noun
submarine topography; seafloor topography
Technical term used in oceanography and geology to describe the shape and features of the ocean floor.
海底地形の調査にはソナーが使われる。
Sonar is used to survey submarine topography.
地形 is general 'topography' or 'terrain'; 海底地形 specifically refers to the underwater seafloor.
Compound of 海底 (かいてい, 'seafloor') and 地形 (ちけい, 'topography').