What is bathymetry?

Bathymetry is the study of underwater floors in oceans, rivers, or lakes.

Ocean mapping uses acoustics, satellites, light, and imaging, amongst other technologies to characterize the ocean floor. This information is critical for understanding and preparing for our ever-changing environment and increases our understanding of marine life. Video courtesy of NOAA Ocean Exploration, 2016 Hohonu Moana. Download larger version (mp4, 327.7 MB).

Bathymetry is the study of underwater floors in oceans, rivers, or lakes. It involves collecting information about the depth of the ocean. Bathymetry is the underwater equivalent to topography–the study of the surface structure on land. Just like dry land, the surface of the seafloor is not always flat. The seafloor can have coral reefs, mountainous ridges, deep canyons, and many other features that contribute to the variability of its surface. Bathymetry not only provides scientists with depth measurements, but also helps to create a picture of what the seafloor may look like.

Before modern technology, scientists would throw heavy lead weights attached to ropes over the side of boats and measure how much rope it took to reach the seafloor. However, due to water currents, this method often yielded inaccurate measurements and could lead to dangerous situations for ocean navigators. A surprise sandbar could endanger a ship’s crew or be detrimental for a ship’s cargo.

Today, scientists use single-beam and multibeam echosounders to make their bathymetric measurements. Echosounders send a pulse of sound from where they are mounted (generally on or near the hull or bottom of the vessel) to the seafloor. The sound wave travels to the ocean floor and bounces back. The time it takes for the pulse to return is used to determine the depth.

Scientists use collected bathymetry data to make bathymetric maps. Similar to topographic maps, bathymetric maps often use lines, or "contours," to show the shape and elevation of seafloor surface features. These maps help scientists in numerous ways, such as identifying geological faults and providing essential information for improving earthquake or tsunami prediction and response, modeling underwater habitats, developing models to predict coastal flooding risks, and increasing overall public awareness over ocean and coastal issues.


By Lia Kim, 2024 Explorer-in-Training
Published July 1, 2024

Relevant Expedition: Beyond the Blue: Papahānaumokuākea Mapping 1