Laboratory Techniques and Procedures Using Lidar
ERDC VICKSBURG United States
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PURPOSE This Coastal and Hydraulics Engineering Technical Note CHETN reviews the process of establishing effective and accurate techniques for the application of lidar in the laboratory with a large model domain and a need to accurately resolve issues such as local pier scour and bathymetrytopography changes. The application is for both terrestrial and line-scanning lidar. INTRODUCTION Lidar scanning is a process that collects high-resolution geometric, bathymetric, and topographic data. Lidar uses light pulses to conduct remote sensing and to collect high resolution data typically referred to as a point cloud. Most scanners mount on a survey tripod or other fixed support structure and can rotate 360 referred to as a panoramic scan. The key component in the scanner is the polygon-shaped mirror that has flat reflective surfaces mirror facets arranged around a wheel perimeter to allow rotating or oscillating movement of the polygon mirror wheel Figure 1. This allows for the measurement laser beam to be deflected, thus scanning multiple locations at once RIEGL 2017. A brief review of lidar can be found in Jaboyedoff et al. 2010. When studying sediment transport with a moveable bed model, it is advantageous to have data with high resolution and accuracy to evaluate bathymetric changes from hydraulic processes. For scaled physical models, the importance of accuracy in laboratory data collection is magnified due to the effects of geometric scaling. Geometry, reflectance properties of focus area, and coverage angles of point clouds are critical factors to consider for measurement accuracies Fidera et al. 2004. For example, in regard to reflectance properties, the laser scanner generates noise when scanning transparent objects such as acrylic or glass. This results in generation of excess inaccurate points in that area of the point cloud.
- Optical Detection and Detectors
- Test Facilities, Equipment and Methods