In March 2016, Quantum Spatial (QSI) was contracted by the United States Geological Survey (USGS), in collaboration with the Washington Department of Natural Resources (WADNR), to collect Light Detection and Ranging (LiDAR) data for the Western Washington 3DEP QL1 LiDAR project site in the state of Washington. The Western Washington 3DEP LiDAR project area covers approximately 3.5 million acres within portions of thirteen counties in the state of Washington; Whatcom, Skagit, Snohomish, Thurston, Lewis, Clark, Cowlitz, Wahkiakum, Skamania, and Grays Harbor. Data were collected to aid USGS in assessing the topographic and geophysical properties of the study area.

For the Western Washington 3DEP LiDAR project, the monument coordinates contributed no more than the listed positional error to the geolocation of the final ground survey points and LiDAR, with 95% confidence.

Upon completion of data acquisition, QSI processing staff initiated a suite of automated and manual techniques to process the data into the requested deliverables. Processing tasks included GPS control computations, smoothed best estimate trajectory (SBET) calculations, kinematic corrections, calculation of laser point position, sensor and data calibration for optimal relative and absolute accuracy, and LiDAR point classification (Table 9). Processing methodologies were tailored for the landscape.

The ocean surrounding the Western Washington 3DEP site and other water bodies within the project area were flattened to a consistent water level. Bodies of water that were flattened include lakes and other closed water bodies with a surface area greater than 2 acres, all streams and rivers that are nominally wider than 100 feet, and all tidal waters bordering the project. Islands within water bodies with area greater than 1 acre were not hydroflattened, with select smaller islands and features remaining as feasible. The hydroflattening process eliminates artifacts in the digital terrain model caused by both increased variability in ranges or dropouts in laser returns due to the low reflectivity of water.

Hydroflattening of closed water bodies was performed through a combination of automated and manual detection and adjustment techniques designed to identify water boundaries and water levels. Boundary polygons were developed using an algorithm which weights LiDAR-derived slopes, intensities, and return densities to detect the water’s edge. The water edges were then manually reviewed and edited as necessary.

Once polygons were developed the initial ground classified points falling within water polygons were reclassified as water points to omit them from the final ground model. Elevations were then obtained from the filtered LiDAR returns to create the final breaklines. Lakes were assigned a consistent elevation for an entire polygon while rivers were assigned consistent elevations on opposing banks and smoothed to ensure downstream flow through the entire river channel.

Water boundary breaklines were then incorporated into the hydro-flattened DEM by enforcing triangle edges (adjacent to the breakline) to the elevation values of the breakline. This implementation corrected interpolation along the hard edge. Water surfaces were obtained from a TIN of the 3-D water edge breaklines resulting in the final hydroflattened model.

In March 2016, Quantum Spatial (QSI) was contracted by the United States Geological Survey (USGS), in collaboration with the Washington Department of Natural Resources (WADNR), to collect Light Detection and Ranging (LiDAR) data for the Western Washington 3DEP QL1 LiDAR project site in the state of Washington. The Western Washington 3DEP LiDAR project area covers approximately 3.5 million acres within portions of thirteen counties in the state of Washington; Whatcom, Skagit, Snohomish, Thurston, Lewis, Clark, Cowlitz, Wahkiakum, Skamania, and Grays Harbor. Data were collected to aid USGS in assessing the topographic and geophysical properties of the study area.

For the Western Washington 3DEP LiDAR project, the monument coordinates contributed no more than the listed positional error to the geolocation of the final ground survey points and LiDAR, with 95% confidence.

Upon completion of data acquisition, QSI processing staff initiated a suite of automated and manual techniques to process the data into the requested deliverables. Processing tasks included GPS control computations, smoothed best estimate trajectory (SBET) calculations, kinematic corrections, calculation of laser point position, sensor and data calibration for optimal relative and absolute accuracy, and LiDAR point classification (Table 9). Processing methodologies were tailored for the landscape.

The ocean surrounding the Western Washington 3DEP site and other water bodies within the project area were flattened to a consistent water level. Bodies of water that were flattened include lakes and other closed water bodies with a surface area greater than 2 acres, all streams and rivers that are nominally wider than 100 feet, and all tidal waters bordering the project. Islands within water bodies with area greater than 1 acre were not hydroflattened, with select smaller islands and features remaining as feasible. The hydroflattening process eliminates artifacts in the digital terrain model caused by both increased variability in ranges or dropouts in laser returns due to the low reflectivity of water.

Hydroflattening of closed water bodies was performed through a combination of automated and manual detection and adjustment techniques designed to identify water boundaries and water levels. Boundary polygons were developed using an algorithm which weights LiDAR-derived slopes, intensities, and return densities to detect the water’s edge. The water edges were then manually reviewed and edited as necessary.

Once polygons were developed the initial ground classified points falling within water polygons were reclassified as water points to omit them from the final ground model. Elevations were then obtained from the filtered LiDAR returns to create the final breaklines. Lakes were assigned a consistent elevation for an entire polygon while rivers were assigned consistent elevations on opposing banks and smoothed to ensure downstream flow through the entire river channel.

Water boundary breaklines were then incorporated into the hydro-flattened DEM by enforcing triangle edges (adjacent to the breakline) to the elevation values of the breakline. This implementation corrected interpolation along the hard edge. Water surfaces were obtained from a TIN of the 3-D water edge breaklines resulting in the final hydroflattened model.