2012 Lidar DEM: Fall Creek, OR

Fall Creek project area.

Create custom data files by choosing data area, product type, map projection, file format, datum, etc. A new metadata will be produced to reflect your request using this record as a base.

Bulk download of files in GeoTIFF format, in geographic coordinates, orthometric heights.

The Data Access Viewer (DAV) allows a user to search for and download elevation, imagery, and land cover data for the coastal U.S. and its territories. The data, hosted by the NOAA Office for Coastal Management, can be customized and requested for free download through a checkout interface. An email provides a link to the customized data, while the original data set is available through a link within the viewer.

This graphic displays the footprint for this lidar data set.

Link to the Data Report.

Link to custom download the lidar point data,from the Data Access Viewer (DAV), from which these raster Digital Elevation Model (DEM) data were created.

Acquisition.

This LiDAR survey utilized an Optech Orion mounted in a Cessna Caravan 208B aircraft. The LiDAR system was set to acquire ≥100,000 laser pulses per second (i.e., 100 kHz pulse rate) and flown at 800 m above ground level (AGL), capturing a scan angle of ±14o from nadir . The survey implemented opposing flight lines with side-lap of ≥50% (≥100% overlap) to reduce laser shadowing and increase surface laser painting. To solve for laser point position, an accurate description of aircraft position and attitude is vital. Aircraft position is described as x, y, and z and is measured twice per second (2 Hz) by an onboard differential GPS unit. Aircraft attitude is described as pitch, roll, and yaw (heading) and is measured 200 times per second (200 Hz) from an onboard inertial measurement unit (IMU).

Ground Survey

During the LiDAR survey, static (1 Hz recording frequency) ground surveys were conducted over set monuments. After the airborne survey, the static GPS data are processed using triangulation with Continuously Operating Reference Stations (CORS) and checked using the Online Positioning User Service (OPUS1) to quantify daily variance. Multiple sessions are processed over the same monument to confirm antenna height measurements and reported position accuracy. During every LiDAR survey, static (1 Hz recording frequency) ground surveys were conducted over either pre-existing or newly set monuments. After the airborne survey, the static GNSS data were processed using triangulation with Continuously Operating Reference Stations (CORS) and checked using the Online Positioning User Service (OPUS ) to quantify daily variance. Additionally, a daily RTK survey was conducted to collect ground control points. These data are then used in the processing of the LiDAR data acquired during the flight.

WSI owns and operates multiple sets of Trimble GPS and Global Navigation Satellite System (GNSS ) dual-frequency L1-L2 receivers used in both static and RTK surveys.

Existing and established survey benchmarks serve as control points during LiDAR acquisition. All monumentation established by WSI is set using 5/8” x 30" rebar topped with a 2” aluminum cap marked with the monument name, date and “WATERSHED SCIENCES INC., CONTROL” across the top.

Laser Point Processing

Laser point coordinates are computed using the LMS software suites based on independent data from the LiDAR system (pulse time, scan angle), and aircraft trajectory data (SBET). Laser point returns (first through fourth) are assigned an associated (x, y, and z) coordinate along with unique intensity values (0-255). The data are output into large LAS v. 1.2 files; each point maintains the corresponding scan angle, return number (echo), intensity, and x, y, and z (easting, northing, and elevation) information. The system allows up to four range measurements per pulse, and all discernible laser returns are processed for the output dataset. Flightlines and LiDAR data are then reviewed to ensure complete coverage of the project area and positional accuracy of the laser points.

Once the laser point data are imported into TerraScan, a manual calibration is performed to assess the system offsets for pitch, roll, heading and mirror scale. Using a geometric relationship developed by WSI, each of these offsets is resolved and corrected if necessary.

The LiDAR points are then filtered for noise, pits and birds by screening for absolute elevation limits, isolated points and height above ground. Supervision of point classes occurs, and spurious points are removed. For a *.las file containing approximately 7.5-9.0 million points, an average of 50-100 points are typically found to be artificially low or high.

Common sources of non-terrestrial returns are clouds, birds, vapor, and haze.

Internal calibration is refined using TerraMatch. Points from overlapping lines are tested for internal consistency and final adjustments are made for system misalignments (i.e., pitch, roll, heading offsets and mirror scale). Automated sensor attitude and scale corrections yield 3-5 cm improvements in the relative accuracy. Once the system misalignments are corrected, vertical GNSS drift is resolved and removed per flight line, yielding a slight improvement (<1 cm) in relative accuracy. In summary, the data completes a robust calibration designed to reduce inconsistencies from multiple sources (i.e., sensor attitude offsets, mirror scale, GNSS drift).

The TerraScan software suite is designed specifically for classifying near-ground points (Soininen, 2004). The processing sequence begins by ‘removing’ all points that are not ‘near’ the earth based on geometric constraints used to evaluate multi-return points. The resulting bare earth (ground) model is visually inspected and additional ground point modeling is performed in site-specific areas (over a 50-meter radius) to improve ground detail. This is only done in areas with known ground modeling deficiencies, such as: deeply incised stream banks and dense vegetation. In some cases, ground point classification includes known vegetation (e.g., understory, low/dense shrubs, etc.) and these points are then manually reclassified as non-grounds. Ground surface rasters are developed from triangulated irregular networks (TINs) of ground points.

The NOAA Office for Coastal Management (OCM) received 4 bare earth DEM files in Arc Grid format from DOGAMI. The data were in UTM Zone 10N, NAD83, meters, coordinates and NAVD88 (Geoid03) elevations in meters. The EPSG code (Vertical - 5703), was assigned. The data were converted to GeoTIFF format for ingest into the Digital Coast Data Access Viewer and to adhere to the Open Data Policy.