Long-Term Geometric Monitoring of the Bremen Cog: Monitoring Concept, First Results and Future Perspectives

Abstract. The Bremen Cog, a clinker-built vessel from 1380, is an outstanding cultural asset. The preservation of the conserved and reconstructed shipwreck is an important task. This article will give an overview on the geometric monitoring for the Bremen Cog implemented in 2020. Ten measurement epochs have been held since. The geometric monitoring focusses on two main aspects: recording rigid body displacement and determination of inner changes. A ground control network is installed and observed with a laser tracker network analysis. Due to the location of the museum, tidal changes lead to an instable geodetic datum over time. For the detection of inner changes of the cog, a large-volume photogrammetric metrology concept is realized. 364 photogrammetric targets on the cog represent its structure and potential critical parts. Additional targets allow for the determination of connection in changes between the support system and the cog. Interchangeable magnetic target adapters enable to use the ground control network for photogrammetric analyses. Different adjustment strategies are carried out and are still term of research. Initial results on vectorial displacements on inner changes are given, showing that the monitoring concept could be implemented successfully.