This paper reports the design and development of an underwater laser scanning system to measure the geometry of underwater objects. The application of structure light scanning method requires a calibrated CCD camera as the input device. Because the underwater environment is by far different from that in the air. Conventional calibration methods adopted in the air can not be applied for the underwater cases. In this paper we propose an algorithm which is analogous to the idea of longitudes/latitude in map projection to calibration the CCD. The calibration board pattern is fabricated by laying vertical and horizontal grid dots of 5cm span with an NC milling machine. To obtain the higher accuracy, we redesign the laser source holder to make the board and laser scan line coplane. We use a new laser that is focus adjustable. So we can capture clearer image of the edge on the target. Then, we calibrate the CCD camera with the calibration board. For testing our new system, two test pieces are used. One is sine waves ripples with varying amplitudes from 8mm to 3 mm. The other one is a rough surface with know spatial power spectrum. Scanning results show that: Scanning from rough 1 meter away, the absolute error for the sine wave ripples is less than 1mm along vertical direction. The power spectrum for the rough surface is accurate to the order of 3 to 5mm wave number. In order to survive in the harsh underwater environment, we design and make a rotational scanning system. The system was designed as an automatic image-capturing system, utilizing single board computer as control plane to work in conjunction with PLC(Programmable Logic Controller) for System power management. When using two 12V batteries as main power source, obtaining samples once per hour, capturing 360 images per operation, the system may run for approximately 39 hours.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0729104-172030 |
| Date | 29 July 2004 |
| Creators | Li, Jiu-min |
| Contributors | Chau-Chang Wang, Hsin-Hung Chen, Jen-hwa Guo, Chi-Cheng Cheng |
| 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-0729104-172030 |
| Rights | unrestricted, Copyright information available at source archive |
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