IEEE - Aerospace and Electronic Systems - August 2022 - 42

Integrating Multiband Active and Passive Radar for Enhanced Situational Awareness
engine that has been used to produce the results presented
in the upcoming section. The three left blocks
provide the core functionality for processing and fusing
bistatic plot data originating from the passive radar sensors.
The implementation of those three blocks is
described to some detail in [35] and the references cited
therein, here, we will only shortly sketch the main functions.
Following the life cycle of an emerging target and
the corresponding track, three different processing
stages are executed by the corresponding components.
After conversion into an internal data format, bistatic
plots enter the tracking system via the bistatic plot associator
(top left). As long as no 3D tracks exist (e.g.,
after system startup), all plots are passed on to the subsequent
range/range-rate (R3) tracker (bottom left).
Based on the given range and range-rate information
(plus possibly azimuth if provided), corresponding R3
tracks are formed. This is done per sensor/transmitterpair
(FM) or per SFN (DAB or DVB-T) and helps to
reduce the number of false alarms. The track integrator
sets up correlations between the confirmed R3 tracks from
the different sources (by ellipsoid intersection), and monitors
each correlation's kinematics and quality over time (honoring
updates with bistatic plots newly associated to the R3 tracks)
and either eventually drops a correlation (if quality gets too
low) or confirms it (thus associating the R3 tracks) ifofsufficient
quality and either not in correlation conflict or found as
a solution ofa multidimensional assignment problem (which
is determined periodically). Herewith, the track integrator
produces integrated 3D Cartesian tracks that are reported to
the human-machine interface (HMI). In addition to that, they
are also sent as feedback to the bistatic plot associator that is
now able to perform a bistatic-plot-to-Cartesian-track association.
Associated plots are directly sent to the track integrator
and incorporated into the already maintained associated tracks
there. On the other hand, the range/range-rate tracker does not
receive the associated plots, and the corresponding R3 tracks
die out. Herewith, plots enter the track integrator via one path
only, avoiding double voting and significantly reducing
computational load by lowering the number of correlation
hypotheses to bemaintained.
In addition to the 3D tracks, Hensoldt's passive radar
tracking and fusion software also produces, mainly for output
purposes, Cartesian plots (so-called sensor-centric plots in
Asterix CAT15) [36]. Bistatic plots (in CAT15 denoted as
measurement plots) associated with a particular 3D track
over a certain time frame are kinematically fused to produce
Cartesian position and velocity estimates. As the measurement
errors can safely be assumed to be independent between
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