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Airborne Lidar Processing System (ALPS) Workshop
A workshop on the Airborne Lidar Processing System (ALPS) was held February 12-15, 2008, at the U.S. Geological Survey (USGS)'s Florida Integrated Science Center (FISC) office in St. Petersburg. Led by Jamie Bonisteel (Jacobs Technology contractor at the USGS), the workshop's primary objective was to educate attendees on how to use the ALPS software to explore and process lidar (light detection and ranging) data and imagery acquired by Experimental Advanced Airborne Research Lidar (EAARL). EAARL is an airplane-mounted lidar system used to survey both onshore and nearshore topographic features, such as coral reefs, nearshore benthic habitats, coastal vegetation, and sandy beaches. ALPS is a custom-built system for postflight processing of EAARL data. Bonisteel revised the original ALPS manual—which was written by Amar Nayegandhi (Jacobs Technology/USGS), John Brock, (USGS), and C. Wayne Wright (National Aeronautics and Space Administration [NASA])—to include updates to the software, as well as tools for the software that were not in the original manual. EAARL is an example of a lidar system that uses light of a blue-green wavelength (532 nm) to determine the distance to an object. The distance is resolved by recording the travel time of a transmitted pulse at the speed of light. The system measures submerged topography and adjacent coastal-land elevations simultaneously by using raster-laser scanning with full-waveform (multipeak) resolving capabilities. (A raster-laser uses two suspended mirror assemblies, one mounted perpendicular to the other, to sweep the laser beam back and forth over a line in two dimensions.) The ALPS software, created by using open-source programming software operated on a Linux platform, enables the exploration and processing of EAARL data in either interactive mode (working with one file) or batch mode (working with multiple files). ALPS also allows for the creation of digital-elevation models (DEMs) of bare-earth (elevation of ground surface beneath vegetation), canopy-top (elevation of top of vegetation), and submerged (elevation of seabed) topography. The EAARL system uses an Earth-centered coordinate and reference system, which eliminates the need to reference submerged-topography data relative to water level or tide gauges. The workshop provided hands-on training for attendees, allowing interaction with modules developed for lidar-raster and waveform investigation and digital-camera-image playback. The class covered processing workflow—the series of steps involved in converting raw lidar data to DEMs that represent submerged, bare-earth, or canopy topography—including tools to filter and edit data either manually or in an automated way. The training class also provided an opportunity for users to become more familiar with the EAARL lidar waveforms and to explore the use of these waveforms in various scientific, monitoring, and inventory activities. Throughout the weeklong course, attendees learned how to load EAARL mission-day and ancillary data; browse lidar waveforms, red-green-blue (RGB)/color-infrared (CIR) images, and flight lines concurrently; process and analyze flight-line segments; determine the roll bias (effect of the plane's motion on the data); prepare data for batch mode; perform batch processing; process data for submerged topography (bathymetry); define bathymetry parameters; apply a random-consensus filter (RCF), iterative random-consensus filter (IRCF), and batch filter; perform manual editing; apply batch datum conversions; use manual editing tools; and, finally, create DEMs by using ALPS and GlobalMapper.
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in this issue:
New Method to Estimate Sea-Ice Thickness
Bill Normark: Ascent of Sea Cliff Bill Normark: Pisces Dive P5-78 St. Petersburg Office Dedicates New Building USGS Deputy Director Addresses Downtown Partnership
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U. S. Department of the Interior | U.S. Geological Survey
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