IEEE - Aerospace and Electronic Systems - August 2022 - 37

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passive interferometers (ESM sensors), and infrared sensors
were fused [18]-[20]. In this work, the North Atlantic
Treaty Organization (NATO) Advisory Group for Aerospace
Research and Development took an important
part [21]. Gradually, more and more complex systems
were developed, where data from sensors, such as active
radars, identification friend or foe (IFF), or ESM were
combined [22], [23]. Over time, the computing power was
increasing, which could lead to the development of
bistatic radar techniques, such as forward scattering radar
and, in particular, PCL [24]. Passive radars are known for
operating without their own cooperative emitter, high
detection refresh rate (especially when utilizing omnidirectional
antenna arrays), and increased capability to
detect targets with a reduced signal-to-noise ratio (such as
stealth aircraft) [25], [26]. However, more complex mission
planning procedures should be undertaken due to
more complex signal propagation models using bistatic
geometry and illuminators of opportunity [27]. Due to
some ofthe passive radar's features, such as the high probability
of false alarm, possible ghost targets, and poor
direction-of-arrival (DoA) estimation (comparing to typical
air surveillance radars), fusing active and passive
radars' data causes high computing load. Because of that,
the first attempts to perform such fusion took place in the
twenty-first century [28]. A massive amount of work was
done by NATO Sensors and Electronics Technology
(SET) Research Task Groups (RTG), starting with NATO
SET-152/RTG called " Deployable Multiband Passive/
Active Radar for Air Defense (DMPAR) " (2009-2012). A
DMPAR concept was introduced, whose central objective
was to integrate data from active and passive radars operating
in different frequency bands [29]. Work on this data
AUGUST 2022
fusion concept was continued in two NATO groups SET195/RTG
called " DMPAR Short-Term Solution Verification "
(2013-2016) and SET-258/RTG called
" DMPAR Deployment and Assessment in Military
Scenario " (2018-2021). During work on the first group
(SET-195), in 2014, the DMPAR Evaluation Trials for
Operationally Upgraded Radar were conducted, where
active radars and passive radar demonstrators took
part [30]. Active-passive data fusion was conducted, but
in an offline manner only. During work on SET-258/RTG
(a still-active group), the Active Passive Radar Trials-
Ground-based, Airborne, Sea-borne (APART-GAS) took
place in 2019, where data fusion was conducted for operational
military scenarios [31]. Based on the active and passive
radars' plots acquired from the military network,
fusion was conducted online. During measurements,
active military radars, operational passive radars, passive
radar demonstrators, and a PET system took part. An
exhaustive data fusion, including data from all sensors,
was conducted offline after the trials. Obtained results are
presented in the further part of this work.
This article is organized as follows. In the section
" Sensors, " the main parameters of the sensors, which took
part in the APART-GAS trials and whose data have been
used in the data fusion, are described. In " Scenario
Description, " the main objectives of the trials, together
with the scenario descriptions, are presented. Furthermore,
in " Data Fusion, " the data fusion results of active and passive
sensors presented in the article are shown in detail. In
the end, the obtained results are summarized, showing the
main capabilities of the tested technology and further
direction of development in the field of active and passive
sensors.
IEEE A&E SYSTEMS MAGAZINE
37
IEEE - Aerospace and Electronic Systems - August 2022

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