Multibeam Sonar
The difference between a basic sonar and a multibeam sonar is that a multibeam sonar is able to send beams that show a detailed map of the ocean floor and even includes silhouettes of the objects at the bottom of the ocean. This helps scientists have a view at whats at the bottom of the ocean but also map out paths to help guide them.
Ocean Pathfinder
People began by using leadlines. They tied a 10 pound lead weight onto a rope and lowered it until it was at the bottom of the ocean. They noted what they heard while something happened for records. People would risk their own lives in order to conduct soundings. Scientists conduct experiments to test theories of sound bend. Nowadays scientists use electronic waves that echo throughout the water.