Abstract
Rock art paintings present high sensitivity to light, and an exhaustive evaluation of the potential color degradation effects is essential for further conservation and preservation actions on these rock art systems. Microfading spectrometry (MFS) is a technique that provides time series of stochastic observations that represent color fading over time at the measured points on the surface under study. In this work, a reliable and robust modeling framework for a short and greatly fluctuating observation dataset collected over the surfaces of rock art paintings located on the walls of Cova Remigia in Ares del Maestrat, Castellón, Spain, is presented. The model is based on a spatially correlated spline-based time series model that takes into account prior information in the form of model derivatives to guarantee monotonicity and long-term saturation for predictions of new color fading estimates at unobserved locations on the surface. The correlation among the (spatially located) time series is modeled by defining Gaussian process (GP) priors over the spline coefficients across time series. The goal is to obtain a complete spatio-temporal mapping of color fading estimates for the study area, which results in very important and useful information that will potentially serve to create better policies and guidelines for heritage preservation and sustainable rock art cultural tourism.
Highlights
Prehistoric rock art paintings are exposed to environmental elements that can accelerate their degradation, increasing the risk of losing such valuable cultural assets from past societies
X-ray fluorescence (XRF) spectrometry has been essential for enhancing the current understanding of these materials, as can be seen from various studies conducted on several rock art sites from Valencia, Spain [67,68,69]
Color is an important aspect of the documentation and conservation of historical assets such as prehistoric rock art paintings
Summary
Prehistoric rock art paintings (see, for example, Figure 1, left plot) are exposed to environmental elements that can accelerate their degradation, increasing the risk of losing such valuable cultural assets from past societies. The present research is focused on the paintings located in Cova Remigia open-air rock art shelter in Castellón (Spain), which is part of the Spanish. In order to construct a model useful for making predictions of new functional data as a function of new values of the variables in the input space, the process must be considered as an structured process with dependence among observations. A popular approach for correlated space-time functional data consists of three-way (spatial, 2D, and temporal, 1D) penalized spline models [17] with different basis constructions based on Kronecker products [18,19] or additive basis components [20]. Et al [21] proposed a mixture of a functional regression model for functional response and a penalized spline spatial regression. In general, these models have large numbers of parameters
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