joel nelson quick poll – show of handsmvtl.com/_static/web/assets/media/pdf/2019lidar.pdf · u....
TRANSCRIPT
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Joel NelsonU. of Minnesota, Dept of Soil, Water, and Climate Quick Poll – Show of Hands
Who has heard of LiDAR
Who uses LiDAR data currently?
What is LiDAR?
Credit – ESRI
LiDAR
What is LiDAR?
• Light Detection And Ranging – a remote sensing system used to collect topographic data
• Produces high-resolution, accurate, land-surface information
• Elevation data
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Elevation Data FormatsModels of Topography
Multiple ways of representing elevation
○ Triangulated irregular network
○ Contours (Vector)
○ Digital elevation model (Raster)
Credit – Steve Kloiber- MNDNR
Each has advantages and disadvantages
DEM is used most often for terrain analysis and watershed delineation
Digital Elevation Model (DEM)
What is a DEM?• Digital file that:
• Contains elevation of terrain over a specified area
• Is arranged as a fixed-grid interval over the earth surface
• Is geo-referenced
• Can be manipulated to create other elevation-dependentdata products
DEM ComparisonUSGS 30m DEM
NOAA - https://coast.noaa.gov/digitalcoast/training/intro-lidar.html
DEM ComparisonUSGS 10m DEM
NOAA - https://coast.noaa.gov/digitalcoast/training/intro-lidar.html
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DEM ComparisonLiDAR‐Derived DEM
NOAA - https://coast.noaa.gov/digitalcoast/training/intro-lidar.html
DEM ComparisonWhy does it matter?
NOAA - https://coast.noaa.gov/digitalcoast/training/intro-lidar.html
Effect of Cell Size - Resolution
NOAA - https://coast.noaa.gov/digitalcoast/training/intro-lidar.html
DEM Resolution Tradeoff Lower resolution = faster processing
Higher resolution = more precision, maintains small features
Coarse to Fine
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LiDAR Systems
Credit – ESRI
Deploying LiDAR
NOAA - https://coast.noaa.gov/digitalcoast/training/intro-lidar.html
Fixed-position LiDAR
NOAA - https://coast.noaa.gov/digitalcoast/training/intro-lidar.html
Mobile LiDAR
NOAA - https://coast.noaa.gov/digitalcoast/training/intro-lidar.html
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LiDAR – Airborne SurveyHow is aerial LiDAR data collected?
Airborne survey:• Covers the surface with
multiple discrete laser pulses
• Early flights - up to 150,000 per second
• Current – 1 Million
• Collects the returnsTime = distance + GPS = Location
LiDAR Survey Equipment
Light Detection and Ranging
Laser Rangefinder - Scanner
IMU (INS)
GPS
On board computer
Produces accurate land elevation data
Credit - USGS
LiDAR Survey Equipment
On board computing equipment
Records data
○ Laser distance and intensity
○ IMU info
○ GPS info
Converts into
○ X, Y, Z
○ Millions of points
On-board display
Credit - USGS
LiDAR Data ResolutionBased on collection density
1 point/meter to 8 points/meter with ground control point validation – most basemapping
Supports 2 foot contours to sub 1-foot contours
New LiDAR– Geiger, Single Photon, and Flash Technologies –100 points/meter capable – sub pulses – higher densities
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LiDAR Representations
Point Cloud/LAS
Raster – DEM
Vector – Contours
Triangulated Irregular Network (TIN)
Terrain
Credit - USGS
LAS Files Source data for other products
Can be manipulated to represent elevation as well
LiDAR Data Validation
Vertical Accuracy QA/QC Purpose:
○ Data Validation – we got what we bought
○ Data Integrity – we want people to trust the data
Compare LiDAR elevations with Surveyed Points
○ 100 surveyed validation points per county
○ 20 points in each of 5 cover categories
○ Help from county surveyorsCredit – Tim Loesch - MNDNR
LiDAR Data Collection TerminologyLiDAR Returns: Multiple discrete return pulses
LiDAR Intensity: Magnitude or strength-of-return pulse
Metadata: Information about how data was collected—READ IT!
All returns can be used• Forest canopy• Intensity image• Vegetation mapping
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Returns
Single Return
Multiple returns
Waveform Returns
Credit - USGS
Returns
Single Return
Multiple returns
Waveform Returns
1st return
2nd return
3rd return
4th return
Credit - USGS
Returns
Single Return
Multiple returns
Waveform Returns
NOAA - https://coast.noaa.gov/digitalcoast/training/intro-lidar.htmlCredit - USGS
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Bare Earth vs. First Return
Credit – Grit May - IWI
Bare Earth vs. First ReturnTop: Digital Surface Model (DSM)Bottom: Digital Elevation Model (DEM)
Credit – Tim Loesch - MNDNR
LiDAR Status
Credit – ESRI
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LiDAR – Precision Ag. Applications
Credit – John Nowatski - NDSU
LiDAR – Precision Ag. Applications
• Hydrologic Modeling
• Topography - Inform Precision Management Decisions
• First Return – Plant height, spatial characteristics
Credit – John Nowatski - NDSU
LiDAR – Precision Ag. Applications
• Hydrologic Modeling
• Flood mitigation
• Tile Drainage
Photo credit: www.capecentralhigh.com
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Hydrologic Modeling
Identify appropriate water conveyance
Watersheds
Filled Sinks
LiDAR – Precision Ag. Applications
• Topo layer – inform precision management decisions
• Soil characteristics, water table, surface flow, solar radition, etc.
• Topographically controlled or affected
• Bare Earth –• Terrain attributes
Credit – John Nowatski - NDSU
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Terrain Analysis
Model real landscape processes
Utilize base layer DEM
Credit – Adam Birr – MN Department of Agriculture
Slope• Describes
overland and subsurface flow velocity and runoff rate.
• Slope quantifies the maximum rate of change in value from each cell to its neighbors.
Credit – www.inovativegis.com
Flow Accumulation
• Primary attribute representing the drainage area of any given cell
• Indicates overland flow paths
• Associated terms catchment area, upslope contributing area
Elevation
300 m
308 m
30
10,000
FlowAccumulation
Flow Accumulatio
nFlow Accumulation
Catchment Area orUpslope Contributing Area
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Stream Power Index
• Secondary attribute: product of Slope and Flow Accumulation
• Quantifies the potential erosive power of overland flow
• Isolates areas with large catchments and steep slopes
Ln (A * Slope) = Stream Power Index (SPI)
X =
High
Low
SPI
Stream Power Index
• Measure of the potential erosive power of overland flow
• Combines catchment area with slope
• Steep slope with large drainage areas result in a high value for SPI. Indicator of where
ephemeral gullies may form in a field
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CTI = Ln (A / S)
=
Terrain Attributes: Compound Topographic Index
Secondary attribute: divide flow accumulation by slope
Also referred to as the “Steady State Wetness Index” or “Wetness Index”
Identifies areas where water collects or ponds in a landscape
ln (A / Slope) = Compound Topographic Index (CTI)Upland Depressions
Critical Areas
Compound Topographic Index (CTI)
Measure of the potential wetness in any portion of the landscape
Combines catchment area with slope
Low slope and/or large catchment equal high potential for water to collect○ Indicator of potential
wetlands, different soil types
High CTI Value
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LiDAR – Precision Ag. Applications
• First Return –
• Plant Height – range
• Superior vs passive optical measurement
• Damage, condition, etc.
Credit – John Nowatski - NDSU
Image courtesy of © RIEGL LMS, www.riegl.com
Image courtesy of © RIEGL LMS, www.riegl.com
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LiDAR Download in MNMN TOPO