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ALSM Data Collection Overview
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Acknowledgements

• NCALM
• Ken Hudnut (USGS)
• Mike Bevis (OSU)

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EarthScope
EarthScope is a bold undertaking to apply modern
observational, analytical and telecommunications
technologies to investigate the structure and
evolution of the North American continent and the
physical processes controlling earthquakes and
volcanic eruptions.

• Funded by NSF and conducted in partnership with
  the USGS and NASA
• EarthScope Facility
• Seismic observatory (USArray)
• The San Andreas Fault Observatory at Depth
  (SAFOD)
• Plate Boundary Observatory (PBO)

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GeoEarthScope

• Includes acquisition of aerial and satellite
  imagery and geochronology.
• Part of the EarthScope Facility project funded by
  NSF (MREFC).
• Managed at UNAVCO.
• Assist with EarthScope instrument siting.
• Examine strain field at different
  temporal/spatial scales than geodetic seismic
  instrumentation.
• Data will be freely available.

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UNAVCO

• UNAVCO is a membership-governed consortium that
  supports and promotes Earth science by advancing
  high-precision techniques for the measurement and
  understanding of deformation
• UNAVCO is funded by NSF and NASA
• UNAVCO Facility supports PI projects
• UNAVCO is constructing the EarthScope PBO
• UNAVCO manages GeoEarthScope
• UNAVCO hosts WInSAR
• UNAVCO is based in Boulder, CO, with five
  regional offices to construct PBO

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LiDAR and UNAVCO

• UNAVCO manages Airborne LiDAR (ALSM) acquisition
  projects for GeoEarthScope
• UNAVCO Facility provides GPS equipment and
  engineering support for Airborne LiDAR (ALSM)
  projects
• UNAVCO Facility acquiring pool of Tripod LiDAR
  (TLS) scanning instruments to support community
  projects

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• Airborne Laser Swath Mapping (ALSM)
• Data Collection

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Airborne Laser Swath Mapping (ALSM)

1. Laser scanner
2. Inertial Measurement Unit (IMU)
3. GPS

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Surface Point Spacing
User definable to provide necessary point pacing
on the surface
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ALSM and InSAR
Comparisons of Techniques for measuring surfaces
and detecting changes in surfaces
GPS InSAR ALSM TLS
Sample Density 1 site/10 km2 10,000 pixels/ km2 1-10 hits/ m2 1000 hits/ m2
Position Precision 1-20 mm 2-3 m 5-15 cm 0.6-5 cm
Change Detection 1 mm 1-2 cm 10 cm 1 cm
Scale Global 100 km 10-100 Km 1 km
Ball park numbers for typical applications
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ALSM Data Collection Parameters (NCALM)

• Aircraft Cessna 337 Skymaster
• Personnel
• One pilot, one operator in plane
• GPS ground crew (2 to 10 people)
• Scanner Optech near-IR
• PRF 33-125 KHz
• Flying height 600 1,000m AGL
• Flying speed 120 mph
• Swath overlap 50 nominal
• Ground truthing GPS (campaign CORS)
• Navigation solution KARS
• Point spacing sub-meter
• Nominal Accuracy (on open hard and flat surface)
• Vertical 3 6 cm.
• Horizontal 20 30 cm.

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Some ALSM Acquisition Issues

• Target identification and prioritization
• Defining collection scheme and data product
  requirements
• Tradeoffs concerning resolution vs. coverage
• GPS ground control requirements
• End use geomorphology, geodesy, etc.
• Cost (B4 500/sq.km., NoCal 400/sq.km., DV
  300/sq.km.)
• Will the data be useful to users 5 years from
  now?
• Seasonal constraints
• Leaf off, snow, heat, etc.
• Data volumelots of TBsyikes!
• Standard data products?
• Distribution scheme?

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Workflow

• Project planning
• Target I.D., LiDAR parameters, GPS parameters,
  flight lines, permits, etc.
• Data collection
• Flying and GPS deployments
• GPS data processing and trajectory generation
• Kinematic software (KARS, TRACK, etc.)
• LiDAR range processing and XYZ point cloud
  generation
• Proprietary software (at present)
• Filtered and unfiltered (e.g. full return and
  bare earth models)
• Surface generation
• Software (Surfer, Arc, GLW, etc.)
• Algorithms (tinning, kriging, etc.)

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ALSM Error Sources

• Position and orientation of aircraft (trajectory)
• IMU accuracy
• GPS accuracy
• absolute vs. relative reference frames
• GPS ground control points
• Laser pulse rate frequency (B4 70 KHz, NoCal
  70-125 KHz)
• Swath overlap
• Atmosphere (GPS water vapor, ionosphere, solar
  storms, etc.)
• Flying conditions due to wind, terrain, etc.
• Pilot skill
• Topography
• Dense / low-lying vegetation
• Processing methods
• Many more, many yet to be identifiednew field

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Corduroy
scan edge
SURFER 0.5 m DEM from NCALM - standard product
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Corduroy
There are two types of corduroy in B4 data
type 1 - scan angle artifact scanner reads
higher going one direction than it does in the
other type 2 - vertical swath offset
aircraft first pass is vertically mis-aligned
with second pass within a given area
The second type, at least, can be mitigated or
eliminated by increasing the accuracy of our
GPS/IMU trajectories
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Corduroy - type 1
Scan artifact - at scan edge on dry lake one sees
a pattern of up-down consistently as mirror
flips, height reads differently
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Corduroy - type 2
scan edge
The inner scan is consistently lower than the
outer scan this is a different source of
corduroy, the second type.
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GPS Positioning for ALSM
Bill Elliott, USGS Volunteer
Mike Sartori and the NCALM crew
1 Hz GPS base station from UNAVCO pool
Surveying the B4 aircraft to determine the
relative positions of the GPS antenna, the LIDAR,
the IMU and the orientation of these vectors
relative to the axes of the aircract.
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( 5 m2)
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• Poor canopy penetration due to
• Dense vegetation (understory) and debris close
  to the ground esp. a problem in heavily logged
  areas.
• Solutions
• Shorter pulse length instrument (not likely due
  to eye hazard)
• Larger beam divergence (20 cm standard vs. 1 m)?
• More shots via higher-pulse rate instrument or
  increased overlap.

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Vegetation and Ground Returns at Mill Gulch
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Pt. Density
IDW DEM
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B4 Project Swath and GPS Points
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ENTIRE SAN ANDREAS HAS NOW BEEN IMAGED WITH HIGH
RESOLUTION ALSM! (B4 GEOEARTHSCOPE)
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Future GeoES LiDAR Projects

• Southern/eastern California
• Intermountain Seismic Belt
• Pacific Northwest
• Alaska