2017 GIS in the Rockies presentation

1. Practical
Considerations
and Uses of
USGS 3DEP Lidar
John J. Kosovich
Lori Phillips
U.S. Geological Survey
jjkosovich@usgs.gov
September 21, 2017
GIS in the Rockies

2. Agenda
Brief lidar overview
Accessing 3DEP Products
Metadata, Services, Tools
Future expectations

3. Disclaimer
Any use of trade, product, or firm
names is for descriptive purposes
only and does not imply
endorsement by the U.S.
Government.

4. Lidar Terminology
“Linear” = traditional, where laser pulses are sent and returned in sequence. Can be
aerial-, tripod-, or satellite-based.
Discrete returns = Points from pulse where returned energy from waveform is greatest.
Multiple returns = each pulse may hit more than one object and continue down, resulting
in several discrete returns (points) per pulse.
Intensity = grayscale raster made from energy intensity of return points.
Terrestrial = tripod-based, close range, extremely dense (~1000s of points / m ).
Waveform = Entire pulse’s returned energy signature digitized, peaks typically become
the discrete points. Waveforms are not always saved unless required by customer.
Photon-counting = Latest technologies, single-photon (SPL), Geiger-mode (GM) lidar.
Point cloud = all returns from all pulses. Points located in X,Y,Z coordinate space.
Point density = nominal number of points per unit area (2D space, usually 1st
returns).
Point (pulse) spacing = nominal spacing between points (2D space, usually 1st
returns).
DSM = digital surface model, gridded raster, contains canopy, buildings, etc.
DTM = digital terrain model, gridded raster, bare-earth ground DEM.
2

5. Linear Lidar

6. From EarthData, Inc. original
• Lidar = light
detection and
ranging
• Active sensing: can
collect at night
• Cannot “see”
through typical cloud
cover
• Timing of returned
pulse gives elevation
• Magnitude of
returned pulse gives
intensity
• Minimum of
thousands of pulses
per second (KhZ+)
• Multiple returns
potentially from each
transmitted pulse
Lidar Collection

7. From EarthData, Inc. original
Multiple Returns per pulse
Multiple Returns

8. Lidar Digital Terrain Model
(DTM)

9. Lidar Digital Surface Model
(DSM)

10. Non-Lidar Image

11. Lidar Intensity –
All Returns

12. Lidar Intensity –
2nd Returns

13. Gridded Lidar DEMs (canopy height model and bare-earth ground) do not contain true 3D structure,
but the point cloud does:
Gridded Lidar DEMs (canopy height model and bare-earth ground) do not contain true 3D structure,
but the point cloud does:
Why Use Point Cloud?
Lidar digital surface model (DSM) =
Canopy Height Model (CHM)
for forested areas
Lidar point cloud
Lidar digital terrain model (DTM) =
bare-earth ground surface

14. X-band IfSAR
Typical lidar:
topo ~1064 nm,
bathy ~400 - 532 nm
Electromagnetic Spectrum
P-band IfSAR
EM spectrum image from Intermap Technologies, Inc. original

15. 3DEP
(3D Elevation Program)
Products

16. 3DEP Lidar Deliverables
Required by USGS Lidar Base Spec v1.2 (2014):
http://pubs.usgs.gov/tm/11b4/
Quality Level 2 or better (0.7m spacing, 2 pts/m )
Classified Point Cloud (tiled .LAS as per project,
includes intensity values for each return)
Bare-Earth Surface DEM (= DTM, 32-bit raster format)
Breaklines used in hydro-flattening (ESRI vector)
Metadata (FGDC-compliant)
2

17. Classified Point Cloud

18. Point Cloud Classes
Required by USGS Lidar Base Specification 1.2 (pg. 11)

19. Point Cloud Classes
ASPRS LAS Specification, Version 1.4 – R13, July 15, 2013, pg. 17
http://www.asprs.org/a/society/committees/standards/LAS_1_4_r13.pdf

20. 3DEP Products
http://nationalmap.gov/3DEP

21. 3DEP Products
~10m
~30m
~60m
Horizontal Coord System = UTM (CONUS) except superseded 1/9, Albers for AK
Horizontal Coord System = Geographic decimal degrees

22. DEM Horizontal Resolution
10m
2m
30m
1m
Photo by John Kosovich,
USGS

23. 3DEP Products
Note that Intensity images are not available, but can be user-derived from LPC.

24. 3DEP Product Availability
http://nationalmap.gov/3DEP

25. 3DEP Product Availability
http://nationalmap.gov/3DEP/3dep_prodavailability.html#/

26. 3DEP Product Availability

27. 3DEP Product Currency

28. 3DEP Product Quality Level

29. 3DEP Quality Level (QL)
Point density = nominal number of points per unit area (pts/m ).
Point (pulse) spacing = nominal spacing between points (m).
2
point density =
1
(point spacing)
2
point spacing =
1
point density
0 1m 2
QL1: 8 pts/m density
0.35m spacing
2
0 1m 2
QL2: 2 pts/m density
0.7m spacing
2
0 1m 2
QL3: 0.5 pts/m density
1.4m spacing
2

30. Seamless DEM Availability
~10m
~30m
~60m

31. Seamless Production Method

32. 10m DEM

33. 1m Lidar DEM

34. Seamless Currency by Year

35. Alaska IFSAR DTM Availability

36. Alaska Recent Updates

37. IfSAR 5m DTM

38. IfSAR 5m DSM

39. IfSAR ORI

40. 3DEP Product Download
http://nationalmap.gov/3DEP

41. Elevation Products
3DEP Download

42. Elevation Source Data
3DEP Download
LPC

43. Help
3DEP Download

44. 3DEP
Metadata

45. 3DEP Metadata
Spatial Metadata (Shapefiles)
 Seamless
 Project Extent (1 meter, OPR, LPC, DSM and ORI)
 Tile Extent (LPC, DSM and ORI only)
 Data Dictionary
Textual Metadata (FGDC)
 XML, HTML, TXT
Project Level
 Delivered as a separate download (.zip) with LPC

46. 3DEP Metadata
 Spatial Metadata for a Seamless DEM 1-degree block is part of
data download package.
 Spatial Metadata Data Dictionary:
https://nationalmap.gov/3DEP/documents/Data_dictionary_%2020160115.pdf

47. 3DEP
Services
and Tools

48. Services & Tools
https://viewer.nationalmap.gov

49. Evaluating
Latest Lidar
Technologies

50. Geiger-Mode (GML)
TM
Courtesy of Harris Corporation
http://asprs.org/a/publications/proceedings/IGTF2015/5H[4]-slides.pdf
Geiger-Mode Lidar
- Harris Corporation developed IntelliEarth sensor (Palmer scanner).
- 1064nm IR (topographic) full laser pulses produce elliptical sweep over flight line.
- Receiver consists of 32 x 128 array of photon-counting detectors (= 4096 total),
x 50,000 laser flashes / second = ~205 million measurements / second.
- Sensor samples same ground area multiple times, target hits are post-processed from
many aggregated returns from multiple flight lines (no time stamps on final points).
- Multi-angle illumination of target area.
- Lower power laser, higher flying height than linear mode lidar.
- Pseudo-reflectance image post-processed from how many times a target is hit by laser
(~ similar to intensity image from “linear” lidar).

51. Single Photon (SPL)
Courtesy of Leica Geosystems. and LaserFocusWorld
http://www.laserfocusworld.com/articles/print/volume-47/issue-9/world-news/lidar-photon-counting-3d-imaging-lidar-measures-biomass-and-the-cryosphere.html
Single Photon Counting Lidar
- Sigma Space Corp. (now part of Leica Geosystems) developed SPL-100 scanner.
- 532nm green laser, transmitted pulses are diffracted into 10 x 10 beamlets.
- Receiver array can detect ~single photons, receiver counts photos per array detector.
- Topographic and bathymetric collection.
- Lower power laser, higher flying height than linear mode lidar.
- Reflectance image made from photon count per pixel, ~ similar to intensity image
from “linear” lidar.

52. Questions?