Analysis of Terrain Evolution using Lidar data and open source GIS

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Analysis of Terrain Evolution using Lidar data
and open source GIS H. Mitasova, M.Overton, J.J.
Recalde North Carolina State University Raleigh,
USA R.S. Harmon Army Research Lab., Army Research
Office Research Triangle Park, Durham, USA
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Workflow for Terrain Modeling and Change Analysis
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GRASS6 open source GIShttp//grass.itc.it

• 1984 started at CERL as land management system
• 1999 GPL, all common OS, 32/64bit, code in C
• Web-based infrastructure for managing the code

• fully integrated 350 modules
• add-ons managed on wiki
• raster map algebra, DEM analysis, flow, buffers,
  solar,
• image rectification, multispectral,reclassificati
  on
• vector buffers, overlays, networks,
• DBMS attribute management, SQL
• transformations projections, raster-vector,
  interpolation
• visualization 2D, 3D visualization, ps maps
• WMS support, Google earth through v.out.ogr

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North Carolina Lidar Surveys
2005 USACE Topo/Bathy Mapping after hurricane
Ophelia SHOALS-1000T hydrographic (1pt/5m) and
topographic lidar 2004 USACE Topo/Bathy Mapping
SHOALS-1000T 2003, June, Sept. 18, 21 NASA/USGS
EAARL, acquired just before and after the
hurricane Isabel landfall 2001 NC Floodplain
Mapping survey, Leica Geoscan 1996-2000
USGS/NASA/NOAA ATM II published vertical
accuracy is between 15cm - 30cm
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Evolving coastal landscape Jockey's Ridge sand
dunes
2001 DEM (20ft resolution) based on NC Floodplain
lidar survey
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Photogr. 1974, 95, 98 Lidar 1999
Lidar 2001 RTK-GPS 2004
N
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Terrain Change Analysis
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Tuning the level of detail for feature extraction
RST tension and smoothing is used to create
surface at a desired level of detail while
keeping the 1m res.
tension 700
tension 100
profile curvature slope
road
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Feature extraction and change analysis
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1974 108 ft. 2001 72 ft.
rate of horizontal migration
The main dune rotates clockwise while its peak
moves southeast. Volume and area are relatively
stable
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2001
1974
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Dune field evolution 1974-2001
Relocation of leading south dune that was moving
out of park boundaries more surveys are needed
to understand whether the management is working
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Working with lidar data from a diverse set of
surveys
Oregon inlet
avg. no. of points per 2m res. grid cell 1996
0.2 ATM 1997 0.9 ATMII 1998 0.4 ATMII 1999
1.4 ATMII 2001 0.2 NCflood 2003 2.0
EAARL 2004 15.0 SHOALS 2005 6.0 SHOALS
Major overwash area used for testing 0.3m res.
2004 DEM
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Increasing LIDAR point density
substantially improved representation of
structures but much larger data sets
1m resolution DEM computed by RST
binned
computed by RST 2004 lidar 0.5m resolution DEM
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Mapping LIDAR point density
pt / 2m grid cell
2001 NC Flood
2004 SHOALS
Point density maps created by binning draped over
2m res DEM (2001) are used to select common
resolution
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Shifts in Lidar Surveys
Boxplot elevation differences between the most
accurate 2004 DEM and other surveys computed
along 1m wide road centerline strip most
surveys are shifted 10-20cm above or below road
elevation difference m
1996 1997 1998 1999a 1999b
1999c 2001 2003a 2003b 2005
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Impact of shifts in Lidar data
Do we have high erosion rate? Is the road
sinking?
original blue 1999 black 2001 A erosion 12m B
accretion 2m corrected red 1999 violet
2001 A erosion 4m (!) B accretion 8m
A
elevation difference m
B
1996 1997 1998 1999a 99b 99c
2001 2003a 03b 2005
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Analysis of systematic error
Elevation difference between RTK-GPS survey
(0.03m RMSE) and lidar data along centerline of
a stable road.
RTK-GPS 2001 lidar mean diff -0.23m
elevation m
0 0.7 1.3 2.0
2.6 3.2
distance km
RTK-GPS 2004 lidar mean diff -0.06m
Elevation difference between 2001 and 2004
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Conclusions

• - analysis of points density and systematic
  error
• is essential when using lidar for assessment
  of
• topographic change from multiple sources
• automated tracking of extracted features is
  needed
• for more efficient measurement of change
• - open source geospatial software provides
  powerful,
• customizable tools for analysis of terrain
  change
• OSGEO foundation supports the development of
  open
• source geospatial software and promotes its
  use.

First Joint Meeting 9/2006, Lausanne, CHgt
FOSS4G2006 Conference http//www.foss4g2006.org
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Acknowledgment
Funding by US Army Research Office, NC WRRI and
North Carolina Sediment Control Commission is
gratefully acknowledged We also thank
Geodynamics for performing the accurate road
survey.
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Communities growing together
GRASS GISSpatial Computing http//grass.itc.i
t
GDAL - Geospatial Data Abstraction Library
http//www.gdal.org
... AND MANY OTHERS!
http//www.osgeo.org
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Accuracy of approximated DEMs
RMSE of interpolated DEMs, based on 50pts
measured on pavements using RTK-GPS 0.25m
(1995) and 0.03m (lidar 1999, 2001)
Lidar 1999, first return data spatial
distribution of deviations
Surface deviation from the given points as
function of tension
vegetation
spatial distribution of vegetation
all
sand