The bottom of the sea is a difficult place to visit because it is too deep and dark for us human beings. As a result, scientists need to go on a ship and use sound to get an idea of the shape and structure of the seafloor:

Bathymetry: Echo sounders are instruments placed on research ships that send sound towards the seafloor and measure the time it takes for the echo to come back. By knowing the time, scientists are able to calculate how deep the seafloor is and to generate a map of the seafloor.

Side scan sonar imagery: The side scan sonar instrument shares the same principle as the echo sounder, but the sound is emitted and received from the sides of the instrument. In this way, marine geologists are able to obtain an image of the shadows of the features on the seafloor, which is very similar to a black and white photograph. The side scan sonar is important because it provides information on both the shape and the composition of the seafloor.

Seismic reflection: Sometimes scientists are interested in what is found underneath the seafloor. It is very expensive to drill holes into the seabed, so seismic reflection systems are used to send sound waves into the seabed and get an image of the rocks and sediment making up the seafloor, very similar to an X-Ray image.

There are also many other techniques that marine geologists use to study the seafloor:

Sampling: Nowadays scientists are able to get samples of rock or sediment from very deep parts of the ocean, using grabs, cores and drillings. These samples are studied in a laboratory to get information about the composition and age of the seafloor.

Seafloor gravity and magnetics: The force of gravity and the magnetic field is not the same everywhere in the world. Scientists look for local changes in gravity and magnetic field as an indication of variations in the type of rock.

Remotely Operated Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs): Nowadays, unoccupied underwater robots operated by a person on board a research ship, or controlled by a computer programme, are used to collect information in very deep regions of the ocean.