Frequency (Hz)

Figure 9.5 Sampled envelope function (a) and energy spectra (b) for quantized Hanning transmit envelope used in an example from the REVMOD reverberation model. (Hodgkiss, 1984; IEEE J. Oceanic Eng., 10, 285-9; copyright by IEEE.)

component contributed only to spectral broadening of the transmit spectrum since the water column was assumed motionless on average. In this particular example, bottom backscattering was not a factor owing to the bottom-mounted transducer geometry.

For the purposes of discussion here, only a downwind transducer orientation is considered, although Hodgkiss (1984) also addressed upwind and crosswind orientations. This downwind case considers only the reverberation received at a range of 400 m. A quantized Hanning transmit envelope (Figure 9.5) and a Hanning receive envelope (Figure 9.6) are used in conjunction with the beam pattern shown previously in Figure 9.4. The transmit beam vector is horizontal and the receive beam vector is inclined towards the surface 25° off the horizontal. The transmit and receive envelope durations

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