Accuracy evaluation of multibeam echo sounder systems

To ensure the quality of multibeam bathymetric data, it is essential to carry out a rigorous accuracy assessment of the processed survey results. Although many domestic standards advocate using the root mean square error derived from discrepancies at primary cross-check points as a means of evaluation, this approach has shown significant sensitivity to water depth, often failing to objectively reflect the overall measurement accuracy. Consequently, its effectiveness in representing survey quality is limited. To address this issue and provide a more comprehensive reflection of multibeam survey accuracy, this study proposes a combined assessment method based on both internal and external consistency metrics. Using the Norbit400L multibeam echo sounder system as a case study, we evaluate the system's accuracy through comparative analyses of internally and externally consistent depth measurements. Field validation was conducted in the artificial island and tunnel section of the Hong Kong-Zhuhai-Macao Bridge. The proposed methodology offers a valuable reference for determining accuracy specifications of other multibeam systems.