Bathymetric data coverage and density from single-beam and multibeam echo sounding surveys using unmanned surface vehicles in shallow inland waters

Hydrographic surveys must comply with the IHO S-44 standard. For the most stringent orders (Exclusive, Special, and 1a), 100% seafloor coverage is required, posing challenges in shallow waters near the 1 m isobath. Recent advancements in unmanned surface vehicles (USVs) and the miniaturisation of hydroacoustic devices now enable high-precision surveys even in hard-to-access areas. This study presents an analysis of bathymetric data coverage and density obtained using singlebeam echosounders (SBES) and multibeam echosounders (MBES) systems mounted on unmanned surface vehicle (USVs). The SBES survey employed the AutoDron USV, while MBES data were collected with the HydroDron-1 USV. Coverage analysis used a 1×1 m grid. The results reveal significant differences between the two systems. The MBES achieved an average density of 7.71 pts∙m−2 (>94% of grid cells meeting the NOAA- recommended minimum of 5 pts∙m−2). Data of MBES also exhibited uniform coverage, supporting the development of high-resolution bathymetric models. By contrast, SBES produced an average density of only 0.69 pts∙m−2, with a sparse and irregular point distribution. Only 1.79% of grid cells met the recommended threshold, while 63.79% contained no data. Nevertheless, SBES proved effective in the very shallow nearshore zone inaccessible to MBES. To achieve full coverage in compliance with International Hydrographic Organization’s requirements, complementary methods such as bathymetric light detection and ranging, Global Navigation Satellite Systems-real time kinematic surveys, or structure from motion photogrammetry are essential. Integrating these technologies is required to produce reliable and complete seafloor models.