** Progress in Earth and Planetary Science is the official journal of the Japan Geoscience Union, published in collaboration with its 50 society members.

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    Simple Evaluation of the Degradation State of Cultural Heritage Based on Multi-view Stereo

    Kuchitsu N, Morii M, Sakai S, Unten H

    Wareishi Rock Cliff Sculpture, Sea level change, Replica, Hiroshima Prefectural History Museum, Sagi Island

    Displacement map between the Wareishi Rock Cliff Sculpture (2016) and the replica (made I n 1986)

    The area where more than 3 mm of displacement was observed (red spots) concentrates between b: the supposed average sea level during high tide in 1986 and a: that in 2016

    In this study, degradation of cultural heritage is discussed based on the comparison between the present shape of the Wareishi Rock Cliff Sculpture and its replica made 30 years ago through simple three-dimensional measurement using a multi-view stereo. The Wareishi Rock Cliff Sculpture, an important cultural property of Hiroshima Prefecture, is located near a shoreline. Local people often highlight that the sculpture seems to have recently been suffering from rapid degradation because of the direct impact of tidal ebb and flow. The present three-dimensional shape of this sculpture was investigated through multi-view stereo technique to accurately estimate the current degradation state. The same investigation was performed on the replica of the sculpture made in 1986 using a mold and exhibited in the Hiroshima Prefectural History Museum. The difference between the present shape of the sculpture and that of the replica revealed through the above investigation can be regarded as degradation of the sculpture that has occurred over the previous 30 years. The result is as follows. The difference was detected mainly on the middle part of the sculpture, which is a belt-shaped portion parallel to the sea surface that is ~ 20 cm high. The total area where more than 3 mm of displacement was detected constitutes ~ 0.56% of the whole measured area. Accordingly, the degradation of the Wareishi Rock Cliff Sculpture does not seem to be recently accelerated but seems to be progressing at a regular pace since it was carved, especially in relation to the sea level rise. If the degradation extends up to the face of the sculpture in the future, some countermeasures may be required. The method used in this study will contribute to the conservation of cultural heritage through evaluating the degradation state of the heritage precisely and to the study of weathering by detecting long-term weathering.