Abstract. In the last few years, notable progress has been made in the field of non-invasive diagnostic for the monitoring of heritage assets. In particular, multispectral imagery (more specifically thermal images will be addressed in this manuscript) allows investigations in the non-visible range of the electro-magnetic spectrum to be effectively carried out. Many researchers are currently exploring the possibilities related to the use of this kind of images in photogrammetric SfM-based processes to produce 2D and 3D value-added metric products, characterised by high level of detail and spatial resolution, including the information connected to the non-visible data. A data fusion-based strategy enables co-registering visible and thermal images in order to exploit the higher spatial resolution of the traditional true colour images. However, there are still many shortcomings to be addressed to properly and efficiently orient TIR (Thermal Infrared) images, connected (among other factors) to their low spatial resolution, or to the low contrast between adjacent materials characterised by similar emissivity. This paper proposes two different workflows to process thermal images using SfM algorithms, applied to three different case studies, each characterised by different characteristics and features (size, morphology, emissivity of the materials, etc.). The different pipelines are described and the obtained results are critically evaluated considering the metric accuracy, 3D geometric reconstruction and noise, completeness of the data and overall quality of the generated dense point cloud. Additionally, the effectiveness of the adopted strategies in connection with the peculiar features of the analysed case studies is also considered.

Abstract. Rapid mapping techniques based on UAV photogrammetry and portable systems are increasingly helping cultural heritage sites’ digitization, in case of large contexts or complex accessibility. At the same time, a wider range of more consolidated image- and range-based approaches could be useful, but challenging to be applied depending on materials, accessibility, or light conditions. However, the fundamental issue of integrating and optimizing the large amount of metric data of different origins in 3D accurate models remains open. An integrated system is needed to support the work of expert conservator and restorers, as well as archaeological investigation, on onsite work and, mainly, on remote activity. This paper aims to present the metric survey project carried out in the Fort component of the World Heritage property Qal'at al-Bahrain – the Ancient Harbour and Capital of Dilmun. The Bahrain Authority for Culture and Antiquities (BACA) started the initiative towards the conservation of the historic forts of the Kingdom of Bahrain. This requires a tailored approach to the uniqueness and outstanding significance of the sites. The digital products are baseline data and support the future conservation decisions. The validation of the integrated approach adopted for the survey of the Qal’at al-Bahrain will be presented and discussed in this paper. The validation aims for the integrated pipelines are targeted focusing on the aspects connected to the repeatability and the applicability of the methodological approach in the other sites with the same context and features, and this may also lead to further future reflections related to the sustainability of the survey.