2007 OPR Lidar DEM: Honeyman Dunes, OR

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The data set boundary footprint.

Data collector's website

Airborne Survey

The LiDAR survey utilized an Optech 3100 LiDAR laser system mounted in Cessna Caravan 208. The survey was conducted March 13, 2007. The Optech 3100 system was set to acquire 71,000 laser pulses per second (i.e. 71kHz pulse rate) and flown at 1000 meters above ground level (AGL), capturing a scan angle of ±15o from nadir1. These settings yielded points with an average native density of >6 points per square meter. The native pulse density is the number of pulses emitted by the LiDAR system from the aircraft. Some types of surfaces (i.e., dense vegetation or water) may return fewer pulses than the laser originally emitted. Therefore, the delivered density can be less than the native density and lightly variable according to distributions of terrain, land cover and water bodies.

The entire area was surveyed with opposing flight line side-lap of ≥50% (≥100% overlap) to reduce laser shadowing and increase surface laser painting. The system allows up to four range measurements per pulse, and all discernable laser returns were processed for the output dataset. To solve for laser point position, it is vital to have an accurate description of aircraft position and attitude. Aircraft position is described as x, y and z and measured twice per second (2 Hz) by an onboard differential GPS unit. Aircraft attitude is measured 200 times per second (200 Hz) as pitch, roll and yaw (heading) from an onboard inertial measurement unit (IMU).

Ground Survey

During the LiDAR survey, multiple static (1 Hz recording frequency) ground surveys are conducted over monuments with known coordinates. After the airborne survey the static GPS data are processed using triangulation with CORS stations and checked against the Online Positioning User Service (OPUS2) to quantify daily variance. Multiple sessions are processed over the same monument to confirm antenna height measurements and reported position accuracy. Thales Z-max DGPS unit is used for the ground real-time kinematic (RTK) portion of the survey. To collect accurate ground surveyed points, a GPS base unit is set up over monuments to broadcast a kinematic correction to a roving GPS unit. The ground crew uses a roving unit to receive radio-relayed kinematic corrected positions from the base unit. This method is referred to as real-time kinematic (RTK) surveying and allows precise location measurement (σ ≤ 1.5 cm ~ 0.6 in). 301 RTK ground points were collected in the study area.

Processing

1. Resolve kinematic corrections for aircraft position data using kinematic aircraft GPS and static ground GPS data. Software: REALM

2. Develop a smoothed best estimate of trajectory (SBET) file that blends the postprocessed aircraft position with attitude data. Sensor head position and attitude are calculated throughout the survey. The SBET data are used extensively for laser point processing. Software: POSPAC, POSGPS

3. Calculate laser point position by associating the SBET position to each laser point return time, scan angle, intensity, etc. Creates raw laser point cloud data for the entire survey in *.las (ASPRS v1.1) format. Software: REALM

4. Import raw laser points into manageable blocks (less than 500 MB) to perform manual relative accuracy calibration and filter for pits/birds. Ground points are then classified for individual flight lines (to be used for relative accuracy testing and calibration). Software: TerraScan v.6.009

5. Using ground classified points per each flight line, the relative accuracy is tested. Automated line-to-line calibrations are then performed for system attitude parameters (pitch, roll, heading), mirror flex (scale) and GPS/IMU drift. Calibrations are performed on ground classified points from paired flight lines. Every flight line is used for relative accuracy calibration. Software: TerraMatch v.6.009

6. Position and attitude data are imported. Data are classified as ground and non-ground points. Statistical absolute accuracy is assessed via direct comparisons of laser points to ground RTK survey data. Data are then converted to orthometric elevations (NAVD88) by applying a Geoid03 correction. Ground models are created as a triangulated surface and exported as ArcInfo ASCII grids. Highest Hit model surfaces are developed from all points and exported as ArcInfo ASCII grids. Intensity images (GeoTIFF format) are created with averages of the laser footprint. Software: TerraScan v.6.009, ArcMap v9.1

7. The bin-delineated LAS files (ASPRS v1.0) are converted to ASCII format, preserving x, y, z, and intensity fields. Software: TerraScan v.6.009

The NOAA Office for Coastal Management (OCM) received 1 digital elevation model (DEM) file in esri ArcGrid format from the Oregon Parks and Recreation Dept. The bare earth raster files was at a 1m grid spacing. The data were in UTM Zone 10 NAD83, meters coordinates and NAVD88 (Geoid03) elevations in meter. OCM assigned the appropriate EPSG codes (Horiz - 26910, Vert - 5703) and copied the raster file to https for Digital Coast storage and provisioning purposes. No metadata record was provided for this data set. This record was created by the NOAA Office for Coastal Management (OCM) using information from the data report.