An instantaneous-profile laser scanner to measure soil surface microtopography
Résumé
Soil surface roughness affects overland flow and soil erosion processes, yet studies on roughness effects are hampered by the difficulty of acquiring microtopographic data. The purpose of this study is to develop an instantaneous surface-profile laser scanner that has significantly higher data acquisition rate and smaller overall size than previous laser scanners. This laser scanner consists of two diode lasers and a digital camera mounted on a single rail. The lasers project a bright line on the surface and the shape of this line, digitized by the camera from an oblique angle, changes depending on the surface microtopography. From the geometry of the laser-camera assembly, the line image is converted to surface heights using a calibration procedure based on a triangulation principle. A computer drives the translation of the laser-camera assembly along the rail, processes the images from the camera, and records the surface profile data during the scan. This ensures the reconstruction of the surface morphology by juxtaposing successive profiles. The current system can measure the microtopography of a 50 cm by 4 m surface with a positional and elevational accuracy of 0.5 mm. The scanner can digitize six surface profiles per second. This translates to a time of 7.4 min to scan a 4-m long section with profiles taken every 1.5 mm apart. The instantaneous-profile laser scanner is significantly faster than previous scanner technologies and allows new research opportunities in quantifying surface boundary processes, such as soil erosion.