IEEE - Aerospace and Electronic Systems - August 2022 - 45

Fr€anken et al.
from the number of processed transmitters over the duration
of the CPI up to target-specific geometric aspects,
such as distance from transmitters and receivers, as well
as altitude. Table 1 gives some exemplary numbers,
namely the total number of updates per second (i.e. averaged
over the duration of the scenario) for Figure 13, the
number of updates per second averaged over the four
maneuvering tracks of Figure 14 and the number of
updates per second for the track in Figure 15. When computing
the latter two rates, only those segments of the
tracks have been honored where actual detection by the
respective sensor has occurred.
The fusion ofactive and passive radar data frommultiple
Figure 17.
Passive radar supports where active radar has problems due to
sparse data. Active plots and tracks (top) as well as fused tracks
and created plots (bottom). Colors as in Figure 16, positions relative
to Southern Twinvis sensor.
maneuvering aircraft at lower altitude in both figures are
clearly covered. The fact that the armasuisse sensor is
located more to the west than the one from Warsaw University
(see Figure 15) does have a certain impact though.
During the campaign, the fused data have been
reported with an external update rate of one Hertz. Internally,
the update rate based on the bistatic plot data of the
passive radar sensors was much higher. Clearly, such an
internal update rate depends on various factors ranging
sensors provides an enhanced situational awareness by producing
improved results compared to what a single sensor or
sensor type is able to produce. Figure 16 shows a scene where
passive radar is capable to fill the gap induced by the active
radar's cone of silence. As apparent from the upper image,
active radar stops to detect the airliner (flying from northwest
to south-east) for a longer time as the aircraft's altitude
then is above the maximum detectable elevation of the radar.
Consequently, the active radar track is dropped after some
bridging time. The contributions from passive radar make
sure that an uninterrupted fused track is maintained over the
gap and continued once active data becomes available again.
Especially for slowly revolving active radar, tracking
tends to become less reliable when target distance
approaches the maximum detection range, and plot data
becomes sparser. Passive radar, with its simultaneous 360
degrees of target detection, may prove to be a valuable
support in those cases, as indicated in Figure 17. Overall,
the use of passive radar probably allows us to plan future
active radar surveillance with less overlap than it is done
today. Figure 18 confirms that it is indeed possible to
extend the coverage area of active radar by supplying
Figure 18.
Passive radar extends coverage area to the South. Active plots and tracks (left) as well as fused tracks and created plots (right). Colors as in
Figure 16, positions relative to Southern Twinvis sensor.
AUGUST 2022
IEEE A&E SYSTEMS MAGAZINE
45

IEEE - Aerospace and Electronic Systems - August 2022

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