By now the subject cultural heritage is high on the political agenda of the EC: In the next research framework program Horizon Europe (2021-2027) it is closely associated with the prominent subjects safety and climate change. Cultural heritage is in jeopardy – climate change, extreme weather events and man-made tragedies like the Notre Dame Cathedral fire in Paris that occurred a few months ago, and above all the booming mass tourism are severely threatening the cultural heritage. To overcome these challenges, research and technological development are required: sustainable preservation materials, new analysis methods, socioeconomic studies, and above all new technologies of digitalization and artificial intelligence.

In Germany and Europe, the Fraunhofer-Gesellschaft has a significant role that entails innovative technological research for the sake of contributing to the preservation of cultural heritage and sustainable development. The research alliance "Kulturerbe" (FALKE), which comprises institutes of the Fraunhofer-Gesellschaft, the Leibniz research museums, the Prussian Cultural Heritage Foundation, and the State Art Collections Dresden, has taken on the mission to provide and redevelop innovations and technologies for the preservation of our cultural heritage since its foundation in 2008. This challenge does not only concern the engineering sciences but also art history and perception and the disciplines restoration and preservation.

As part of the project "Kulturerbe I", which was run from 2015 to 2019 by the research alliance FALKE, methods to digitalize art objects and detect their possible damages have been developed. The object was to mobilize existing methods so that they can be applied in the showrooms and museums immediately. They include photogrammetry, structured light, terahertz technology, confocal microscopy, and ultrasound tomography. It is interesting to note in this context that microscopy is applied on antique sculptures to show paint residues, as the majority of antique sculptures was in color – a fact you can observe in the current exhibition "Gods in Color" at Liebieghaus Frankfurt.

In March 2020, the "Kulturerbe II" project will start as a follow-up. As part of one of the subprojects, the digitalization and analysis methods are planned to be transferred from the museum halls into urban and rural environments. Our city centers and the surrounding areas are filled with cultural heritage, which should be preserved and taken care of under the previously mentioned conditions: Documenting the current states and the multimodal continuous monitoring of cultural objects are significant proceedings followed in practice. Thanks to complete three-dimensional scans of the Notre Dame Cathedral in Paris, the historic heritage has been documented and virtually preserved, independent of the issue how it will eventually be restored. By applying suitable methods of representation, it is possible to experience the cathedral virtually and interactively. The Fraunhofer-Gesellschaft will continue to work within the project "Kulturerbe II" by developing methods within the subject areas ultrasound, photogrammetry, structured light, terahertz technology and confocal microscopy further to apply them in practice. Application includes drone technology so that complex and costly scaffolding of building sections can be replaced for digitalization and damage analysis.

One of the remits of the Fraunhofer Institute for Biomedical Engineering IBMT is to apply ultrasound technologies to detect damages at building sections made of stone. A focus lies in incorporating local partners that have a connection to the regional cultural heritage in project-related works. The Institute for Stone Conservation IFS Mainz and the Monument Office of the Saarland could be attracted as partners for the works in urban environments. The IFS Mainz is responsible for the Saarland region and does not only act when mining damages occur at historic buildings. The IFS rather keeps the natural stone register and lists and examines all natural stones used at historic buildings located in its area of responsibility. One aim of the project is to characterize the collection acoustically by applying ultrasound and to show changes that happened due to climate changes by drawing comparisons with measurements taken at the buildings themselves.

To address the same research question, measurements are also taken at historic buildings and fragments of antique buildings and art objects made of sandstone in cooperation with the Monument Office of the Saarland. Besides the ultrasound technology, terahertz technology is used by the Fraunhofer ITWM Kaiserslautern. As opposed to ultrasound technologies, terahertz radiation allows for a contactless spectroscopy. Both methods deliver complementary information about the state and the inner structure of the objects. The two technologies are complemented by 3D surface scanning with photogrammetry and structured light so that a "digital twin" of the object documenting the current state is created. The "twin" can then be used for future investigations.

The project is internally funded as a Fraunhofer Executive Board project upon the President’s recommendation and will last three years.

Technology Transfer – An Ultrasound System for a Rapid Damage and Material Analysis

The Fraunhofer IBMT particularly profits from technology transfer from biomedical to technical ultrasound: Electronic assemblies with one or more channels as the Digital Phased Array System (DiPhAS), which has been developed in the Main Department Ultrasound, can be trained with optimized output stages for higher power ranges. Imaging and tomography techniques that are established in medical diagnostics are further developed by adding new approaches of signal processing for the detection of cracks and flaws to inspect sculptures and to detect damages inside them (cracks, corrosion at reinforcements, etc.). The ultrasonic transducers that are required are adapted according to the material properties of the objects being examined, e. g. marble or sandstone, and used for the techniques developed for the three-dimensional ultrasound for automated and quick position feedback of the sensors, because ultrasound tomography, which is traditionally performed manually, can take several days depending on the sculpture. This is due to the variable surface geometry, the potential transducers’ positions and the complex data analysis. Developing a rapid automatable measuring procedure that follows monument protection guidelines would allow to measure larger arsenals of sculptures for the first time and to digitally provide the results for the public and the scientists.