2 3 4 6 8 10 20 30 50 Range, /-(km)

Figure 3.23 As in Figure 3.22, except at a frequency of 8 kHz (adapted from Condron et al, 1955 by Apel, 1987).

than this are strongly attenuated. Conversely, wavelengths much shorter (or frequencies much higher) suffer losses due to absorption and leakage. Thus, for a mixed layer of a given thickness, it follows that there is an optimum frequency for propagation at which the loss of sound is a minimum (Figure 3.25).

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