Instrumentation & Measurement Magazine 23-2 - 108

range-only localization [34] and light beacons algorithmic
combinations [35], [36].
Mapping and Sampling Systems: They monitor different areas
or the seabed by generating 2-D and 3-D operational maps employed in multiple applications, e.g., sonar technologies [37].
The main and current sensors used for this issue are detailed
in Table 1. The optical cameras often employ LED illumination due to the darkness present in submarine work, allowing
a wide range light condition [38]. The information collected by
these systems can be transferred to audiovisual documents,
providing real time remote exploration in some cases, employing techniques as submarine image processing approaches,
e.g., image de-scattering process, image high definition assessments and image color restoration [39]. The number of studies
about the optical capture and camera systems is rising due
to the importance of graphical documents for maintenance
works [40].

Features of Applied AUV Systems
One of the main advantages of AUVs is their ability to work
following a programmed route. There are several methods to
follow these routes, for example, using acoustic beacons on
the seabed, GPS location, baseline acoustic communication,
inertial navigation. It could be based on the combination of
Conductivity [41], Depth and Temperature (CDT) sensors [42],
inertial sensors and Doppler Velocity Logs (DVL) [43]. In contrast to gliders, that use a buoyancy engine and follow a wavy
path, AUVs are able to retain a linear route through the sea
[44]. For this reason, these vehicles are suitable for geoscience
applications that require a constant altitude, such as seabed
mapping and sub-bottom profiling remotely, allowing tasks in
a remote area [45].
Table 1 summarizes the main uses, properties, methods
and references of the sensory systems, doing a dissertation
between navigation and cartography mapping applications,
although the uses of groups are not exclusive. The systems
and sensors could appear in multiple commercialization
configurations.
The sensors and peripheral systems are
often combined in one
programmed functional
system to provide improved performance, e.g.,
navigation, mapping or
drive systems. Until now,
the systems implemented
in AUVs such as multibeam
echosounders (MBES) [69],
side-scan sonar (SBP) and
sub-bottom profilers (SSS),
together with the photography of the seabed, have
managed to satisfy the reFig. 4. AUV Control unit block diagram.
quirements for underwater
108	

offshore cartography [70]. However, the development of sensors is now focused on monitoring the water column. The
Natural Environment Research Council (NERC), in 2000, developed the first geochemical sensor implemented for an AUV
called Autosub, that was fitted with a manganese analyzer in
2003 [71] and 2005 [72]. These systems demonstrated that the
chemical sensors embedded in the AUV can detect variation in
small ranges of distribution of chemical elements, not resolved
by traditional sampling methods. Since then, the chemical sensors developed in the AUV for geosciences in the high seas
have been used mainly in the search for active hydrothermal plumes in the water column [73] or for detecting active
methane venting [74]. Nevertheless, the kind of navigation a
mapping system uses depends on the different operations or
mission objectives. The main considerations are the required
location accuracy and the size of the region of interest. Combining these variables can allow a higher performance in the
underwater vehicle [75], e.g., the simultaneous localization
and mapping (SLAM) technology [76].
The general approaches to solve AUV positioning and localization are based in ultrashort baseline (USBL) [77] and long
baseline (LBL) [78], and require a localized and preassigned
infrastructure. Nowadays, SLAM is focused to a dynamic
multiagent system, allowing quick flexibility and deployment
with the lowest facilities [79]. Furthermore, these techniques
developed for surface robotics applications [80] are being redeveloped for underwater uses, optimizing the navigation
design and operability of these vehicles and missions [44].
The functional outline showed in Table 1 should be correctly coupled in a complex control system. Fig. 4 shows an
example of the AUV control unit design process, considering
the aforementioned systems and developing interconnection
between different systems by a microcontroller [81]. The vehicle's primary design phase considers the interchangeable
elements, with easily extractable parts for maintenance work
and optimal space distribution.
An important challenge for AUV development are the
telecommunication technologies, due to the complexity of
the marine and submarine environment [82]. One of the key

IEEE Instrumentation & Measurement Magazine	

April 2020
Instrumentation & Measurement Magazine 23-2

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