How does hydrography map lakes, inland seas, and oceans?

In the context of hydrologic sciences, hydrography is the science of compiling and producing charts of water-covered areas, focusing on determining water depths and the horizontal coordinates of points on the surface of a body of water.1

To map lakes, inland seas, and oceans, hydrographers perform two primary operations: position fixing and depth measurement.1

• Position Fixing: Modern techniques utilize radar, satellite tracks, and inertial guidance systems to continuously determine a vessel's location relative to fixed shore stations or satellite data.2
• Depth Measurement: Historically, this was done using a weighted sounding line. Today, the standard method is echo sounding, which measures the time interval for a sound pulse to travel from a vessel to the bottom and back. Because the speed of sound varies with water temperature, density, and salinity, these factors are accounted for to ensure accuracy.23

For detailed studies, researchers may also use sonar, underwater cameras, and laser devices from aircraft. The resulting data is used to create bathymetric maps, which depict submerged topography through contour lines connecting points of equal depth.245