EurOCEAN 2000 - Vlaams Instituut voor de Zee

DESIGN OF EXPERIMENTAL EQUIPMENT
The first sea experiment required the deployment of two transmitter units and one, somewhat
more structurally complex, receive unit. Once deployed both transmit units operated
autonomously. The receiver structure was in continual contact, via cables, to a second support
vessel. This vessel contained equipment for the recording and on-line analysis of received
data. Both transmit units were powered by internal battery sources. These required daily
replacement, thus it was necessary to recover each transmitter at the end of each day’s
experimentation and replace them on the seabed at the start of the next day’s activities. The
receiver system was left on the seabed for the whole of the experimental period (7 days), with
cable recovery from a buoy at the start of each day. The carrier frequency of the transmitter
was set to 9.5 kHz with a bandwidth of 2 or 4 kHz. The 4 kHz bandwidth was used for close
range experiments while the 2 kHz bandwidth was used for the long range experiments.
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As described, the first sea trials were used to acquire and store data from the array of
hydrophones. Input data was sourced from two sea bed mounted nodes transmitting data
simultaneously. In the second sea experiment, it is envisaged that two basic network protocol
structures will be tested by upgrading the seabed node to have both transmit and receive
capabilities. The first network will involve three nodes in a straight line, to form a basic
repeater network. The second network will see the three nodes placed in a triangular network.
TRANSMIT SCENARIO
Off-line signal processing and analysis has been performed in order to determine both the
quality of the data acquired during the first sea experiment and to assess the efficacy of the
DS/CDMA multi-access algorithm [2]. Due to the constraints of space, we report the findings