Page 4 - Acoustical_underwater_2003

40 Revue d'Arrhénmétrie. 27. 2003
Fig. 6: Area ofPunta Galera: l Target (side scan sonar). Fig. 6: Zone de
Punta Galera : cible l.
Fig. 7: Area of Punta Galera: Il Target (side scan sonar). Fig. 7 :Zone
de Punta Galera: cible Il.
Fig. 8: Area of Punta Galera: III Target (sub bottom profiler). Fig. 8 :
Zone de Punta Galera : cible 111.
above all draft ( 1.2 m) of the boat pennitted to fit out
the instrumentation and to operate in a secure way to
completely cover the survey areas.
2.1.2 - Acquisition and navigation data integrated
system
Digitai data acquisition has been carried out with an
integrated system based on a Personal Computer and
managed by the acquisition/navigation SW HYDRQ® by
Trimble Navigation Ltd.
This system pennits to define, during the planning of
the mission, and therefore to execute all the procedures for
the management and the acquisition of the instrumental
data. In particular it defines the navigation pian and
gives all the graphical and numerica! infonnation about
the vessel commands; it also acquires and logs the data
measured by different connected sensors; it gives both
sequential fix of analog/digital records and the position
of sensors, corrected on the basis of the relative offsets.
2.1.3- Posilioning system
A DGPS receiver with transmission of the corrections
via radio VHF has been installed on the vessel. The
DGPS station was connected with the acquisition and
navigation system.
2.1.4 - Echosounder
The hydrographic echosounder ODOM EchoTrack
DF-3200 MKII is fonned by a contro] unit for the
instrument and calibration parameters setting (draft and
sound velocity) and measure (operative frequency: 24 or
200kHz), and a transducer. The system, due to the double
working frequency, measures the depth on the basis of
the different fcatures ofthc bottom and sea water column:
using the lowest frequency pennits the penetration of silk
sediments and has a bigger range of measure compared
to the resolution, whilst the highest frequency offers a
more precise measure in presence of silk sediment and
has a limited range compared to a better resolution.
2.1.5- MultiBeam Echo-Sounder (MBES)
SIMRAD Multibeam EM3000 is a high resolution
system which can operate on shallow water since 0.5 m
up to 200 m. The working frequency is 300 kHz. The
system is composed by a transducer, a processing unit
and a contro} station. The acoustic transducer has two
different arrays, one for the transmission and the second
one for reception. The processing unit should recognise
the bottom and assure the connection with the positioning
system, the gyrocompass and thc attitude motion sensor.
2.1.6 - Chirp
The Datasonics SIS-1 000 Seafloor Imaging System is
a fully integrated sonar system that uses advanced Chirp
technology to produce high resolution side scan sonar
images and sub bottom profilers. lt works with a limited
band signal transmission with "Linear Frequency Modu-
lation", to provide an additional 20-30 dB of dynamic
range over conventional side scan sonar and sub bottom
profiler. In ali sonar system, higher frequency content
is invariably associatcd with an increase in resolution
and, in the case of a sub bottom sonar, a decrease in
bottom penetration; in the case of a side scan sonar,
a decrease in range. Chirp technology, as implemented
in the SIS-1 000' Seafloor lmaging System reduces this
trade-off, providing both high resolution and penetration
or range.