How did scientists first map the ocean floor depth?

Answer 1

Hydrographic surveyors (as people who map the ocean floor are called) typically utilize sonar systems to measure water depths. The simplest form is a single beam echosounder mounted on the underside of a boat floating on the surface. Like a flashlight that illuminates a small area in the direction it is pointed, a single beam sonar is pointed down and ensonifies a small area on the seafloor beneath it. The echosounder emits a pulse of acoustic energy into the water. This energy will travel down through the water; when it hits the seafloor (or anything else in the water column) some of the energy will be reflected back towards the echosounder. The speed of sound in water varies based on temperature, salinity and pressure, but is usually in the neighborhood of 1500 meters per second. By measuring the amount of time it takes for the acoustic energy to make its round-trip journey, and multiplying it by the speed of sound in water, we are able to calculate the depth.

Answer 2

They pay the divers to go to the end of the ocean and measure the ocean floor depth

before divers dive they take a long endless string keep it up the surface then take it al the way down and cut to where it ends so that when they are finished they measure

Answer 3

Hess started it during WWII and continued afterward.