The Age of Electronics I (1923-1945)

Echo Sounding (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, the 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.

These early echo sounders led to many discoveries as C&GS ships began systematic surveys of the continental shelves and slopes of the United States and in the waters of the northeast Pacific Ocean. Some of these surveys were quite long term; for instance, the survey of the Gulf of Alaska was conducted one trackline at 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 5 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; flat-topped seamounts, later termed guyots; delineation of the eastern extent of the Mendocino Escarpment, which was the first seafloor 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.

RAR led to advances in the understanding of sound in seawater and gave a first glimpse of the potential for transmitting sound throughout oceanic basins. By 1925, observations had been made over a distance of 206 miles. The technology also led to the development of telemetering oceanographic instruments, including radio sono-buoys and the Roberts Radio Current Meter, perhaps the first moored telemetering instrument to measure and transmit observations of physical parameters within the oceanic water column.

Temperature and Depth Instruments

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) used 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.

During the decade before World War II, the embryonic oceanographic and geophysical community often visited the offices of the Coast and Geodetic Survey. Dr. Francis P. Shephard, the "father of marine geology," began his seafloor studies while visiting from the University of Illinois. Dr. Maurice Ewing, the "father of marine geophysics," often visited from Lehigh University, and Dr. Harry Hess, the "father of plate tectonics," also visited during these years. They came with other great names in the fields of geophysics, marine geology, and oceanography to review C&GS records, consult with fellow experts, and study C&GS instrumentation and methods. Many of them sailed on C&GS ships, accompanied geodetic and geophysical field parties, and had C&GS personnel accompany them during their field experiments. These were the formative years for many future leaders in marine science and geophysics, and the Coast and Geodetic Survey played an important role in their early professional experience.

The War Years

The advent of World War II proved a boon to oceanography. New instruments were developed and others, such as the previously developed bathythermograph and modified versions of RAR radio sono-buoys, came into widespread use as tools in submarine warfare. Early magnetometers, scanning sonars for submarine detection, and acoustic sounding instruments all led to a greater understanding of the oceans and the seafloor. Seafloor photography became a serious geologic and oceanographic tool during this period when Maurice Ewing developed an early deep-sea camera.

Perhaps the most important innovation to come out of the war, however, was the evolution of electronic navigation systems as an outgrowth of radar development. These navigation systems were used for precision aerial bombing navigation, but by the end of the war, both the British and the U.S. Coast and Geodetic Survey were using them to conduct hydrographic surveys.