| Biography | |
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 Prof. Masaji Watanabe Okayama University, Japan |
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| Title: Mathematical modeling and computational analysis of underwater topography with global positioning and echo sounder data | |
| Abstract: Recent disastrous flood events include 2018 Japan floods (July 2018), Typhoon 19 (Hagibis, October 2019) and the following heavy rain events, and July 2020 heavy rain disaster. Those heavy rain disasters brought severe damages. Such disastrous events may increase in frequency and scale as the climate change progresses, and it is important to prepare reliable data concerning capacities of water areas such as rivers, reservoirs, and coastal areas. This study demonstrates techniques to construct an underwater topography. Field measurements are conducted in a reservoir called Kojima Lake in Okayama Prefecture, Japan. Seto Inland Sea lies between the main island and Shikoku Island of Japan. Kojima Bay is situated in the main island coast of Seto Inland Sea. A part of Kojima Lake was isolated from the rest by embankment, and became a reservoir called Kojima Lake. Kojima Lake is suitable for our measurement. In a field measurement, positioning with RTK-GPS in VRS (virtual reference station) mode and sounding with an echo sounder are employed. A GPS antenna is attached at an upper end of a pole which is fixed to a boat, and an oscillator of an echo sounder is attached at the lower end of the pole submerged underneath water surface. As the boat travels, outputs from the GPS unit and the echo sounder unit are recorded. Longitude and latitude components of ellipsoidal data output from the GPS unit are projected to a rectangular coordinate system, and joined with depth data output from the echo sounder unit so that curves on an underwater topography are generated. A map on a finite dimensional space of continuous functions over a triangular mesh is formulated so that a fixed point corresponds to a surface fitting the tracks. Our techniques are illustrated with data obtained in recent measurement. | |
| Biography: Research Activity: Masaji Watanabe works in research areas of applied mathematics, and he focuses on practical application of mathematical techniques such as mathematical modeling, inverse analysis, and numerical simulation. His research fields include analysis of underwater topography. He has been working on measurement and analysis for joint studies concerning the subject. This study aims at establishment of hardware and software system for construction and update of underwater topography. As the climate change progresses, heavy rain events may increase in scale and frequency. On the other hand, underwater topography is subject to change due to sedimentation and erosion. It is indispensable to prepare updated information concerning water areas such as rivers, lakes, and coastal water areas for prevention of disastrous flood events. This study demonstrates a practical application of mathematical techniques to a real-world problem, and it is expected to contribute to prevention of disaster due to heavy rain. | |
