The main difficulty in creating such a map is that water is too refractive, absorbs and reflects light. Already at a depth of a few tens to hundreds of meters, the bottom becomes invisible beneath the water column. There were attempts to use ultrasonic instruments to study the bottom surface, but their range of action was usually limited to the route of passage of a scientific vessel.
David Sandwell of the Scripps Institute of Oceanography (San Diego, California) and Walter Smith of the National Oceanic and Atmospheric Administration for most of the past 25 years conducted negotiations with defense officials and US satellite operators to gain access to measurements of the gravitational field of the sea and the surface Of the Earth.
The result of their joint work was a huge amount of information about mountain ranges and valleys based on the changing gravitational field of the planet. So the shades of red and orange correspond to places where the seabed is under the greatest pressure, that is, in the locations of seamounts, ridges and along the edges of tectonic plates. The shades of blue coincide with the deepest ocean depressions.