Validation of Unmanned Surface Vehicle-Based Multibeam Echosounder Bathymetric Surveys: Comparison with Manned Platforms in Harbor and Island Areas

The demand for hydrographic surveys is increasing amid growing needs for environmental monitoring, climate response, and maritime safety, while traditional manned vessel surveys face operational limits related to cost, safety, and accessibility.Recent advances in autonomous navigation, remote communication, and multisensor integration technologies have accelerated the adoption of unmanned surface vehicles (USVs) for marine surveying.However, establishing the reliability of USV-based bathymetric surveys requires rigorous accuracy verification against conventional manned-vessel measurements.This study quantitatively evaluates the performance of multibeam echosounder (MBES) surveys conducted by USV in both harbor environments and complex island terrains by comparing them with manned vessel data collected over the same areas.Accuracy assessment was performed using three complementary approaches.First, crossline quality control analysis based on the International Hydrographic Organization (IHO) S-44 total vertical uncertainty (TVU) standards.Second, shallow water area analysis using statistical indicators.Third, raster-based depth difference analysis using a digital terrain model (DTM).As a result, both manned vessel and USV surveys satisfied 99.6-100% of the special order, order 1a/1b, and order two standards across all survey areas and years.In the shallow water analysis, the root mean square error (RMSE) was 0.07 m in Yongho Harbor and an average of 0.16 m in Dokdo, indicating excellent agreement between the two platforms.The raster-based depth difference analysis also demonstrated high spatial consistency, with a mean absolute error (MAE) of 0.08 m and a standard deviation (STD) of 0.12 m in the harbor area, while depth deviations in the Dokdo region remained within the IHO allowable limits for corresponding depths.Although localized deviations were observed due to the absence of confirmation surveys and the limitations of global navigation satellite system (GNSS) based positioning, the overall results show that USV-based MBES bathymetry achieves accuracy comparable to manned surveys while offering superior accessibility, safety, and operational efficiency in shallow or hazardous environments.These findings suggest that USVs have strong potential to serve as an alternative or complementary platform to traditional manned vessel hydrographic surveys.