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Transcript of LiDAR 101
mplification by the
Acronyms will be flying around the room!!
Forest Service's free LiDAR software
Identify plant communities and/or individual species?
Hazard / change detection
Multi-spectral imagery fusion
by Tyson L. Swetnam, University of Arizona
Image: Robert McGaughey, USFS PNWRS
credit: Beland et al. 2015
Sensors 2011, 11(1), 32-53; doi:10.3390/s110100032
Image source: NCALM
Image source: Fianium Ltd
Hyper-spectral LiDAR (Supercontinuum Lasers)
Image source: The Verge
Google Project Tango
Where is the technology headed?
Species discrimination via passive hyperspectral cameras
Species discrimination via active hyperspectral laser
What you will learn
Describe how LiDAR is collected
Distinguish between different LiDAR products
What you get when you collect/order data
Find out where the technology headed
Tentative title for Thursday: "
Dr. Strangedata or: How I learned to stop worrying and love point clouds"
What is 3DEP?
Linear-mode vs Single-Photon and Geiger-mode
TLS vs UAV vs ALS: what should you use?
Why you should use (or at least know) open-source software
Prep for lab:
pre-installation of software: https://pods.iplantcollaborative.org/wiki/display/~tyson_swetnam/LiDAR+Lab
Read suggested material
• LAS –
format supports the exchange by 3-dimensional x,y,z tuplet.
• RMSE –
abbreviation for 'root mean square error'; measure of the accuracy of the data similar to the measure of standard deviation if there is no bias in the data.
• Accuracy_z, Fundamental Vertical Accuracy (FVA)
– a measure of the accuracy of the data in open areas at a high level of confidence (95%); calculated from the RMSE using the formula RMSE x 1.96 = FVA.
• Classification –
data that have been processed to define the type of object that the pulses have reflected off; can be as simple as unclassified (i.e., object not defined) to buildings and high vegetation. The most common is to classify the data set for points
that are considered “bare earth” and those that are not (unclassified).
• Returns –
first, second, third, and ultimately the “last” return from a single laser pulse, can help determine what the reflected pulse is (e.g., ground, vegetation).
• Point Spacing –
also called “posting density” or “nominal point spacing.”
• Pulse Rate –
per second the lidar instrument is firing. Systems now exceed 1 Mhz (million pulses / sec).
• Intensity –
object reflected wavelength of light used by the laser system
• RTK GPS (Real Time Kinematic GPS) –
satellite navigation that transmits Global Positioning System (GPS) signal at much higher frequency than standard units - resulting in more precise survey.
• DEM or 'Digital Elevation Model'
– a surface created from ground points data to represent the topography.
DSM or 'Digital Surface Model -
a surface created from the high hit point data to represent the actual surface including vegetation.
CHM or 'Canopy Height Model',
CHM = DSM - DEM, represents the object heights above ground height
Multi-spectral and Hyperspectral imagery
Remote Sensing 2012, 4(11), 3462-3480; doi:10.3390/rs4113462
example from a savannah ecosystem in S. Africa (Colgan et al. 2012) - flown with the NEON prototype hyperspectral camera.
Image source: NEON
Ensure quality data are collected!
Follow best practices for each given technology.
Read the literature (see end of this talk)
New systems are much faster than older technology - however, vendors still sell the same point density while reducing their costs
Understand ALS has large uncertainty relative to TLS (e.g. 10cm RMSEz vs 5-8 mm RMSE)
Ensure data are collected with 100% overlap, or 50% sidelap.
Overlap and Withheld points are classified in the cloud.
Density is high enough for your application
e.g. USGS QL1 = 8-12 ppsm
Ensure 100% illumination of your target area.
If you're collecting in plots, consider a central 360 degree scan, and 3 outer scans at 120 degree angles looking inward
Get up - find ways to elevate above your target
Find a high point (building, hilltop)
Rent a scissor lift
Don't buy a drone!
Position enough targets in the area to move your sensor multiple times.
Sensor needs at least 3 targets to reference multiple scans
What do you get?
Points, billions of points!
What do you do with them?
First optical LASER is developed mid- to late 1950s
First airborne laser ranging tried at that time!
Development ongoing through 1970s, including hydrographic and bathymetry application
Accurate GPS become availalbe in the 1980s
Professor Ackerman ("The Pope") and laser profiles in the mid-to late 1990s
Late 1990s GPS and IMU combind to make first ALS scanners (Linear-mode)
2004 Waveform digitiziation
2000s Military-use of Geiger-mode and Single Photon counting
2006 double scanners
2015 Geiger-mode announced for public
Ackermann, F. 1999. Airborne laser scanning—present status and future expectations. In ISPRS, 1999 pp. 64-67.
Baltsavias, E.P. 1999. Airborne laser scanning: existing systems and firms and other resources. In ISPRS, 1999 pp.
(Hint: this is what we'll do in lab)
Lecture 2 - What you'll learn
What is the near future of LiDAR?
Technological leaps (Geiger, Single Photon, Flash)
LiDAR Base Specifications
Where to find LiDAR data
What to do with the data after you've got it
Useful tools for viewing, editing, working with data
How to make derivative products which you can look at, analyze, serve to your customers/users
Where is the technology headed
Linear-Mode is a mature technology
Well established in the vendor community
New features like smart swath tracking and multi-spectral lasers
Geiger-Mode and Single photon are new market tech
Potential to collect 10x larger area at a time
Flash LiDAR (Time of Flight Camera)
Small form factor
USGS Apples to Apples (Linear v Geiger v Single Photon)
Point density and relative accuracy of the two new sensors are adequate
non-vegetated surface accuracy is within USGS base spec
Performance is poor in leaf-on, best in leaf-off
USGS base spec needs to be updated for the new tech
3DEP - The 3D Elevation Program
USGS program to collect enhanced elevation data in the form of high-quality LiDAR over the coterminous USA.
8-10 Year acquisition period.
States are now being awarded grants for huge collections
USGS LiDAR Base Specification v 1.2
Published in 2012, updated 2014
Established standards for LAS which meet the 3DEP
4 Quality Levels (QL)
Where to find LiDAR Data
Just a few examples
Pima County GIS - FTP Server, Data viewer
University of Arizona Library + Spatial Data Portal Viewer
OpenTopography - DEM and LiDAR Data
National Elevation Dataset (NED) USGS - Maps, GIS, Apps, Data
What to do with the data now that you've got it?
Ideally, you should run your OS from one hard drive, store your raw data on second drive, and write your output data to a third drive.
SSDs are your friend
Backup your data on the Cloud
UA provides you free, unlimited Google.Drive
You decide on your favorite GIS work environment - there are plenty of tools out there to consume LiDAR
Viewing the data
Public Header Block
point counts, data boundary
Point Data Record Format (PDRF)
Well Known Text (WKT) encoding of Coordinate Reference System (CRS)
No longer GeoTIFF
Variable Length Record (VLR)
waveform packet info
user app data
limited in size to 64 kb
Extended Variable Length Record (EVLR)
appended at the end of file to allow editing
can be any size
What to expect in a delivery dataset
Find the Vendor Report!
SBET (smoothed best estimate trajectories)
Hosting and providing data