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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