Prof.  Masaji  Watanabe
Okayama University,  Japan

Title: Computational study on underwater topography based on positional data and depth data

Abstract:

Recent disastrous flood events include 2018 Japan floods (July 2018), Typhoon 19 (Hagibis, October 2019) and the following heavy rain fall event, July 2020 heavy rain disaster, and heavy rain fall events from July 1st, 2021. Those heavy rain fall events brought about severe damage including human damage and building damage. Such disastrous heavy rain fall events may occur more frequently as the climate change progresses, and it is necessary to update information regarding water areas such as rivers, reservoirs, and coastal waters. This study demonstrates computational techniques to analyze underwater topography.
 Longitude and latitude components of ellipsoidal data recorded by a GPS unit are projected to a rectangular coordinate system, and results are combined with vertical components including depth data recorded by an echo sounder unit. The data processing leads to tracks on a floor, and to a mapping on a finite dimensional space of continuous functions over a triangular mesh. A fixed point of the mapping gives rise to an underwater floor that fits the tracks. This study illustrates our computational techniques with data obtained in measurement conducted in a reservoir called Kojima Lake located in Okayama Prefecture, Japan.

Key words: Underwater topography, RTK-GPS, Echo sounder, triangular mesh, piecewise linear continuous function

Biography: