EurOCEAN 2000 - Vlaams Instituut voor de Zee

The way to sense the marine environment acoustically in the project, has advantages over the
classical echo sounding procedures, where the angle of incidence during sea trials remains
difficult to control. Therefore, two arrays are foreseen. A vertical down looking one
(monostatic) and a second one (bistatic), which allows enhanced control of the zone to be
insonified during the trials. It is envisaged that the second one will act like a looking glass,
which can be moved over the sea bed, whereas the first one is used to deliver raw data
representing the sea bed condition, such as the bathymetry and estimates of the sedimentation
layers (rough measurements of the number of layers, thickness, etc.). This is used as a priori
information in the system identification tasks to ensure fast convergence and minimisation of
the modelling errors.
RESULTS OBTAINED
At this stage of project, some obvious results are already obtained from the partners involved in
the SIGMA project, e.g.:
1. Equipment development:
• Development of a steerable parametric array (Loughborough University group): A
system has been designed and manufactured to include a facility allowing longer
pulses of any reasonable type to be projected into the water. New software has been
developed to allow dynamic stability of the beam and to allow received backscatter
data to be captured and to be fully integrated into the GIS system. The system,
together with the new software, was available for the first sea trials and improved for
the second and third sea trials. Further development has continued on a new
commercially viable replacement for the present transmission array to allow full twoaxis
steering of the beam. The system has been tested with dynamic stability and the
preliminary analyses of the effects of this system have shown positive results.
• Development of a vertical parametric array (Technical university of Denmark): The
vertically-looking parametric acoustic array has been designed and developed, and an
estimation of its operational capabilities has been worked out. It comprises four
elements (Channel Industries PZT type 5800), each having a transmitting surface area
of 15 x 15 cm2 and operating at a fundamental primary frequency of nearly 60 kHz,
thus permitting a difference frequency in the region of 3-6 kHz.
• Development of a hydrophone streamer and positioning (CPE - Lyon: Laboratoire
d’Acoustique Systèmes, Signaux et Sonar): A hydrophone streamer and the positining
system have been designed and manufactured at the beginning of the project in order
to collect sea bottom echoes from the steerable parametric array (SPA).
• Improvement of a high resolution seismic system (GEODIA): A high resolution
seismic spread has been operated during the second sea trial. P-wave acquisition with
a penetration of 5 meters below seabed along lines where sampling has been
performed during the second sea trial. Results will be the definition of the P-wave
velocity profile over the top 5 meters of the seabed, which matches the estimated
penetration of the acoustic methods operated in the frame of SIGMA by LU and TUD.
2. Modelling and tank experiments:
• Oblique and rough interfaces (FORTH: Foundation for Research and Technology): An
algorithm for the calculation of the reflection coefficient in cases of oblique interfaces
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