"Bed topography" refers to the physical shape and features of the ground surface beneath a body of water, such as a river, lake, or ocean. It describes the hills, valleys, and other formations on the floor of the water body. Full definition
«Greenland glaciers» varied vulnerability to melting: More accurate maps of bed topography reveal physical processes controlling retreat.» (sciencedaily.com)
«Without bed topography you can not build a decent ice sheet model,» said CReSIS director Prasad Gogineni. (sciencedaily.com)