1. Using the SINK Hydrologic Function to Identify Treetops in Small-Footprint Multiple-Return Lidar Data Jason Stoker Lidar Remote Sensing Scientist USGS EROS Data Center Sioux Falls, SD Symposium on Terrain Analysis for Water Resources Applications December 16-18, 2002 University of Texas - Austin

2. What……….???? Do I care about? Trees? Trees? Lidar– OK Lidar– OK SINKs– OK SINKs– OK Results? Results?

3. Site Description Location of Cheesman Lake

4. The 15 ha Plot

5. Description of the Lidar Sensor 3Di Technologies of Boulder, CO3Di Technologies of Boulder, CO Small-footprint multiple-return systemSmall-footprint multiple-return system Up to five returns per pulseUp to five returns per pulse Intensity recorded for each returnIntensity recorded for each return Courtesy of 3Di Technologies

6. Description of the Lidar Sensor 3Di Technologies of Boulder, CO3Di Technologies of Boulder, CO Pulse rate of 36.5 kHzPulse rate of 36.5 kHz Fast retrace linear scan patternFast retrace linear scan pattern Posting density from 1m x 1m to 2.8m x 2.8mPosting density from 1m x 1m to 2.8m x 2.8m

7. Methods Freestanding, individual treesFreestanding, individual trees Separate freestanding trees from clumps of treesSeparate freestanding trees from clumps of trees Qualitative analysis of point cloudsQualitative analysis of point clouds Height, Length of Live Crown, DBH, and VolumeHeight, Length of Live Crown, DBH, and Volume Identify the number of overstory treesIdentify the number of overstory trees All overstory trees in 15 ha plotAll overstory trees in 15 ha plot Delineate tree crownsDelineate tree crowns Height, DBH, and VolumeHeight, DBH, and Volume

9. Veg Return- Bare Ground Return= Veg Returns on GRID GRID Flat Surface Who Needs Topography? - =

10. Freestanding Trees versus Clumps Freestanding Clumps

11. Identifying freestanding trees Vegetation-only contoursVegetation-only contours 3 meter contour3 meter contour Only one surveyed treeOnly one surveyed tree Clipped 1 st -5 th and BG returnsClipped 1 st -5 th and BG returns

12. Qualitative Analysis of Point Cloud Overlaid return points on TINsOverlaid return points on TINs Photograph treePhotograph tree GPS photo locationGPS photo location

13. Qualitative Analysis of Point Cloud

14. Identifying the number of trees in a clump Identify “treetops”Identify “treetops” Compare # of treetops per clump to surveyed trees per clumpCompare # of treetops per clump to surveyed trees per clump Use threshold method to raise barUse threshold method to raise bar Treetops

15. The SINK Hydrologic Function Creates a grid identifying all sinks, or areas of internal drainage (ESRI, Redlands, CA) Sinks are considered to have undefined Sinks are considered to have undefined flow directions flow directions Usually caused by errors in the data Usually caused by errors in the data

16. Sink

17. Identifying the number of trees in a clump Identify “treetops”Identify “treetops” Inverted vegetation only gridInverted vegetation only grid Used Hydrological GIS method to identify “sinks”Used Hydrological GIS method to identify “sinks” Sinks

18. Height Thresholds and the Wilcoxon Signed Rank Test Compared surveyed number to Lidar number in clumpCompared surveyed number to Lidar number in clump Many trees in understory- not detectableMany trees in understory- not detectable Wilcoxon- H 0 : Median of Differences = 0Wilcoxon- H 0 : Median of Differences = 0 Different Height thresholds to get into the overstoryDifferent Height thresholds to get into the overstory

20. Identifying the number of trees in a clump All surveyed trees

21. Identifying the number of trees in a clump Surveyed trees > 4 m

22. Identifying the number of trees in a clump Surveyed trees > 6 m

23. Identifying the number of trees in a clump Surveyed trees > 8 m

24. Identifying the number of trees in a clump Surveyed trees > 10 m

25. Identifying the number of trees in a clump Surveyed trees > 12 m

26. Number of trees in a Clump p < 0.0001 p =0.11 p = 0.007 p < 0.0001 p = 0.37 p = 0.83 p = 0.04 p = 0.0001 p < 0.0001 H 0 : Median of Differences = 0

27. Surveyed stem locations were not accurate enough to compare locations of treetops Can resolve only overstory trees Can resolve only overstory trees Next step- delineating individual overstory crowns Next step- delineating individual overstory crowns Useful for even aged / managed stands? Useful for even aged / managed stands? Further thoughts:

28. Acknowledgements David Box- 3Di Technologies, Inc. David Box- 3Di Technologies, Inc. Dr. Roger Hoffer- Colorado State University Dr. Roger Hoffer- Colorado State University Dr. Merrill Kaufmann- USFS Rocky Mountain Dr. Merrill Kaufmann- USFS Rocky Mountain Research Station Research Station Dr. Luis Garcia- Colorado State University Dr. Luis Garcia- Colorado State University