IEEE - Aerospace and Electronic Systems - October 2023 - 3

In This Issue -Technically
MONITORING OF CRITICAL UNDERSEA INFRASTRUCTURES: THE NORD STREAM
AND OTHER RECENT CASE STUDIES
The explosions on 26 September 2022, which damaged the Nord Stream gas pipelines,
have highlighted the need and urgency of improving the resilience of critical
undersea infrastructures (CUIs). Comprising gas pipelines and power and communication
cables, these connect countries worldwide and are critical for the global
economy and stability. An attack targeting multiple of such infrastructures could
potentially cause significant damage and greatly affect various aspects of daily
life. Due to the increasing number of CUIs, existing underwater surveillance solutions,
such as autonomous underwater vehicles or remotely operated vehicles, are
not adequate enough to ensure thorough monitoring. We show that the combination
of information from both underwater and above-water surveillance sensors enables
achieving seabed-to-space situational awareness (S3A), mainly thanks to artificial
intelligence and information fusion methodologies. These are designed to process
immense volumes of information, fused from a variety of sources and generated
from monitoring a very large number of assets. The learned knowledge can be
used to anticipate future behaviors, identify threats, and determine critical situations
concerning CUIs. To illustrate the capabilities and importance of S3A, we
consider three events that occurred in the second half of 2022: the aforementioned
Nord Stream explosions, the cutoff of the underwater communication cable
SHEFA-2 connecting the Shetland Islands and the U.K. mainland, and the suspicious
activity of a large vessel in the Adriatic Sea. Specifically, we provide analyses
of the available data, from automatic identification system and satellite data,
integrated with possible contextual information, e.g., bathymetry, patterns-of-life,
weather conditions, and human intelligence.
EFFICIENT TRANSMITTER SELECTION STRATEGIES FOR IMPROVED INFORMATION
GATHERING OF AERIAL VEHICLE NAVIGATION IN GNSS-DENIED ENVIRONMENTS
Aerial vehicle navigation in global navigation satellite system (GNSS)-denied environments
by utilizing pseudorange measurements fromMterrestrial signals ofopportunity
(SOPs) is considered. To this end, the aerial vehicle is tasked with choosing K < M
most informative terrestrial SOPs. Two computationally efficient, but suboptimal,
transmitter selection strategies are proposed. These selection strategies, termed opportunistic
greedy selection (OGS) and one-shot selection (OSS), exploit the additive, iterative
properties of the Fisher information matrix (FIM), where OGS selects the most
informative transmitters in finite iterations, while the OSS selects in one iteration.
Monte Carlo simulation results are presented comparing the OGS and OSS strategies
versus the optimal (exhaustive search) selection strategy, where it is concluded that
OGS performs closely to the optimal selection, while executing in a fraction of the
optimal selection's time. Experimental results are presented of a U.S. Air Force highaltitude
aircraft navigating without GNSS signals in: 1) a rural region and 2) a semiurban
region. The performance of the aircraft's navigation solution with the selected
SOP transmitters via optimal, OGS, OSS are compared over a flight segment where
the selection remained valid. The position root-mean-squared error with the optimal,
OGS, and OSS were 4.53, 6.28, and 7.13 m in the rural region; and 5.83, 6.08, and
6.70 m in the semiurban region for an aircraft traversing a trajectory of 1.48 and
1.22 km, respectively.
OCTOBER 2023
IEEE A&E SYSTEMS MAGAZINE
3

IEEE - Aerospace and Electronic Systems - October 2023

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