This work studies the application of laser structured light scanning to measure the small scale roughness of seabed. We use a CCD camera to capture the dislocation of laser light. The location of the laser light in pixel coordinates can be converted into world coordinates if the CCD camera is calibrated. We propose an algorithm which is analogous to the idea of longitudes/latitudes in map projection. The idea is to place a calibration board to be aligned with the laser scanning sheet. On the calibration board, grid points of 50mm are laid to represent the intersection of the longitudes and latitudes. The position of a point in pixel coordinates can be obtained by referring to its neighboring graticule. We designed three experiments to verify the accuracy of the system: The first experiment consists of measuring the distance between feature points on the calibration board, then check and correct the optic distortion effects of the lenses. The second experiment is to measure the slice of laser scanning image of a known object, and check the accuracy of our laser scanning system by measuring the object's height and width. In the third experiment, we measure an object which has a small height variety of its surface, to test the resolution of the system. The results indicate that the error is under 1%, only then that we proceed with the design, analysis, and measurement of artificial seabed. The artificial seabed model is made by using a 210mm * 210mm * 30mm acrylic board with sand ripples forms in the 150mm * 150mm square. The amplitude of the ripples is no higher/larger than ¡Ó 8mm, and no lower/smaller than ¡Ó 1.5mm. Contour map of the sand ripples would be plotted to analyze the results obtained from the measurements. The analysis is carried out by obtaining slice data from a reconstructed surface of the sand ripples, then compare it with the theoretical values. From the result we know that the error between sand dune ideal wave index and measured index is in the range of ¡Ó 2mm. To further test the system's tolerance with turbidity, we incorporate conditions which would alter environmental turbidity into the seabed experiments before running the experiments for analysis. The results show that the system is able to maintain a stable performance in an environment below 2.3 NTU (Nephelometric Turbidity Unit), and the error between ideal sand dune ideal wave index and measured index is still in the range of ¡Ó 2mm.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0712104-110223 |
| Date | 12 July 2004 |
| Creators | Cheng, Ming-Hsiang |
| Contributors | Hsin-Hung Chen, Chi-Cheng Cheng, Chau-Chang Wang |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0712104-110223 |
| Rights | unrestricted, Copyright information available at source archive |
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