Zusammenfassung
In this paper we studied the physical properties of the Gulf of Naples
(Southern Italy) for its use as a commu- nication channel for the
acoustic transmission of digital data acquired by seismic instruments
on the seafloor to a moored buoy. The acoustic link will be assured
by high frequency acoustic modems operating with a central frequency
of 100 kHz and a band pass of 10 kHz. The main operational requirements
of data transmission concern the near horizontal acoustic link, the
maximum depth of the sea being about 300 m and the planned horizontal
distance between seismic instruments and buoy 2 km. This study constructs
the signal-to-noise ratio maps to understand the limits beyond which
the clarity of the transmission is no longer considered reliable.
Using ray-theory, we compute the amplitudes of a transmitted signal
at a grid of 21x12 receivers to calculate the transmission loss at
each receiver. The signal-to-noise ratio is finally computed for
each receiver knowing also the transmitter source level and the acoustic
noise level in the Gulf of Naples. The results show that the multipath
effects predominate over the effects produced by the sound velocity
gradient in the sea in the summer period. In the case of omnidirectional
transmitters with a Source Level (SL) of 165 dB and a baud rate of
2.4 kbit/s, the results also show that distances of 1400-1600 m can
be reached throughout the year for transmitter-receiver connections
below 50 m depth in the underwater acoustic channel.
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