3D change detection for cultural heritage monitoring: Two case studies of underground sculptural reliefs

The preservation of underground cultural heritage is a challenging goal. Difficult acquisition conditions, the need for uniformity of temporal data and the speed at which surfaces change are some of the issues to consider. Also, quantifiable three-dimensional data are often unavailable when assessing changes on sculptural reliefs because traditional records are two-dimensional. In this paper, we present a workflow to easily detect and measure 3D superficial changes in sculptural reliefs using the deviation analysis technique. We compared multitemporal surveys, testing a quantitative, replicable, and verifiable procedure in two case studies: the reliefs of Pakal's Tomb at Palenque, Mexico, and those of the Osimo Caves in Italy. Both are located underground and show similar superficial alterations such as material disaggregation, efflorescence, salt crusts, and biological colonization. The reliefs showed visible and quantifiable changes on the deviation maps. The procedure to detect changes can be implemented with models generated by structured light scanning as well as photogrammetry.