Offshore underwater artificial structures (e.g., sea transmit pipeline) are susceptible to instability due to long-term hydrodynamic impacts, biological attachment or blockage, which requires regular detection and precise inspection. Grounded in the concept of multi-source data fusion, this study proposes an acoustic-optical multimodal joint diagnostic methodology. By integrating three underwater monitoring technologies—multibeam bathymetry, dual-frequency imaging sonar, and optical imaging from remote operated vehicle (ROV)—an acoustic-optical-topographic comprehensive data evaluation framework is established, with spatiotemporal registration and dynamic quantitative analysis methods for multi-sensor. Field tests demonstrate that this approach enables accurate defect identification in certain complex marine conditions, significantly improves detection efficiency compared to conventional methods, and effectively mitigates reconstruction errors induced by scouring. The findings provide valuable insights for the intelligent operation and maintenance of marine engineering structures such as offshore wind turbine foundations and cross-sea tunnels.

To address the limitation of traditional cross-sectional scanning methods for submarine pipelines, which only capture localized cross-sectional information and hard to detect continuous axial deformation features, this paper proposes a data fusion method based on acoustic sub-bottom profiling that integrates both cross-sectional and longitudinal scanning. By deploying survey lines both perpendicular and parallel to the pipeline axis, and utilizing a parametric sub-bottom profiler combined with a high-precision positioning system, this method enables the simultaneous extraction and comprehensive analysis of multiple parameters, including pipeline inclination, cross-sectional ellipticity, longitudinal elevation deviation, joint misalignment, and external environmental anomalies. Field tests conducted on a water pipeline in the South China Sea successfully identified five types of typical anomalies, including pipeline tilt, depressions, obstacles, and upheavals. The results verify the effectiveness and engineering applicability of the proposed method for diagnosing submarine pipeline stability, providing a reliable technical approach for continuous deformation monitoring and safety maintenance of long-distance submarine pipelines.