IEEE - Aerospace and Electronic Systems - October 2023 - 8

Monitoring of Critical Undersea Infrastructures: The Nord Stream and Other Recent Case Studies
adapt to component failures by changing its mode of
operation, without losing its ability to function. In order
to improve resilience, it is important to identify the most
critical nodes of networked CUIs that are most likely to
be failure points or vulnerable to attacks, and assess the
consequences. Recent research on robustness and resilience
of complex networks to failures and attacks
include, respectively, [17] and [18]. Moreover, different
models (e.g., [19], [20]) have been proposed to capture
the dynamics of cascading failures in systems characterized
by some flow (e.g., information, natural gas, electric
current) over a network. This allows us to understand the
fraction of nodes that can be removed before global connectivity
of the network is lost, how to stop a cascading
failure, and how to enhance a system's dynamical robustness.
As already anticipated in the " Critical Undersea
Infrastructure " section, considering the underwater cable
infrastructure, maritime choke points can be identified as
critical points due to their high density of cables and
maritime traffic. According to a recent analysis on security
threats and consequences for the EU [12], two key
maritime bottlenecks are the Strait of Gibraltar and the
passage between the Indian Ocean and the Mediterranean
Sea via the Red Sea, respectively. The former, connecting
the Mediterranean Sea and the Atlantic Ocean, is a
dense area used for various maritime activities including
submarine activities, with seven intercontinental cables
passing through the strait. The latter represents the core
connectivity to Asia where intercontinental cables pass
through the Egyptian mainland adjacent to the Suez
Canal to enhance the system's dynamical robustness.
Understanding and analyzing the interaction and interdependencies
among CUIs is ofutmost importance. Interdependency
is a bidirectional relationship between two
infrastructures through which the state ofeach infrastructure
influences or is correlated to the state of the other. Types of
interdependencies include the following [21].
Physical interdependencies, which arise from physical
links or connections among elements of the network.
In this context, disruptions and perturbations
in one component can propagate to other elements.
Cyber interdependencies, which occur when the
state of a component depends on data transmitted
through the information infrastructure. Such interdependencies
result from the increased use of computer-based
information systems for monitoring and
management activities (e.g., supervisory control
and data acquisition).
Geographic interdependencies, which exist between
two infrastructures when a local environmental
event can provoke changes in both of them. This
generally occurs when the components are in
close spatial proximity, e.g., infrastructures that
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cross borders or that provide cross-border services,
thus impacting the interests of different nations.
Finally, logical interdependencies, which gather all
interdependencies that are not physical, cyber, or
geographic, caused by, e.g., regulatory, legal, or
policy constraints.
LEGAL ASPECTS
The legal status of underwater pipes and cables varies
based on the legal zone in which they are located, as determined
by the United Nations Convention of the Law Of
the Sea. Within a country's territorial waters, which
extend up to 12 nautical miles from the coastline, the
country has full jurisdiction over the pipe/cable. In the
contiguous zone, which extends from 12 to 24 nautical
miles from the coastline, states have specific law enforcement
duties and obligations. Outside of these zones, particularly
in the high seas (areas outside of national
jurisdiction) as well as in the exclusive economic zones of
states (i.e., up to 200 nautical miles from a nation's coastline),
the legal status of pipes/cables and responsibility for
their protection is currently defined as " unclear " and
" ambiguous " [12], [22]. Furthermore, underwater pipes
may also be subject to additional regulations and laws
depending on the activities they are associated with and
their specific use. To make an example, oil and gas underwater
pipes may be subject to additional environmental
protection and safety-related regulations, while underwater
pipes crossing national borders (or used for international
trade) may be subject to additional international
laws and agreements.
SENSORS AND CONTEXTUAL INFORMATION
In this section, we describe different types of sensors and
technologies that are available and can be exploited for
CUIs surveillance.
COASTAL RADARS AND AIS
Among the surveillance sensors commonly used for MS,
S-band, or X-band pulse radar sensors installed along the
coastline represent a relevant and consistent source of
information [23]. However, their coverage area and maximum
range might be limited by line-of-sight propagation.
This limitation can be overcome by the installation and
employment of long-range sensors, such as high-frequency
surface-wave (HFSW) radars, which have been
considered for ship localization and tracking [24], [25],
[26], [27], [28]. Initially introduced for ocean remote sensing,
HFSW radars could dramatically increase MS coverage
by their ability to detect targets at over-the-horizon
IEEE A&E SYSTEMS MAGAZINE
OCTOBER 2023

IEEE - Aerospace and Electronic Systems - October 2023

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