Collection, processing, and accuracy of mobile terrestrial lidar survey data in the coastal environment

Abstract

The purpose of this Coastal and Hydraulics Engineering technical report is to present how elevation data is collected along the coast using terrestrial lidar scanners coupled with a global position system/inertial navigation system and assess the accuracy of the data. A brief overview of the technology utilized on the vehicle platform is presented, along with upcoming improvements. This is followed by a description of the data processing techniques utilized to create three-dimensional point clouds. Subsequent to that is a presentation of an accuracy assessment to provide an overall system performance summary and provide a few examples of data products and their uses. The accuracy assessment of the system resulted in a mean horizontal error of 0.075 meter (m), mean vertical error of 0.099 m, mean total error of 0.129 m, and an average repeatability of 0.05 m. The results of this report suggest that assigning a single accuracy value to a mobile lidar survey may misrepresent some of the spatially variable error throughout the survey, and further work should incorporate full error propagation to each point.

Evaluating Collection Parameters for Mobile Lidar Surveys in Vegetated Beach-Dune Settings

“…Additional errors throughout the dune region (> 3 m NAVD88) could potentially result from RTK measurement errors on steep terrain, fewer RTK and CLARIS points for comparison in this upper dune zone, and/or a range-related bias in the CLARIS system. However, comparison of the CLARIS MTL to fixed control points in previously reported efforts (Spore and Brodie 2017) at the FRF suggests that range-related biases are unlikely in this case. When omitting values greater than 6 m, mean Z differences are less than 4 cm for all 14 data collections and for 6 out of the 14 collections the mean Z difference was less than 2 cm (data not shown).…”

Investigation into laboratory bathymetric measurement techniques

“…The radar used to measure the wave characteristics can be stationary (McNinch et al 2012) or mounted to a vehicle (Brodie 2010). Mounting the radar to a mobile vehicle allows for rapid bathymetric measurements through inversion for large sections of coastline in storm conditions (Spore and Brodie 2017). Bathymetric surveys can be used to validate and calibrate the calculated X-band radar bathymetry (Brutsché et al 2017).…”

Coastal Lidar and Radar Imaging System (CLARIS) lidar data report : 2011 - 2017

“…This report details the range of dates and area covered by 2011-2017 surveys. More in-depth details regarding the overall development of the system have been described by Spore and Brodie (2017).…”

“…Riegl's proprietary RiPROCESS software is used to filter terrestrial point cloud points based on the following parameters: base grid size, number of levels used in process, tolerance factor (cutoff planes for data), percentile (number of points within a cell that are below representative cell point to define a cell's local surface), and maximum slope angle. More filtering specifics are outlined in section 5.1 of Spore and Brodie (2017). Following marking of "unclassified" non-ground points (e.g., vegetation, sand fencing), the point cloud is exported as a single .LAS file or multiple, tiled .LAS or .LAZ files.…”

“…As with any interpolation routine, some error is introduced into the final DEM, as the gridded cell size is typically larger than the point-spacing within the classified point cloud. Spatial error may be observed in sharp slope breaks and discontinuities such as at the foot of vertical beach and dune scarps, steep-faced (near vertical) foredunes, and dune crest position (e.g., see Figure 15 in Spore and Brodie [2017]).…”