Bathymetry is the study and measurement of the depth and shape of the ocean floor. Just as topography maps the mountains and valleys on land, bathymetric maps show the hills, trenches, ridges, and plains beneath the sea.

Mapping the ocean floor means measuring its depth and shape (bathymetry) using instruments like sonar, satellites, and ships.

Bathymetry is important because it helps with navigation, understanding ocean currents, predicting tsunamis, studying marine habitats, and mapping natural resources. It also helps scientists learn more about how Earth’s crust moves and changes over time. 

Sonar, short for Sound Navigation and Ranging, is a technology that uses sound waves to detect and locate objects underwater. It works much like how bats use echolocation or how dolphins find food in murky water.

Here’s how it works: a sonar device sends out a sound pulse (often called a “ping”) into the water. When this sound wave hits an object—like the ocean floor, a shipwreck, or a school of fish—it bounces back to the sonar receiver. The sonar system measures the time it takes for the echo to return. Because sound travels through water at a known speed (about 1,500 meters per second), scientists can calculate how far away the object is.

A multibeam echo sounder is a special type of sonar used to create detailed maps of the ocean floor. It works by sending out many sound waves (beams) from a ship toward the seabed instead of just one. These beams spread out in a fan shape beneath the ship, covering a wide area of the ocean floor.

When the sound waves hit the bottom, they bounce back to the sensors on the ship. The system measures how long each echo takes to return and uses that information to calculate the depth at thousands of points. By combining all these measurements, scientists can build a 3D image of the seafloor.

Multibeam echo sounders are much more accurate and efficient than older single-beam systems because they map a broad swath of the ocean in one pass. They are used for nautical charting, underwater research, pipeline and cable surveys, and even to discover shipwrecks or underwater volcanoes. 

It might seem impossible for satellites flying hundreds of miles above Earth to map the ocean floor—but they actually can! While satellites can’t “see” through the water, they can measure the shape of the sea surface, which gives clues about what lies beneath.

Here’s how it works: large underwater features like mountains, ridges, and trenches affect Earth’s gravity slightly. A seamount (an underwater mountain) pulls a little more water toward it because of its extra mass, causing the sea surface above it to bulge upward by a few centimeters. A deep trench, on the other hand, has less mass and creates a small dip in the surface.

Satellites equipped with radar altimeters can detect these tiny changes in sea surface height with amazing precision. By analyzing this data, scientists can estimate the shape of the seafloor below.

While satellite mapping isn’t as detailed as sonar surveys, it’s incredibly useful for covering the entire globe, including deep and remote oceans where ships rarely go. These maps help scientists study plate tectonics, ocean circulation, and earthquake zones, giving us a big-picture view of Earth’s underwater landscape. 

The ocean floor is made up of several major features that help shape Earth’s underwater landscape. Scientists often divide it into continental margins, deep ocean basins, and mid-ocean ridges.