Detection and empty volume measurement and calculation method of artificial reef groups in marine pastures

In recent years, the rapid development of social economy and a sharp increase in resource demand have spurred rapid growth in the construction of marine ranching. The deployment of artificial fishing reefs during marine ranch construction and their subsequent status monitoring are crucial. Monitoring encompasses not only the distribution range and condition of artificial fishing reefs and the scouring of the surrounding seabed but also the verification of the effective spatial volume of the deployed artificial fishing reefs to compliance with technical indicators during marine ranch construction. This paper exemplifies the detection and empty volume calculation of artificial reefs to ascertain their location and volume. Initially, a high-resolution Multibeam Echo sounder sonar system (integrated with high-precision attitude measurement system) and a high-precision Global Navigation Satellite System are employed to accurately capture the underwater location, shape, and seabed topography of artificial reefs. Subsequently, various volume calculation methods are analyzed based on the geospatial data obtained from precise measurements. An optimal method is then selected to calculate the volume of the artificial reefs and compared with the actual volume. The results indicate a high consistency between the method used in this study and the actual location of the artificial reef. For empty volume calculation, the error was 25.76% for a long-standing reef, while it was only 2.22% for a newly placed one. This study demonstrates that the method can accurately determine the location and morphology of artificial reefs and accurately calculate the empty volume for new artificial reefs. However, due to factors such as scouring and subsidence, discrepancies are observed in the calculations for long-standing artificial reefs. The findings also confirm that the integrated use of sonar and high-precision positioning equipment is effective for an objective and equitable evaluation of marine pastures construction.