A depth sounder is a device used to measure the depth of water beneath a boat or ship. It works by sending sound waves from the surface down to the seabed. When these sound waves hit the bottom, they bounce back to the device, allowing it to calculate the depth based on the time it takes for the echo to return. Depth sounders are essential for navigation, helping to prevent groundings in shallow waters. They are commonly used in various marine applications, including fishing, boating, and marine research. Many modern depth sounders also display additional information, such as water temperature and bottom composition.