Age of Electronics (1923-1945)
The first great era of ocean exploration ended in the early 1920s, giving rise to new methods born of the fledgeling Electronic Age. In 1922, the USS Stewart was equipped with a Hayes echo sounder, designed by Dr. Harvey Hayes of the U.S. Navy. In 1923, the U.S. Coast and Geodetic Survey (C&GS, formerly the Coast Survey) Ship Guide was equipped with a Hayes echo sounder and proceeded to the North Pacific Ocean via the Panama Canal and the west coast of Mexico. Along the way, the Guide compared wireline and acoustic soundings in depths ranging from 100 to 4,617 fathoms. This work laid the basis for early work in determining accurate values for the velocity of sound in seawater. Over the next few years, virtually every U.S. Coast and Geodetic Survey ship was outfitted with the new echo-sounding technology.
The development of echo sounding continued in the ensuing years. By 1925 Submarine Signal Corporation was producing improved echo-sounding devices called fathometers. Herbert Grove Dorsey was a principal scientist during the development of these instruments and soon came to work for the Coast and Geodetic Survey as a physicist and inventor. Over the years, Dorsey developed a series of fathometers and echo sounders for C&GS ships. It was not until the late 1930s that sufficiently accurate and compact shallow-water echo sounders were developed to equip the Survey's small craft as well. By the eve of World War II, the majority of Coast and Geodetic Survey ships, as well as its smaller survey boats, were outfitted with echo sounders.
a time over a 40-year period beginning in 1925. Survey ships were assigned specific navigational tracklines to follow from the Straits of Juan de Fuca to their working grounds in western Alaska, the Aleutian Islands, and the Bering Sea. In addition to the policy of offset tracklines in the northeast Pacific Ocean, the C&GS also ran systematic surveys of five to 10 miles off many areas of the coast prior to World War II. This far-sighted policy led to the discovery of most of the major canyons that incise our continental shelf; many seamounts in the Gulf of Alaska and off the West Coast; the flat-topped seamounts, later termed guyots; delineation of the eastern extent of the Mendocino Escarpment, which was the first sea-floor feature to be recognized as a fracture zone; and further definition of the Aleutian Trench and Puerto Rico Trench, which had been discovered by earlier widely spaced wireline soundings.Radio Acoustic Ranging
Concurrent with the development of echo sounding, the C&GS developed radio acoustic ranging (RAR). Captain Nicholas Heck of the C&GS developed the concept for this system as a result of his World War I experiments in acoustic submarine detection, which he performed in cooperation with the Army Coast Artillery. Heck also cooperated with Dr. Carl Eckhardt of the National Bureau of Standards to build hydrophones and the electronics associated with the system.
RAR was the first navigation system that could be used around the clock and in all weather conditions. It involved setting hydrophones at known locations and throwing small explosives into the water from a survey vessel. The sound from the explosions would be heard on the ship and at the hydrophones. The hydrophones would radio back to the ship upon sensing the sound from the explosion. Surveyors on the ship then measured the time delay between sound reception of the explosion on the ship and reception of the radio signal from the fixed hydrophone. Then, they multiplied this figure by the velocity of sound in seawater to obtain a distance or range. Two or more hydrophones would provide intersecting ranges and fix the position of the ship.
Other inventions from this period with far-reaching implications were the early versions of continuously recording temperature versus depth instruments. Carl Gustav Rossby called his invention of such a device an "oceanograph," while Athelstan Spilhaus dubbed his invention the "bathythermograph." Although these early temperature-recording instruments have been superceded, the term "bathythermograph" still remains in common usage. Ultimately, these devices and their descendants, the CTDs or conductivity-temperature-depth recording devices and expendable bathythermographs (XBTs) by today's oceanographers, replaced the cumbersome reversing thermometers which, in practice, were used only to observe temperatures in the sea at preset discrete depths. Collectively, such instruments have done much to unravel the ocean's temperature structure and other aspects of ocean physics.