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Finding faults with LIDAR in the Puget Lowland Ralph Haugerud, Craig Weaver U. S. Geological Survey Jerry Harless Puget Sound Regional Council and thanks to TerraPoint LLC, Houston TX
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Why LIDAR? What is LIDAR? How are we doing LIDAR? What are we finding?
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30 km In some places, it is easy to see where the active faults are.
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In other places, it is not. 30 km Seattle Tacoma
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What are the salient differences? SF Bay area Puget Lowland slip rate 3 cm/yr strike slip 4 mm/yr shortening average tree height ? 10 ft? 100 ft age of landscape ~10 6 years 18,000 years
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18,000 yr 1 mm/yr = 18 m 10 6 yr 1 mm/yr = 1 km In the Puget Lowland, to see a fault with the same slip rate as in the SF Bay area, we have to look more closely. age slip rate = feature size
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LI ght D etection A nd R anging Airborne scanning laser rangefinder Differential GPS Inertial Navigation System 30,000 points per second at ~15 cm accuracy $400–$1000/mi 2, 10 6 points/mi 2, or 0.04–0.1 cents/point Extensive filtering to remove tree canopy (virtual defor- estation)
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10-meter DEM from contours
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12-ft DEM from LIDAR
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Picture: Oblique view of S end Rockaway Beach
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High-resolution LIDAR topography
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Fly in winter, when leaves are off Near-infrared laser; doesn’t penetrate clouds, rain Errors Largest are in angles—up to 1 m x-y error Ranging error = ~15 cm z error! 2/3 of surveyed points on trees and buildings; remove with automatic geometric filtering Multiple reflections from one laser pulse = better filtering
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Optimum working distance circa 1 km –Adequate reflection brightness –Keep laser eye-safe Spot diameter: decimeters to meters Spot spacing: 1 to 5 meters Multiple passes –multiple look angles –higher point density –internal consistency check $400 - $1,000 / mi 2
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Why is LIDAR better than photogrammetry? (It’s the trees) Suppose timber allows 1 of 3 arbitrary rays to reach ground; 1/3 of ground can be surveyed by LIDAR Photogrammetry requires 2 separate views of a point; only 1/9 of ground will be locatable
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Bainbridge Island, KPUD 1996-1997 Snoqualmie, USGS-NMD 1998-2001? Seattle Tacoma
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Puget Sound LIDAR Consortium ParticipantsExpertise Kitsap County Kitsap PUD City of Seattle Puget Sound Regional Council NASA USGS (exclusive of USGS) –Contracting –Surveyor –prior LIDAR experience –Geologist –GIS
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Puget Sound LIDAR Consortium No formal structure One agenda One contract Separate payments Share data Release all data to public domain (www.GetItYourselfBob, to be hosted by UW library)
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PSLC Tacoma Seattle
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Tacoma Seattle LIDAR already flown to be flown this Winter ~$3.3M ~$3M
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Toe Jam Hill fault scarp Waterman Point scarp beach uplifted during 900 AD earthquake 15 km west of Seattle
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landslides southern Bainbridge Island
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Uses for high-resolution topography Finding faults (earthquake frequency, kinematics) Geologic mapping Landslide hazards Flood hazards, groundwater infiltration, runoff modelling Fish habitat ?Precision forestry ?Noise propagation
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