Evolutions of Echo Soundings
On April 15, 1912, the most famous maritime disaster of all time occurred, killing over fifteen hundred people. The RMS Titanic sank after colliding with an underwater iceberg unseen and undetected by the crew onboard. In the disaster’s wake, safety was a priority. Many scientists began working on a way to detect unseen icebergs from the ship in time to avoid these and other dangers. One of the first to succeed was German physicist Dr. Alexander Behm. In 1913, Behm filed a patent for the first echo sounder. This new technology built upon previous discussion of sound waves and created the first useful apparatus for the measurement of distance underwater. Echo sounding relies upon sound waves propagated out into the ocean. The time between the propagation of the wave, and its reflection is a measurement of how far the ship is from whatever object reflected the sound wave. Behm improved his apparatus by including a sonometer to measure the strength of the reflected echo, and by using this measurement as an indicator of distance, rather than time alone (Behm, 1). At the same time as Alexander Behm was building the first echo sounder, Canadian inventor Dr. Reginald Fessenden was working on a similar project. Fessenden was deeply affected by the Titanic disaster as well, and came to the same conclusion as Behm. He invented the Fessenden Oscillator in 1911 and patented in in 1917. In addition to the detection of icebergs, Fessenden wished to use his device to enable communication between ships. The oscillator was the first to include an electrical component; Fessenden’s co-researcher Robert F. Blake described it as “an oscillating electric motor-generator which has a strong electromagnet surrounding a central core” and importantly contained a diaphragm that vibrated when a sound wave hit it (Blake). This electrical element is very useful, in that the electrical interlocking of sound production and reception allows for great precision of timing.
Both Behm’s and Fessenden’s apparatuses were not as useful for detecting icebergs as they had hoped, but both proved to reflect sound waves off the ocean floor (Dorsey radio talk). Thus began perhaps the most important application of echo sounding—exploration and mapping of the seafloor. Dr. Harvey Hayes of the United States Navy developed a sonic depth finder in the early 1920s that improved upon both Behm’s and Fessenden’s models. Hayes’ sonic depth finder relied on the time in between propagated and reflected sound waves as a measure of distance, but incorporated geometrical equations to narrow down the depth measurement with precision. His sonic depth finder was also able to take soundings very quickly and in succession, making it possible to create a profile of the seafloor. Hayes summed up the importance of his work in a quote from a geologist, who said about the sonic depth finder, “Now for the first time in, history the practicability of securing a map of the vast unknown area of the ocean floors is assured…” (Hayes, 75).
Though the Hayes model was a significant improvement in precision and timing of soundings, it was still found lacking in an absolutely necessary area of the ocean. In shallow water, the sonic depth finder could not take echo soundings. Into this void swept Dr. Herbert Grove Dorsey. Dorsey tackled the problem of the difficulty of measuring shallow water by taking it upon himself to find a method of amplifying the sound waves. This lead to the invention of the Fathometer, an electro-mechanical sounding device that integrated light as well as sound as a measurement of depths. Previously, no echo sounder had been able to measure much less than forty fathoms; Dorsey’s Fathometer, however, could measure as little as six fathoms due to the amplification of the sound waves. In a radio talk given in 1932, Dorsey described the method so:
“In front of the disc is a sheet of glass on which is painted a circular scale marked in fathoms form zero to 100. Every time the [illuminated] neon tube passes the zero point of the scale, an electric current passes through a sounder bolted to the bottom of the ship and a sound is produced as a short whistle blast… they are “heard” by a receiver of submarine sounds…and are amplified using thermionic tubes…increases the loudness of the echoes so that the electrical energy will cause the tiny neon tube to make a single brilliant instantaneous red flash of light… opposite some mark on the scale, six fathoms for example, if that happens to be the depth of water through which the ship is passing.” (Dorsey radio talk)
In developing a method by which shallow water could be measured, Dorsey opened up yet another section of the ocean that could be explored and mapped by scientists.
At this point, echo sounding as originally established by Behm and Fessenden was in its last stage of development. From the 1940s onward, through World War II and in the postwar era, echo sounding transformed from the simple propagation and reception of sound waves to a tool that encompassed many technologies. Physicists like Paul Langevin of France and Constantin Chilowsky of Russia worked on honing the sound waves to an ultrasonic beam that could be directed like a headlight in order to detect submarines and other underwater objects, and technologies like multi-beam echo sounding and sidescanning were introduced to the original echo sounder. From the choppy sounding profiles achieved by the first scientists who were not even looking for them, we can now produce “sonar derived ‘pictures’ of the seafloor comparable to terrestrial aerial photography” (“Sounding Pole to Sea Beam”). Echo sounding evolved from a desperate tool developed as a reaction to a tragedy to an essential technology found on every seafaring vessel in its new name—sonar.
Behm, Alexander. “Improvement in or relating to a Method of and Apparatus for Measuring Distances under Water by means of Reflected Sound Waves.” German Patent 17,109. 21 July 1913.
Blake, R. F., 1914. “Submarine Signaling: The Protection of Shipping by a Wall of Sound and Other Uses of the Submarine Telegraph Oscillator.” Transactions of the American Institute of Electrical Engineers Vol. XXXIII, Part II: 1549-1561.
Dorsey, Herbert Grove, Principal Electrical Engineer, United States Coast and Geodetic Survey. 1932. “Echoes Gives Ocean Depths: A Radio Talk” presented Friday, September 16, 1932, under the auspices of Science Service over the Columbia Broadcasting System. Science Service, Columbia Broadcasting System, Washington, D.C. Unpublished Mimeograph. Held by NOAA Central Library.
Hayes, Harvey. “Measuring ocean depths by acoustical methods.” Presented at the Stated Meeting of the Institute held Wednesday, March 21, 1923. Reprinted by permission from The Franklin Institute, The Journal of The Franklin Institute. Vol. 197, No. 3, pp. 323-354 (March, 1924). Found via Washington Academy of Sciences.
“Sounding Pole to Sea Beam.” National Oceanic and Atmospheric Association. 8 June 2006. Web. 1 June 2013.