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Part No. 96000001
6.2 Sonic MBES Transmit (Normal Operation Mode)
The projector is comprised of a precisely arranged set of composite ceramics. The projector, itself,
can transmit over a wide frequency range, which makes it unique amongst multibeam
echosounders. A pulse, at the chosen operating frequency, excites the ceramics which converts the
electrical energy to acoustic energy. The pulse originates from the Wet Controller board in the
Receive Module, which is then passed onto the Transmitters and out to the Projector. The
amplitude of the pulse is set by the transmit Power setting in Sonic Control 2000; the Pulse Length
setting in Sonic Control 2000 determines how long the pulse excites the ceramics.
The projector’s transmit pattern ensonifies the seafloor in a very wide across-track, but narrow
along-track pattern as the vessel moves along the survey line. The across-track angle is 160°; the
along-track angle depends on frequency. The 450 kHz along-track pattern is 0.9° (0.5° for the Sonic
2026). The along-track lengthens out to 2° at 200 kHz. This is the Normal Operating Mode and not
extended Vertical Mapping Mode.
Figure 140: Transmit pattern; Sonic 2024
Depending on the water conditions, seafloor composition and other factors, a portion of the
acoustic energy that strikes the seafloor will be reflected back towards the surface. The return
acoustic energy will strike the Sonic MBES receiver’s ceramics.
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