Underway Bathymetry

Underway bathymetry is depth data logged opportunistically while a vessel transits between planned survey lines or sails a passage, rather than on dedicated survey lines. A hull-mounted single-beam or multibeam echosounder records soundings during the transit, adding coverage at no extra ship time. The data is lower-controlled than a planned survey: line spacing is uncontrolled, calibration patches may be old, and gaps are large, so it usually serves reconnaissance, GEBCO crowd-sourced bathymetry, and gap-filling rather than chart-grade survey. Crossover analysis at track intersections checks its consistency. It rarely meets a full IHO S-44 order on its own.