Enhancing Geomatics Techniques for Cultural Heritage through Multiwavelength Recording and Metric Data Fusion

The preservation and conservation of cultural heritage assets are elaborate tasks that abound with challenges. Geometrical complexity, multiplicity and degradation of materials, varying historical construction techniques, and a plethora of other intrinsic and extrinsic factors—including environmental pressures and past anthropogenic interventions—induce problems for protecting the historic built environment, archaeological remains, and antiquities. Therefore, extensive knowledge of these parameters is required to ensure the effectiveness of any implemented intervention. Thus, the comprehensive documentation and condition inspection become necessary to holistically address the state of preservation in order to understand the prevailing problems that place cultural heritage assets at risk. Furthermore, monitoring the state of preservation through time is fundamental for effectively interpreting the occurring degradation phenomena and a powerful tool for the decision-making process regarding material heritage protection. Systematic nondestructive acquisition and integrated processing of multisource scientific data play an essential role in surveying the state of preservation of cultural heritage assets. The need for multidisciplinary inspection methodologies has been frequently stressed in literature, mainly in application cases of monumental heritage and objects of outstanding value presenting extensive degradation. Likewise, the non-destructiveness of monitoring methods has often been highlighted as an important factor for safeguarding the condition of significantly deteriorated or already at-risk assets. Hence, active and passive close-range nondestructive sensing techniques and appropriate signal processing methods are regularly used as nondestructive sources of multi-disciplinary data useful for inspection and monitoring applications. Individual close-range sensing methods, including techniques for reality-based geometric recording of cultural heritage, are often considered separate practices. However, their integration has the potential to improve the documentation of the state of preservation, and to support diagnostics, as many evaluation methods can act complementarily. It should also be highlighted that imparting spatial properties to nondestructive evaluation methods allows for the better interpretation and visualization of the state of preservation, while facilitating the spatial fusion of multi-sensor data. At the same time, monitoring benefits from geometric recording methods in the sense of acquiring spatial data and utilizing valuable sensing metadata derived from the employed measurement instrumentation. Recognizing the contribution of implementing multi-sensor approaches for non-destructive documentation of cultural heritage structures and objects as part of the protection practice, this dissertation presents novel applied geomatics methodologies for enhancing the surveying process of cultural heritage, focusing on the metric implementation of state-of-the-art non-destructive recording techniques and the fusion of acquired multiwavelength data. It seeks to validate integrated multi-band recording solutions, which can support the multidisciplinary documentation and condition inspection of critical heritage infrastructure and other objects of historical significance. Following this rationale, close-range sensing techniques are evaluated on their capacity to produce metric, survey-grade results for cultural heritage. The novelty of the conducted research stems from the innovative integration of reality-based digitization and multiwavelength acquisition through 3D scanning, thermography, multispectral imaging, ground-penetrating radar, and the utilization of data sources that are traditionally considered qualitative to obtain metric/quantitative results. Particular emphasis is given to creating reproducible and, as much as possible, practical workflows considering their implementability for heritage science. The dissertation aims to shed light on the problematics of the individual and integrated use of sensing techniques, highlighting metric and radiometric requirements of the data fusion approaches, as well as their usefulness to interpret the condition of heritage assets. The second chapter of this dissertation delivers a comprehensive overview of the contemporary proximal sensing techniques employed for reality capture and nondestructive evaluation of heritage assets—including their basic operating principles and application scenarios. The third chapter deals with the state of the art on data fusion methodologies encountered in recent literature, outlining the different levels of integration and the challenges faced. The fourth chapter describes a methodology for recording and integrating multispectral terrestrial data and utilizing them in combination with image processing techniques to map the deterioration of heritage assets. Although the presented workflow is mainly evaluated for two-dimensional mapping, an extension to three-dimensional objects is also briefly discussed. The fifth chapter addresses a methodology for full three-dimensional integration of spectral imaging, metric surveying, image-based modeling, scanning, and ground-penetrating radar. The latter methodology is adapted and validated for both historical objects and structures, considering the uniqueness of each case study and the limitations faced. The last chapter of the dissertation discusses the results of the diverse case studies and experimentation scenarios and describes perspectives and outlooks.