8 hydrographic survey
➠
Until recently, scientists have used methodologies with TS SEMANTIC GESMA, for defence purposes, the
based on diving and capturing video images in their study aim was to detect mines hidden in the vegetation. Several
areas. Current technology has improved the qualitative systems were combined to cross-correlate the signals
and quantitative research capabilities, and the application from different types of bottoms (sand with and without
of different hydro acoustic detection systems provides a plants, rocks) with samples obtained at different depths
variety of information. and with different settings of the systems (transmit power
Documents published by the European Acoustics and pulse length between them).
Association, highlighted the excellent results obtained in Acoustic systems combined in this test were: a side
detecting and classifying seabed vegetation by combined scan sonar; the GeoAcoustics shallow water wide swath
application of acoustic methods. They combined a single bathymetry system GeoSwath Plus, which simultaneously
beam echosounder, which enables classification of the acquires bathymetry with a swath width of 12 times
seafloor and its vegetation, a multi-beam sonar, which the water depth and geo-referenced side scan data; the
generates micro-relief, and a side scan sonar, imaging scientific high-precision echosounder Simrad EK60.
the seafloor reflectivity and thus enabling the spatial The side scan sonar shows the reflectivity of the
classification of seafloor types and vegetation. seafloor and discriminates areas where there are
The data from these systems are merged and plants or sand. The GeoSwath Plus system provides
processed, resulting in 3D images of the same quality bathymetry and geo-referenced side scan data. Both
and precision as found in the field of biomedicine. datasets can be merged to generate a three dimensional
Quantitatively speaking, this technology can work image representing the bathymetry and backscatter
simultaneously with oceanographic parameters. of the seafloor. This feature allows us to correlate the
As for the quantitative method, prospecting new three-dimensional data with the location and extent of
technologies allow a wide area of study while minimizing Posidonia meadow areas.
data collection time. Thanks to the digital storage of all The scientific probe records the acoustic pulses to
data acquired during the survey, one can make historical generate a profile of the seafloor. These data are recorded
databases that allow monitoring of the expansion simultaneously with the D-GPS position. Since the
or reduction in the length of the field of underwater sandy areas and vegetation meadows provide different
flora. You can also study how quality varies over time signatures, by applying the algorithm analysis, it
by comparing contemporary data with the previous discriminates between different types of seafloor. In this
sampling. first phase, it detects the presence of Posidonia. In that
In an experiment conducted in France collaboration case the system estimates its height and abundance.
The presence of Posidonia is limited to the depth to
which sunlight reaches, the photic zone, so most of these
studies are conducted in shallow water. This combined
with the high resolution of the acoustic systems,
generates maps that resemble virtual reality. This
methodological concept corroborates that the innovations
technology offers give high performance and ensure
scientists new and improved ways to study. Moreover,
these technologies enable the direct study of large
areas with very high resolution, whereas the traditional
approach of visual sampling was limited to very small
zone and therefore the use of statistical extrapolation.
The GeoSwath Plus sonar allows wide swath
multibeam bathymetry and side scan data to be collected
from small vessels of opportunity in water depths up to
200m beneath the transducers.
The system was designed to meet the need for a wide
swath system capable of high productivity surveys in very
shallow waters, and can achieve swath widths over 12
times water depth. The GeoSwath provides high accuracy,
high resolution bathymetry (depth measurement accuracy
exceeding the latest IHO specifications), and co-registered
side-scan data. GeoSwath versions are available for
Fig. 2. The three technologies, wide swath bathymetry, mounting on vessels of opportunity, jet skies, ROVs and
side scan sonar and single beam echosounder working AUVs. l
simultaneously. Using a GeoAcoustics GeoSwath Plus
makes the use of a separate side scan sonar obsolete as GeoAcoustics Ltd is based in Great Yarmouth, UK.
it acquires geo-referenced side scan data. www.geoacoustics.com
www.engineerlive.com
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