Underwater Mapping in Shallow Coastal Waters Using MBES and Photogrammetry: Applications in Archaeology and Marine Habitat Monitoring

Abstract. This study explores the combined use of Multibeam Echosounder (MBES) and Structure-from-Motion (SfM) photogrammetry for high-resolution underwater mapping in shallow coastal environments. Focusing on Slovenian waters, the methodology was tested in two case studies: the Posidonia oceanica seagrass meadows near Koper, and the submerged archaeological site of Fizine. By integrating MBES and optical photogrammetry, the approach combined the spatial precision of sonar data with the detailed visual reconstruction capabilities of photogrammetry. In the case of Posidonia oceanica mapping, this integration enabled the detection of broader meadow structures through MBES, while photogrammetry—both underwater and aerial—allowed for the accurate delineation of meadow boundaries, especially in shallow or visually complex areas. The complementary strengths of the two methods improved the reliability of habitat classification across varying depths and environmental conditions. At the archaeological site of Fizine, MBES provided high-resolution bathymetry and structural layout of the submerged features, while underwater photogrammetry enhanced the spatial detail, capturing fine architectural elements such as stone alignments and basin walls that were not visible in acoustic data alone. Together, the methods produced comprehensive, georeferenced models well-suited for both habitat monitoring and cultural heritage documentation.