When was most of the technology for collecting sea-floor topographic and magnetic data developed?

Question

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Answer 1

During the 1950's and 1960's.  The impetus was the targeting of Intercontinental Ballistic Missiles (ICBMs).  

ICBMs are only guided during the first several minutes of their flight, while the engines are still  burning.  After the engines burn out, the ICBMs just coast to their targets without any guidance.  

Variations in the gravitational field of the earth perturb the flight of the warhead.  Thus, it is very important  to know in detail how the gravitational field varies over the path flown by the ICBM between its launch point and its target.  

The presence of mountains, valleys, and plains affect the earth's gravitational field.  On land, these features can be photographed and measured and their effects readily calculated.  Since ICBMs are _intercontinental_ (that's their point), much of their flight occurs over the oceans.  The topographic features of the oceans cannot be seen directly, so it was necessary to develop methods for mapping the topography of the sea floor.  This occurred during the 50's and 60's because that is when ICBMs were developed.

Answer 2

Early sonar systems were developed during World War I, by the British, French, and Americans to locate underwater targets, such as submarines and icebergs. The Second World War saw the refinement of sonar systems in terms of signal strength and coherency. The advances that have led to our modern day systems began in the 1960's.  Today advanced sidescan sonar uses backscattered acoustic energy received from the ocean bottom to image the sea floor.

The fluxgate (and later the proton) magnetometer was originally designed and developed during World War II. It was built for use from low-flying aircraft as a submarine detection device. In 1955 it was used to detect the pole reversals recorded in the seafloor that gave great legitimacy to the theory of plate tectonics.