1LIDAR Seminar at OSU – Taylor Key Words / Summary Notes April 28, 2009 Speaker: Russell Faux from Watershed Sciences, Corvallis ([email protected]) LIDAR – Light Detection and Ranging Premise: Aerial survey of Earth’s surface using laser pulses, traveling at speed of light, from aircraft to ground surface and back. If aircraft position and 2-way travel time of laser pulses are known, land surface elevation and land cover can be derived. EM spectra – typically using near Infrared wavelengths Pulse rate: ~100 kHz = 100,000 laser pulses per second Point Density 2 / sq m to 8 per sq. m Key Concepts and Terms Land Classification Ground Point Cloud First Returns Last Returns Post-Processing Algorithms 1-m DEM; 10-m DEM Land Cover Model vs. Bare Earth Model Accuracy – position vs. correction 50% sidelap in flight lines = typical TIN = triangular irregular network (a grid model) Grid matrix Nadir – center point vertically below aircraft Higher altitude flights = less expensive (less data to process, longer pulse travel times) Lowe altitude flights = more expensive (more data to process, shorter pulse travel times) Data Correction: aircraft gyroscope, roll-pitch-yaw Leaf-on vs. Leaf-off data collection Leaf-off = more ground returns Oregon Lidar Consortium Puget Lidar Consortium Fog / Clouds absorb radiation, make flights difficult, effects point density and intensity (avoided) Lidar point density vs. Lidar intensity (strength of return pulses; absorption vs. reflection) Absorption reduces intensity; Black objects absorb, white reflect, Lidar does not penetrate water Flight planning factors: pulse density, flight line overlap, accuracy/position needs, flight time, air conditions, mobilization costs/location, GPS satellite schedule, GPS coverage quality Wing tipping – reduces reception, signal loss2Monitoring pulse returns and intensity to assess absorption, reflection; pulse rate, returns, point density Water < reflection Real-time swath monitoring and raw data visualization “returns” of pulses: percentage of initial signal Frequency = pulse rate per second Deliverables: GIS Maps/databases, DEMs, survey/engineering reports, raw ASCII x-y-z data files Ground elevation point data: x,y,z; raw vs. filtered LIDAR covers a lot of ground, more robust and accurate over larger areas compared to ground surveys Applications: Watersheds, geomorphology, landslide/fault detection, firs-return vegetation models, bare-earth models, vegetation rendering/modling, first-return models allow land cover classification, DEM-based hydrologic modeling John Day Basin example given modeling of woody debris, forest inventory, land change studies, mapping power lines, 3-D urban footprint models can fly at night Lidar types: discrete (typical), full wave form, ground based lidar, mobile lidar, “green lidar” for penetrating water and bathymetric mapping Cost: for Oregon Lidar Consortium, flying areas over 250,000 ac = $0.78 / ac; for small projects less than 60,000 ac, highly variable based on needs/conditions up to
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