碩士 / 國立中山大學 / 海下科技暨應用海洋物理研究所 / 101 / Plate motions over the past few million years have averaged 1 10 centimeters per year. To monitor such slight deformations in the crust by the GPS/Acoustic geodesy, the accuracy on the order of a few centimeters in positioning seafloor transponders is required. Temporal and spatial variability of sound speed in the water column, however, as well as the measurement error of sound speed, is a main limiting factor in the production of accurate acoustic ranging even though frequent conductivity-temperature-depth (CTD) casts are made. Therefore, in this study, various geometrical options for acoustic ranging are designed in the numerical simulation of GPS/Acoustic geodesy and the effects of various sound-speed measurement errors on the accuracy of transponder positioning are evaluated. The simulation results show that observing slant-range measurements symmetrically around the transponder can nullify sound-speed errors in the horizontal but not vertical positioning of a seafloor transponder. Sound-speed errors produce the vertical positioning error although the slant-range observations are well geometrically balanced. For reducing the effect of sound-speed variation on the precision of GPS/Acoustic seafloor geodesy, this study proposes two synthetic sound-speed profiles of the water column, one linear and the other bilinear, to approximate acoustic travel-time measurements. The approximating sound-speed profile is used in combination with the tomographic estimation in GPS/Acoustic geodesy to estimate the sound speed variation, such that the effect of sound speed variation on the accuracy of transponder positioning is reduced. The performance of the two synthetic models is evaluated for different types of CTD-derived sound-speed profiles and for the acoustic ranging observations collected from a field GPS/Acoustic survey. The evaluation results demonstrate that both the linear and bilinear models can effectively reduce the effect of sound-speed variation on the precision of GPS/Acoustic positioning.
| Identifer | oai:union.ndltd.org:TW/101NSYS5281007 |
| Date | January 2013 |
| Creators | Jing-zhong Ding, 丁靖鐘 |
| Contributors | Hsin-Hung Chen, 陳信宏 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 67 |
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