4:30 PM - 4:45 PM
[HTT14-05] Deciphering underwater archaeological sites (Lake Hibara site, Fukushima Prefecture) by microtopographic analysis using a multi-beam echo sounder
Keywords:Mt. Bandai, Underwater archaeology, Multibeam echo sounder, Topographic map, slope distribution map, Lake Hibara
Traces of submerged settlements on seabeds and lake bottoms, resulting from tectonic subsidence or sudden natural disasters, are potentially present both domestically and internationally. However, accurately assessing the spatial information and land-use classification of entire submerged settlements is challenging due to the depth of the water and the thick sediment cover. One potential solution to this issue is the utilization of high-resolution acoustic survey equipment, although there are limited examples of its application. In this study, a microtopographic survey was conducted using a multibeam echo sounder in and around the submerged settlement of the histrical post town of Hibara village. This village was submerged in a dammed lake, Lake Hibara, which formed as a result of the 1888 eruption of Mount Bandai.
The multibeam echo sounder utilized in this study was a NORBIT Winghead i77h (1024 beams), operating at a frequency of 400 kHz. Data processing was conducted using QPS Qimera post-processing software to generate 0.25 m and 0.15 m mesh data. Subsequently, the mesh data were converted into color-shaded elevation maps, as well as slope and curvature maps, along with the CS (Curvature and Slope) topographical map featuring superimposed curvature and slope data. To make these maps, a commercially available software tool, Surfer by Golden Software, was employed.
An attempt was made to reconstruct the streetscape of the village by comparing the features of each map with old map created before the village was submerged. The old map describes the type of land (residential land or field) and provide details such as length, width, and area of each parcel.
The slope map reveals that areas where residential zones and streets were situated exhibit relatively flat slopes, while field areas are located on sloping terrain. The CS map also exhibits distinct lineaments or intermittent linear structures and points that likely represent land boundaries, with these lineaments extending parallel or perpendicular to main street. Comparing the inferred land parcels from the CS map with those depicted on the old map indicated that the width and area of the land on the CS map closely matched the survey results of the old map. This finding suggests the higher reliability of the survey results from the old maps.
Therefore, the values in the old map were utilized to estimate the locations where the land parcels were unclear on the CS map. This approach facilitated the reproduction of the overall characteristics of the entire village and allowed for estimation of the locations of main street, paths, and streams.
However, certain map information depicted in the old map, such as a river running north-south through the western part of the village, could not be confirmed in aspects of the microtopography of the CS map or the shaded map. Similarly, the road from the western part of the village through towards Aizu downtown could not be identified. The northwestern part of Lake Hibara in the western section of the village marks the confluence of two rivers, the Aizu River and the Okawairikawa River. Therefore, it is plausible that the topographical features of the rivers and roads were obscured due to burial by river sediments deposited by the two rivers following the formation of the lake.
This study has facilitated a microtopographic analysis utilizing a high-resolution narrow multibeam system to reconstruct the land allotments of Hibara village and provide an overview of the townscape. It was observed that location information could be accurately reproduced for certain areas. Discrepancies in interpretation between the old maps and the microtopography are anticipated to be resolved through underwater excavations.
Acknowledgements: The multi-beam echo sunder analysis was conducted in collaboration with S.E.A. Corporation (https://www.seanet.co.jp/). This research was supported by JSPS Grant-in-Aid JP22H00028.
The multibeam echo sounder utilized in this study was a NORBIT Winghead i77h (1024 beams), operating at a frequency of 400 kHz. Data processing was conducted using QPS Qimera post-processing software to generate 0.25 m and 0.15 m mesh data. Subsequently, the mesh data were converted into color-shaded elevation maps, as well as slope and curvature maps, along with the CS (Curvature and Slope) topographical map featuring superimposed curvature and slope data. To make these maps, a commercially available software tool, Surfer by Golden Software, was employed.
An attempt was made to reconstruct the streetscape of the village by comparing the features of each map with old map created before the village was submerged. The old map describes the type of land (residential land or field) and provide details such as length, width, and area of each parcel.
The slope map reveals that areas where residential zones and streets were situated exhibit relatively flat slopes, while field areas are located on sloping terrain. The CS map also exhibits distinct lineaments or intermittent linear structures and points that likely represent land boundaries, with these lineaments extending parallel or perpendicular to main street. Comparing the inferred land parcels from the CS map with those depicted on the old map indicated that the width and area of the land on the CS map closely matched the survey results of the old map. This finding suggests the higher reliability of the survey results from the old maps.
Therefore, the values in the old map were utilized to estimate the locations where the land parcels were unclear on the CS map. This approach facilitated the reproduction of the overall characteristics of the entire village and allowed for estimation of the locations of main street, paths, and streams.
However, certain map information depicted in the old map, such as a river running north-south through the western part of the village, could not be confirmed in aspects of the microtopography of the CS map or the shaded map. Similarly, the road from the western part of the village through towards Aizu downtown could not be identified. The northwestern part of Lake Hibara in the western section of the village marks the confluence of two rivers, the Aizu River and the Okawairikawa River. Therefore, it is plausible that the topographical features of the rivers and roads were obscured due to burial by river sediments deposited by the two rivers following the formation of the lake.
This study has facilitated a microtopographic analysis utilizing a high-resolution narrow multibeam system to reconstruct the land allotments of Hibara village and provide an overview of the townscape. It was observed that location information could be accurately reproduced for certain areas. Discrepancies in interpretation between the old maps and the microtopography are anticipated to be resolved through underwater excavations.
Acknowledgements: The multi-beam echo sunder analysis was conducted in collaboration with S.E.A. Corporation (https://www.seanet.co.jp/). This research was supported by JSPS Grant-in-Aid JP22H00028.