Underwater Investigation for Lake Ashinoko, Kanagawa, Japan by Using a Low-cost Side-scan Sonar Imaging

The authors investigated two water areas in Lake Ashinoko, Kanagawa, Japan by using a modern leisure-use side-scan sonar and its high-resolution sonar imaging feature. One is located in the northern area of the lake with an area of 500 m × 550 m, and the other is in the south covering an area of 500 m × 450 m. The previously studies reported that the presence of submerged woods carried by mass movements. The detailed bathymetric maps, the acoustic reflection distribution maps acquired by side-scan sonar, and 455 kHz high-resolution sonar images indicate the details of mass movement topography, surficial geology, and the shapes of submerged woods. The shapes of mass movement of two areas are different, one has a large separated block far off the coast, and the other has a feature of debris avalanches. This paper shows that the proposed low-cost underwater investigation method is effective for shallow water areas