Bare earth digital elevation model (DEM) from 2011 LiDAR, Blue River Watershed

Acquisition.

The LiDAR data was collected on October 27, 28 and November 1, 2011.   The survey used a Leica ALS60ii laser system mounted in a Cessna Caravan 208B.  Near nadir scan angles were used to increase penetration of vegetation to ground surfaces.   Ground level GPS and aircraft IMU were collected during the flight.

Processing.

1. Flight lines and data were reviewed to ensure complete coverage of the study area and positional accuracy of the laser points.
2. Laser point return coordinates were computed using ALS Post Processor software, IPAS Pro GPS/INS software, and Waypoint GPS, based on independent data from the LiDAR system, IMU, and aircraft.
3. The raw LiDAR file was assembled into flight lines per return with each point having an associated x, y, and z coordinate.
4. Visual inspection of swath to swath laser point consistencies within the study area were used to perform manual refinements of system alignment.
5. Custom algorithms were designed to evaluate points between adjacent flight lines.  Automated system alignment was computed based upon randomly selected swath to swath accuracy measurements that consider elevation, slope, and intensities.  Specifically, refinement in the combination of system pitch, roll and yaw offset parameters optimize internal consistency.
6. Noise (e.g., pits and birds) was filtered using ALS postprocessing software,  based on known elevation ranges and included the removal of any cycle slips.
7. Using TerraScan and Microstation, ground classifications utilized custom settings appropriate to the study area.
8. The corrected and filtered return points were compared to the RTK ground survey points collected to verify the vertical and horizontal accuracies.
9.  Points were output as laser points, TINed and GRIDed surfaces.