Which scientific device is best suited for mapping the ocean floor?

Sonar is the most suitable device for mapping the ocean floor because it utilizes sound waves to detect and analyze underwater objects and features. By emitting sound pulses and measuring the time it takes for the echoes to return, sonar can effectively create detailed maps of the ocean floor's topography. This technology is particularly valuable in deep-sea exploration, where visibility is limited, and traditional methods like visual mapping are ineffective.

The other devices listed serve different purposes. Radar, for example, is primarily used for detecting objects in the atmosphere or on land and does not perform well underwater due to the absorption and scattering of radio waves by water. A seismograph is designed to measure the motion of the ground during earthquakes and does not provide data about underwater topography. GPS is a satellite-based navigation system that determines location on Earth's surface but does not have the capability to map underwater landscapes. Thus, sonar stands out as the optimal choice for underwater mapping tasks.