2006 USFS Lidar: Rogue River - Siskiyou National Forest - Ashland, OR

Dates of collection.

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Bulk download of lidar files in laz format, 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.

Data report

Acquisition.

The LiDAR survey utilized an Opetch ALTM 3100 mounted in the belly of a Cessna Grand Caravan 208B. The survey was conducted on July 1st-4th, 2006 (Julian Days 182-185). Quality control (QC) pre-mission flights were performed based on manufacturer’s specifications prior to the survey. The QC flight was conducted at the Ashland, Oregon Airport using known surveyed control points. The positional accuracy of the LiDAR (x, y, z) returns are checked against these known locations to verify the calibration and to report base accuracy.

Operational settings included:

Laser pulse repetition rate: 70 kHz

Operating altitude: 1100 m above ground level

Flight speed: 105 knots

Scan Angle: +/- 14 degrees from Nadir

Scan Pattern: Sawtooth

Laser Footprint diameter on ground: 30 cm

Number of returns per laser pulse: up to 4

Multi-swath pulse density: at least 7.5 pulses per square meter

Applications and work flow overview:

1. POSGPS: Monument static GPS data are processed with aircraft GPS data to resolve kinematic corrections.

2. POSProc: Aircraft attitude data are incorporated with post processed aircraft kinematic GPS data.

3. REALM: Laser point data are calculated for the entire survey in *.las format.

4. TerraScan: Data are imported, manually calibrated and filtered for pits/birds.

5. TerraMatch: Internal consistencies derived from GPS and IMU drift are measured and corrected.

6. TerraScan: Develop ground models, statistical accuracy assessments, Geoid03 application, projection changes and transformations.

Aircraft Kinematic GPS and IMU Data

LiDAR survey datasets are referenced to 1Hz static ground GPS that are set up prior to the LiDAR aircraft survey flight. While surveying, the aircraft collects 2Hz kinematic GPS data. The onboard inertial measurement unit (IMU) collects 200 Hz aircraft attitude data. POSGPS v. 4.2 is used to process the kinematic corrects for the aircraft. The static and kinematic GPS data are then post-processed after the survey to obtain accurate GPS solution and aircraft positions during times of the survey. POSProc v. 4.2 is used to develop a trajectory file that includes corrected aircraft position and attitude information. The trajectory data for the entire flight survey session is incorporated into a final trajectory file that contains accurate and continuous aircraft positions and attitudes.

Laser Point Processing

Laser point coordinates were computed using the REALM v. 3.5.2 software suite based on independent data from the LiDAR system (pulse time, scan angle), aircraft attitude, and aircraft position. Laser point returns (first through fourth) are assigned an associated (x, y, z) coordinate, along with unique intensity values (1-255). The data are output into one very large LAS v. 1.0 file format; each point has a corresponding scan angle, return number (echo), intensity, and x,y,z (easting, northing, and elevation) information. The initial laser point file is too large to process. To facilitate laser point processing, bins (polygons) were created to divide the dataset into manageable sizes (less than 500 MB and approximately 1 km2 each). Flight lines and LiDAR data were then reviewed to ensure complete coverage of the study area and positional accuracy of the laser points. These processing bins were ultimately aggregated into areas of 0.9375-minute quadrangles (1/64th of a standard USGS 7.5-minute quadrangle).

Once the laser point data are imported into bins in TerraScan, a manual calibration test is performed to assess the system offsets for pitch, roll, yaw and scale. Using a geometric relationship developed by Watershed Sciences, 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. Each bin is then inspected for pits and birds manually, and spurious points are removed. For a bin measuring 1 km2, an average of 20-40 points are found to be artificially low or high.

The 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, yaw and scale offsets). Once these misalignments are corrected, GPS drift can then be resolved and removed. The resulting dataset is internally calibrated using both manual and automated routines. At this point in the workflow, remaining data have passed initial screening and are deemed accurate.

The TerraScan software suite is designed specifically for classifying near-ground laser points (Soinenen, 2004). The processing sequence begins by ‘removing’ all points that are not ‘near’ the earth based on evaluation of the multi-return layers. The resulting bare earth (ground) model is visually inspected and additional ground 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: bedrock outcrops, cliffs, deeply incised stream banks, and dense vegetation.

The NOAA Office for Coastal Management (OCM) received lidar point cloud files in laz format from the U.S. Forest Service. The files contained lidar elevation and intensity measurements. The data were in UTM 10N coordinates and NAVD88 (Geoid03) elevations, with all units in meters. The data were classified as: 1-Unclassified, 2-Ground.

OCM converted the data from orthometric (NAVD88) elevations to ellipsoid elevations using the Geoid 03 model and converted from UTM 10N NAD83 coordinates in meters, to geographic coordinates. Geokeys were also assigned. These conversions were done to ingest the data into the Digital Coast Data Access Viewer.