What two pieces of information are needed to determine ocean depth through echo sounding?

To determine ocean depth through echo sounding, two key pieces of information are needed: the time it takes for a sound pulse to travel from the ship to the ocean floor and back, and the speed of sound in water. By measuring the time interval and knowing the speed of sound, the depth can be calculated using the formula: depth = (time × speed of sound) / 2. This accounts for the sound wave traveling to the seabed and returning to the surface.