Since only a navy recruited and maintained on a volunteer basis was allowed to Germany, from 1919, Lichte continued his work in the industry for civil purposes. In April 1919, he submitted to Physikalische Zeitschrifte the first scientific paper on underwater acoustics, theoretically describing the sound speed stratification of the ocean, forming ocean-wide sound ducts. He started the paper with his motivation for the research: “Resumed navigation from and to German sea ports has raised the importance of delineating mine-free corridors. Underwater sound signals are among the most important tools to this end. Consequently, learning more about sound propagation in water is of considerable interest.” Lichte’s 1919 paper was largely unnoted by researchers in the United States and in England until the 1970s. Te paper was doubtless the outgrowth of the capability of early twentieth-century German physics applied to the defence of the Kaiser’s U-boat fleet during WWI (Urich, 1977). Lichte worked with Alexander Behm (1880–1952), who developed a working ocean echosounder in Germany at the same time as Reginald Fessenden was doing so in North America, and with Heinrich Barkhausen (1881–1956), who is best known for the discovery of the Barkhausen effect, the abrupt increase of the value of the magnetic field during magnetisation of a ferromagnetic material. Lichte was also instrumental in the development of the first sound films. After 1945 he settled for a position as Lehrer für Physik und Mathematik at Lilienthal-Oberschule in Berlin.


Chaim Leib Pekeris (1908–1993) was born in Lithuania and emigrated to the USA in 1925. In 1934 he started working within geophysics at MIT’s geology department and in 1941 he moved to the Hudson Laboratories doing military research. Pekeris moved to Israel in 1948 where he was one of the designers of the Weizmann Automatic Computer (WEIZAC), the first computer in Israel, and one of the first large-scale electronic computers in the world. John von Neumann and Albert Einstein were both members of an advisory committee that was established in 1947 for the planned computer in Israel, although Einstein did not support the idea. In response to the potential use of such a computer Neumann responded, “Don’t worry about that, if nobody else uses the computer, Pekeris will use it full time!” We might therefore state that Chaim Pekeris was among the first geophysicists who realised the huge potential of computers. Based on the earlier work by Lamb (1903), Pekeris was the


Figure 3.56: Chaim Leib Pekeris, physicist and mathematician.


first to develop the normal mode theory for acoustic waves propagating within shallow waters. His paper from 1948 entitled Teory of propagation of explosive sound in shallow water is a classic, widely used in underwater acoustics. Pekeris did not include a solid water bottom layer, but assumed acoustic wave propagation only. Later, Press, Ewing and Tolstoy included the effect of a solid water bottom, by combining the theory derived by Lamb in 1904 with the Pekeris normal mode theory from 1948. In a 1996 oral history interview, J. Lamar (Joe) Worzel (1919– 2008), an American geophysicist known for his contributions to underwater acoustics, underwater photography, and gravity


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measurements at sea, remembered his and Maurice Ewing’s collaboration with Pekeris (Worzel, 1996): “Our part was the experimental part. Tis was work we did during World War II… What happened there was we did the explosion sounds in shallow water and we found that the water wave in the ocean was dispersive with the high frequencies traveling fastest and the low frequencies traveling slowest. So you got a wave pattern like that in the water wave – well, we got together some data like that and we sent it to Pekeris and said that this looks like an important thing and we had no theory for it. Do you know of any theory that you have? And he wrote back and said funny you should ask because I wrote a theory out for that kind of situation about a year ago only we couldn’t find any data to fit it and so we filed it and I’ve never had any data until you sent me this. Can you send me more? … And so we sent him more. I had the responsibility of getting the records together to send him more and he wrote this theoretical business which I still have difficulty understanding but Ewing understood it as soon as he saw the graphs. Te data, all these graphs about what’s going on he understood immediately.”


Ernst Hjalmar Waloddi Weibull (1887–1979), a professor at the Swedish Royal Institute of Technology, and Scientific Advisor to the Swedish armaments company A. B. Bofors, is today primarily known for the Weibull-distribution used to model random lifetimes. However, he published a scientific paper on the propagation of underwater explosive waves in 1925. He observed that the exploding charge emitted a series of distinct pulses, originated by oscillations in the spherical volume of gas into which the explosive had been converted. In the context of this book we acknowledge his development of a reflection seismic method for measuring the thickness of the upper sediment layers in great ocean depths. Based on an invitation from the Swedish physicist and


Figure 3.57a Waloddi Weibull.


oceanographer Hans Petterson, Weibull had been experimenting for some years in Swedish coastal waters attempting to use reflection seismic to measure the thickness of the sediment layers, when in the spring of 1946 he participated in a test expedition with the Swedish government research ship the Skagerak down to the western Mediterranean with equipment tests for the upcoming Albatross expedition. His seismic method was considered to be a quick survey method that required a minimum outlay of time and money for investigations in deep waters. A depth charge was made to explode by means of an ignitor released through hydrostatic pressure in depths varying from 500 to 6,500m under the water surface but well above the sea bottom (Weibull, 1954). Te arrival at the surface of the sound waves set up by the explosion was registered by hydrophones hung out over the sides of the ship. Te hydrophones converted sound (pressure) waves into electrical impulses, which were transmitted by cable to an oscillograph in the onboard laboratory. On the resulting oscillograms it was possible to recognise signals set up by the direct sound waves of the explosion, followed by repeated echoes from the water


Weizmann Institute of Science


Sam C. Saunders


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