Fencepost
Miltec Research and Technology
Figure 1. Acoustic Fencepost (test bed sensor)
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MRT has developed the capability for detecting and tracking targets acoustically.
Initially the research was focused on tracking airborne targets, in particular high
speed low flyers (the cruise missile threat). Most recently, MRT has applied this
technology to tracking ground targets. For purposes of demonstrating this technology,
MRT developed an acoustic sensor test bed named “Acoustic Fencepost System.” A fencepost
system consists of multiple fenceposts (FP) spaced appropriate distances apart.
The individual sensors as shown in Figure 1 are called fenceposts because of the
idea of building an acoustic fence around or near an area one wishes to protect.
The original motivation for this research was to provide an early warning to radar
from a forward deployed acoustic fence. Cruise missiles and cruise missile like
threats generally have very low radar cross sections and fly very low flight profiles
making them difficult for radar to detect. The idea of the Acoustic Fencepost System
is to help augment current systems by cueing them to objects of interest just as
we as humans use our ears to cue our eyes.
Figure 2. Bearing angle output from two different fence posts.
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The Acoustic Fencepost System is a system of multiple sensor nodes each equipped
with a small five microphone array, 3-axis seismometer, GPS, electronic compass,
data acquisition, single board computer, raw data storage device, wireless data
modem, and an optional solar panel. All raw data logged is time stamped for post
analysis purposes if post analysis is desirable. The FP sensors are waterproof and
have an operating temperature range of 0° to 50° C. The current runtime
life for each sensor is 30 hours and this life can be extended with the optional
solar panel connected. The master node or base station that communicates to each
sensor monitors each FP’s activity (detection and logging states), GPS location,
inside box temperature, battery voltage, tamper alarms, and system health.
Figure 3. Acoustic track result of an air target.
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The sensor nodes or FP shown in Figure 1, acoustically and seismically detect targets
and subsequently transmit bearing vector information about the target to the master
node via their wireless data modems. Figure 2 shows acoustic bearing angle versus
time data from two different sensors for a particular flyby event. The solid curves
were produced using the acoustic data while the dashed curves were produced using
truth position data given by GPS. Hence, the solid curves would match the dashed
curves exactly if the acoustic data were perfect and noise free. It is important
to note that the acoustic bearings are extremely close to the truth data and there
is less than five degrees of error in the acoustic bearing anywhere in the time
series shown. Once the master node starts receiving bearing data from at least two
of the fenceposts, estimates of the target’s position, speed, and heading are generated
near real-time. The tracking technique used is based upon the familiar extended
Kalman filter algorithm often employed in navigation, radar-based tracking, and
feedback control applications. Track estimates are typically accurate within 10%
of range to the target. Track lengths are dependent on the source level of the target
and environmental conditions.
Figure 4. Acoustic track result of a ground target
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The technology developed within the Acoustic Fencepost System is applicable in areas of Homeland Security, perimeter or facility protection, and battlefield situational awareness. Although the system currently exists as an experimental test bed for technology demonstrations, Miltec certainly has the capability to produce a hardened field unit for production to meet customer specific needs.
For more information, please contact:
Jay Williams
(662) 281-7286
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