碩士 / 國立臺灣大學 / 海洋研究所 / 100 / The study is to measure currents and sound speeds using ocean acoustic tomography (OAT). The thesis consists of a field experiment and numerical simulations. First, a reciprocal acoustic transmission experiment was conduced in Bachimen Narrows, which separates Hoping Island from Keelung during the spring tide period. Two acoustic tomography systems were situated on two sides of the water way, spaced with a distance of 500 m. Each station was equipped with a transceiver and GPS receiver. Reciprocal sound trans- mission experiments were successfully completed for 4 hours, using a carrier frequency of 10 kHz phase-modulated with the M sequence of 10th order. Range-averaged current and sound speeds, estimated from travel time data obtained reciprocally, show trends similar to the results of Horizontal Acoustic Doppler Current Profiler (HADCP) and the Conductivity-Temperature-Depth instrument (CTD) measurements. It is suggested that reciprocal sound transmission is applicable to current and sound speed measurements in the harbor sea.
Second, a numerical simulation was used to investigate the performance of OAT method for 2-D current field reconstruction. An artificial two-dimensional random streamfunction was generated from the Gaussian wavenumber power spectrum with dominating correlation length of 5 km in both x and y directions. From the synthetic streamfunction, the differential travel times were computed between all pairs of tomographic stations as the input data to the inversion. Tikhonov regularization method is applied to solve the inverse problem with the regularization parameter determined by the L-curve criterion. Different number of stations (8, 10 and 12), various array geometries (circular, zonal, and meridional distributions) are used to reconstruct the cur- rent field, with/without the station position errors included. It is suggested that, for the same number of stations, the circular array geometry gives the best inversion results. Using this synthetic current field, the result from 10 stations located circularly on the periphery of the field performs the best of all the other cases.
| Identifer | oai:union.ndltd.org:TW/100NTU05279026 |
| Date | January 2012 |
| Creators | Yen-Hsiang Chen, 陳彥翔 |
| Contributors | 黃千芬 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 89 |
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