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 After several decades of rather obscure awareness in
military operations, the use of passive sensors for remote battlefield
applications is becoming more popular. Driven by modern Digital Signal
Processing (DSP), sensors are become smaller, yet much more accurate
and sophisticated. These technological advances have made the
development of advanced, multi-sensor Unattended Ground Sensors (UGS)
possible. Existing in various sizes and forms, UGS contain several
sensor technologies, deployed at the area of operation, detecting,
classifying and reporting target information via wireless links to a
remote control center. UGS systems use small, low cost and robust
sensors expected to last in the field for weeks or even months. Other
systems are providing communications, processing, as well as target
verification and identification services.
 UGS systems utilize a combination of detectors, including
seismic detectors (geophones), used to identify ground vibration
caused by vehicles or pedestrians. Magnetic detectors monitor movement
of metal objects such as weapons or vehicles. Acoustic sensors are
used to detect targets by specific acoustic signatures (noise of
engine, tracks etc) while passive infrared (PIR) sensors detect
movements of objects in a narrow field of view. Input from all these
detectors is collected by the gateway, processed by its on-board
signal processors. When signatures are correlated into verified target
detection, an alarm is triggered and transmitted automatically by
radio to a central monitoring point in order to alert reaction forces
on the suspect area.
 In certain situations, other sensors are required to
verify an alarm triggered by non-imaging sensors. Such verification
will most commonly utilize an imaging sensor. A typical configuration
of such system is the Rheinmetall Defense BSA. A similar function can
be provided by the Covert Unattended Ground Imager, (UGI-C). This man
portable, persistent all-weather system is comprised of a thermal
camera triggered by PIR, taking snapshots of nearby motion events. The
captured images are compressed and sent as short 3.5 animation movies
over non-line-of-sight RF communications link. Other systems currently
available include Terrain Commander, which can be operated
autonomously or by remote control. Other topics covered
in this feature include:
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