| Summary: | 碩士 === 國立海洋大學 === 應用地球物理研究所 === 91 === Abstract
The Penghu Channel is the deepest sea floor terrain in the Taiwan Strait. Because of it’s sea floor topography, particularly due to the blockage of a shallow geological feature, the Yun-chang Rise, the bottom current is very stong. In May 2002, one of the China Airline flight, CI611, unfortunately, crashed to the north area of Penghu Channel. Marine research workers including us joined the rescue team to search for remains of CI611. During the search, we have collected a great deal of sonar data by Side-Scan, CHRIP, EK500 and 37.5 kHz sonar systems.
From these data, we have interpreted the different morphological sand dunes: a great quantify of crescent-type and wave-type, and a small amount of ribbon-type. The shapes of sand dune is a good indication for the speed and direction of bottom current. Measurement of these sand dunes from the image data, we have found that the most directions of bottom current is northwest. This direction is the same as the former studys that measured by the Shipboard Acoustic Doppler Current Profiler (Sb-ADCP). More detailed data of the bottom current in the Penghu Channel can be estimated by the side scan sonar data.
This study combine a methods of physical and geological oceanogrdphies is a new method to understand the bottom current as well as the sediment transportation and deposition in the Penghu Channel. It is aimded to compare the results of bottom current studies between sonar data and the Sb-ADCP data.
Both the crescent-type and waves-type sand dune are found in Penghu Channel. The crescent dunes are located in the middle of channel; the waves dunes are in both side of the channel. The angle of crescent dunes are concentrated in the direction of northwest (0°~N20°W), and the wave dunes are spread in (0°~N120°W). The result suggest that the Panghu Channel content different speed and directions of bottom current. The estimated speed are in the other of 1.5~2.0 kts, however, joining together with the tidal current, the speed can be up to 4 kts.
The Northwest and Southeast area of Penghu Channel are out of search area for the CI611 flight and we do not have the data to describe the directions and velocity of water currents. Though we may infer that these bottom currents may belong to a distributary current of Kuroshio and South China Sea current, flow through the Panghu Channel all the year round. It pass the west side of Yun-Chang Rise then continue to the north. It may explain why the remains of CI611 were found in the west side of Yun-Chang Rise and the coast area of Mainland China.
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