2012 USFS Lidar DEM: Colville National Forest, WA

Airborne lidar collection period.

Custom download allowing user selection of area, projection, format, etc.

Bulk download of files.

Data report from the contractor. Represents the data as delivered to USFS. Modifications have occurred to the data, as noted in this metadata. The report also describes imagery products that NOAA did not receive.

Airborne acquisition was conducted between 10:00am and 2:00pm each day. The LiDAR survey utilized a Leica ALS50 sensor mounted in a Cessna Caravan. The system was set to acquire greater than 114,600 laser pulses per second and flown at 2000 meters above ground level (AGL), capturing a scan angle of ±14 degrees from nadir. These settings are developed to yield points with an average native pulse density of 2 points per square meter over terrestrial surfaces.

Aircraft position was measured twice per second (2 Hz) by an onboard differential GPS unit. Aircraft attitude is described as pitch, roll, and yaw (heading) and was measured 200 times per second (200 Hz) from an onboard inertial measurement unit (IMU).

The study area was surveyed with opposing flight line side-lap of at least 60% (greater than 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.

Resolve GPS kinematic corrections for aircraft position data using kinematic aircraft GPS (Collected at 2 Hz) and static ground GPS (1 Hz) data collected over geodetic controls using POSGNSS v. 5.3, Trimble Business Center v. 2.81, PosPacMMS v 5.4

Develop a smoothed best estimate of trajectory (SBET) file that blends post-processed aircraft position with attitude data. Sensor heading, position, and attitude are calculated throughout the survey using POSGNSS v. 5.3, PosPacMMS v5.4

Calculate laser point position by associating SBET information to each laser point return time, with offsets relative to scan angle, intensity, etc. included. This process creates the raw laser point cloud data for the entire survey in *.las (ASPRS v1.2) format, in which each point maintains the corresponding scan angle, return number (echo), intensity, and x, y, z information. These data are converted to orthometric elevation (NAVD88) by applying a Geoid 12 correction using OPTECH LiDAR Mapping Suite (LMS) v. 2.1

Import raw laser points into subset bins (less than 500 MB, to accommodate file size constraints in processing software). Filter for noise and perform manual relative accuracy calibration. Ground points are then classified for individual flight lines to be used for relative accuracy testing and calibration using TerraScan v.12, Custom Watershed Sciences software

Test relative accuracy using ground classified points per each flight line. Perform automated line-to-line calibrations 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 using TerraMatch v.12, TerraScan v.12, Custom Watershed Sciences software.

Assess Fundamental vertical accuracy via direct comparisons of ground classified points to ground RTK survey data with TerraScan v.12

The TerraScan software suite was used to generate digital elevation models from the point clouds.

The processing sequence began with removal of all points not near the earth based on geometricconstraints used to evaluate multi-return points. The resulting bare earth (ground) model was visually inspected and additional ground point modeling was performed in site-specific areas (over a 50-meter

radius) to improve ground detail. This was only done in areas with known ground modeling deficiencies, such as bedrock outcrops, cliffs, deeply incised stream banks, and dense vegetation. In some cases, ground point classification included known vegetation (i.e., understory, low/dense shrubs,

etc.) and these points were manually reclassified as non-grounds.

Digital Elevation Models were received by NOAA OCM from USFS. Data were converted from ESRI grid format to Cloud Optimized Geotiff.