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describe the seasonal variability of the beach morphology Survey vessel and personnel for marine operations were
as completely as possible, compatibly with the timetable provided by the Marine Reserve Management Authority
of the project and suitable sea and weather conditions. (Area Marina Protetta Isole Egadi). The transducer was
Survey equipment and instrumentation are listed below: mounted at the port side of the vessel, using a flange
• Multibeam echo sounder with sidescan sonar Odom pole and an ad-hoc-designed steel framework.
Echoscan (30 beams, acoustic frequency 200 kHz, As regards the navigation project, survey lines normal to the
swath angle 90°); shoreline were adopted, oriented to North for Cala Azzurra
• Marine Differential GPS Trimble SPS461, dual and 45°N for Lido Burrone, respectively. Line spacing was
antenna, for position and heading measure; defined, considering the multibeam swath angle, in order to
• Trimble HydroPro software for survey planning and obtain, at nominal depth of 10 m, a 100% bottom coverage
navigation; with 50% overlap between parallel consecutive swath lines.
• Communication Technology GeoPro/SwanPro Overall, 30 transects were adopted for both sites, with 10 m
software for multibeam and sidescan sonar data line spacing. The orientation and spacing of survey lines is
acquisition; the result of an optimal compromise between swath angle
• Triton BathyPro, Triton ISIS Sonar and Golden and resolution of the instrument, maneuverability of vessel
Software Surfer software for data processing and and safety of navigation, and allowed to maximize the
presentation. surveyed area, also considering the bottom morphology
Figure 3 shows some of the above listed resources. and the presence of rocks and other obstacles in the
As regards compensation of measurement errors, nearshore zone.
the echo sounder is provided with a Teledyne TSS The offshore limit of navigation lines was planned in
dynamic motion sensor (DMS) for random errors due order to extend the survey beyond the depth of closure
to heave, pitch and roll. The heading information for d c of the active beach that, according to Hallermeier
yaw compensation is obtained by simultaneous GPS [22], can be estimated as follows:
acquisition at two antennas aligned along the main axis
of the vessel. Patch tests [21] were performed per each
operation day, to compensate the systematic errors due
to mounting offsets of the transducer.

In the above formula, g is the
gravitational acceleration, while
H s and T s are, respectively, the
significant wave height and
period representative of incident
wave conditions exceeded only
12 hours per year (exceedance
probability 0.137%).
Based on the statistical analysis of
incident wave climate discussed
in the next section, the values
H s(12hr) =4.55 m and T s(12hr) =9.28 s
were derived, resulting in a depth
of closure d c =8.70 m.
FIGURE 3 Main resources used for hydrographic surveys. a) Multibeam and sidescan A well-established extension
sonar transducer with dynamic motion sensor. b) Marine DGPS dual antenna of the Hallermeier formulation
for position and heading. c) Example of multibeam echo sounder and sidescan
sonar data acquisition during survey operations is to relate the depth of closure

EAI Energia, Ambiente e Innovazione 4/2015
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