11:00 AM - 1:00 PM
[SCG53-P03] Lake bottom images using ROV around the lake bottom seepage area of the Lake Biwa
Keywords:Lake Biwa, lake bottom seepage, ROV
There is a flat depression at the depth of 90-100 meters around the north-wenstern area of the Biwa lake off Takashima city. Many lake bottom seepage points on the depression area have been pointed out, and the disribution of these points are lined in a north-south direction. The contribution of ground water seepage from the lake bottom is estimated to be about 10 to 20 %, however their actual condition is not clear at the lake-bottom. To confirm the lake bottom seepage, we planed the visial observation, core sampling and direct sampling of bottom seepage using a small ROV.
In April 2021, the University of Shiga Prefecture began to operate the renewed research vessel “Hassaka II” equipped with a multi-beam type fish finder at the botteom of the vessel. Before the ROV dive, we first tried to detect the water coloumn acoustic anomaly with the lake bottom seepage using fish finder of “Hassaka II”, and them we applorced a detected point of acoustic anomaly. After anchring near the annomaly position, we started the ROV dive. As this multi-beam type fish finder can detect the horizontal position of the acoustic anomaly, we operated the ROV observating the display of fish finder. The lage bottom was siderly covered with soft sediment. Therefore, the vertical thrusters of ROV often rooled up the sedimet near the lake bottom, and making it difficult to peration the ROV. On the other hand, there were many white patchs on the lake bottom floor nearby the acoustic anomaly area and some small crator0like structure were found with white patch. Aroud white patch area, many gammaridean amphipods were also observed. During the dive on August 30m 2021, we could find bublles assenting from some crater-like wthite patch areas.
For enhancement of the ROV ability, we attempted to implementa the USBL and DVL to detect the ROV position in water and lake floor. We confirmed the USBL and DVL function at the Decenber 3, 2021, although we could not fully verify their function due to the occurrence of the ROV trable. Due to the low sensitivity of the ROV’s built-in camera, we also installed a small standalone 4k camera that be attached to the ROV, and succeded the acquisition of clear images of the lake bottom at the same dive.
In April 2021, the University of Shiga Prefecture began to operate the renewed research vessel “Hassaka II” equipped with a multi-beam type fish finder at the botteom of the vessel. Before the ROV dive, we first tried to detect the water coloumn acoustic anomaly with the lake bottom seepage using fish finder of “Hassaka II”, and them we applorced a detected point of acoustic anomaly. After anchring near the annomaly position, we started the ROV dive. As this multi-beam type fish finder can detect the horizontal position of the acoustic anomaly, we operated the ROV observating the display of fish finder. The lage bottom was siderly covered with soft sediment. Therefore, the vertical thrusters of ROV often rooled up the sedimet near the lake bottom, and making it difficult to peration the ROV. On the other hand, there were many white patchs on the lake bottom floor nearby the acoustic anomaly area and some small crator0like structure were found with white patch. Aroud white patch area, many gammaridean amphipods were also observed. During the dive on August 30m 2021, we could find bublles assenting from some crater-like wthite patch areas.
For enhancement of the ROV ability, we attempted to implementa the USBL and DVL to detect the ROV position in water and lake floor. We confirmed the USBL and DVL function at the Decenber 3, 2021, although we could not fully verify their function due to the occurrence of the ROV trable. Due to the low sensitivity of the ROV’s built-in camera, we also installed a small standalone 4k camera that be attached to the ROV, and succeded the acquisition of clear images of the lake bottom at the same dive.