The gravity-based methods require the ship track data as well -- they're not fully independent methods. (i.e. not only are they calibrated to it, ship-track ba

The gravity-based methods require the ship track data as well -- they're not fully independent methods. (i.e. not only are they calibrated to it, ship-track bathymetry is actually half of the input data for gravity-derived bathymetry.) It's still really quite amazing how well it matches in an area that's pretty far from dense ship-track bathymetry data.