection And Ranging (LIDAR) performed in experimental reaches of Lodore Canyon, April 2005

Data Origins - LIDAR Accuracy of ~15cm vertical and 1m horizontal

Advantages - LIDAR Data saturation (millions of points with 15cm vertical accuracy over large area) Can be coupled with high-resolution aerial photography Large scale volumetric analysis Minimal logistics, just money

Disadvantages - LIDAR Expensive (especially for repeats) 15 cm vertical accuracy means significant error in volumetric analysis and water surface elevation No sub-aqueous data Graduate students stay at their desk

Methods Translate and rotate local grids into real-world coordinates

Methods Translate and rotate local grids into real-world coordinates

Methods Create TIN from LIDAR survey points

Methods Create TIN from LIDAR survey points

Methods Cut profiles and export coordinates…easy?…NO!

Methods 3D Analyst does not (with standard tools) export XYZ coordinates from profiles!

Methods A search of the ESRI support center finds this is a common problem!

Methods Then came Min-Lang Huang! Author of the EZ Profiler….

Methods EZ Profiler V8.3 is an independent extension (does not need 3D analyst)!

Methods Profiles can be sampled at equal intervals or with set number of points

EZ Profiler Cross Section Point Shapefile Methods Shapefiles are created for each profile EZ Profiler Cross Section Point Shapefile

Methods Attributes include Northing, Easting, Elevation, and Distance

Attribute table “export to Excel” button Methods Attribute tables can be easily exported to Excel! Attribute table “export to Excel” button

Methods Then compared to TDS survey data!

Results General profile shapes are comparable, but…..

Results No specific patterns were found in the behavior of LIDAR vs. TDS

Results “Eyeballing” profiles works out, but what about the accuracy?

Results Spot checks reveal significant differences in elevations

Results Profile width also exhibits large variance

Results Water surface elevation data from LIDAR is not reliable

Improvements Use differential GPS to aquire real-world coordinates for local grids Ground surface at each LIDAR ground target EZ Profiler + “Snapping”

Conclusions TINs created from LIDAR provide equivalent or superior profile shapes Evaluation of accuracy is difficult (if not impossible) without improvements LIDAR data are unreliable for water surface elevation

Refs / Acknowledgments Min-Lang Huang : author of EZ Profiler software ! http://arcscripts.esri.com/details.asp?dbid=12685 Dr. Tarboton for assistance with TIN creation

Questions or Comments?