Field studies were conducted in 2005 in Yuma, Arizona at the Yuma Proving Grounds (YPG) to document seismic signatures of walking humans. Walker-generated vertical ground vibrations were recorded using standard omni-directional 4.5 Hz peak-resonance geophones. Walker position and speed were measured using portable GPS equipment.
Collected seismic data were processed and hypothetical sensor performance predictions were made using an algorithm developed for the detection and classification of a walking intruder. Sample results for the Yuma study are presented in the form of sensor detection/classification vs. range plots, and color-coded animations of seismic sensor alarm annunciations during walking intruder tests. A perimeter intrusion scenario for a Forward Operating Base is defined that involves a walker approaching a sensor picket-line along a path exactly halfway between two adjacent sensors. This is considered a conservative representation of the perimeter intrusion problem. Summary plots derived from a binomial probability based analysis define intruder detection probabilities for different sensor spacings. For a 215 lb intruder walking in the Yuma test environment, a 90% probability of at least two walker-classified sensor detections is achieved at a sensor spacing of 140 m.
Preliminary investigations show the intruder classification component of the discussed detection/classification algorithm to perform well at rejecting signals associated with a nearby idling vehicle and normal background noise.
This paper describes development and application of a high-fidelity, seismic/acoustic simulation capability for battlefield sensors. The purpose is to provide simulated sensor data so realistic that they cannot be distinguished by experts from actual field data. This emerging capability provides rapid, low-cost trade studies of unattended ground sensor network configurations, data processing and fusion strategies, and signatures emitted by prototype vehicles. There are three essential components to the modeling: (1) detailed mechanical signature models for vehicles and walkers, (2) high-resolution characterization of the subsurface and atmospheric environments, and (3) state-of-the-art seismic/acoustic models for propagating moving-vehicle signatures through realistic, complex environments. With regard to the first of these components, dynamic models of wheeled and tracked vehicles have been developed to generate ground force inputs to seismic propagation models. Vehicle models range from simple, 2D representations to highly detailed, 3D representations of entire linked-track suspension systems. Similarly detailed models of acoustic emissions from vehicle engines are under development. The propagation calculations for both the seismics and acoustics are based on finite-difference, time-domain (FDTD) methodologies capable of handling complex environmental features such as heterogeneous geologies, urban structures, surface vegetation, and dynamic atmospheric turbulence. Any number of dynamic sources and virtual sensors may be incorporated into the FDTD model. The computational demands of 3D FDTD simulation over tactical distances require massively parallel computers. Several example calculations of seismic/acoustic wave propagation through complex atmospheric and terrain environments are shown.
The U.S. Army Engineer Research and Development Center is developing survivability planning and protective measures for base camps. One component of Base Camp Protection/Survivability is sensor-based security. Security designs must cover many configurations, ranging from forward operating bases to the equivalent of fixed facility installations, and be adaptable to changes in mission or base camp layout. Initial emphasis is on identifying sensor systems, such as unattended ground sensors, which can operate reliably at an early stage of base camp development when an intrusion detection capability must be established quickly under austere conditions. Another consideration is portability, so that sensor-secured perimeters can be readily relocated as a base camp evolves in size or configuration. In all cases, security designs will include guidance on the selection, placement, and operation of sensor systems to avoid vulnerabilities that would result when terrain, weather, system performance constraints, and detection zone features and maintenance are overlooked or ignored during the planning and implementation of sensor-based physical security.
The U.S. Army Engineer Research and Development Center Cold Regions Research and Engineering Laboratory is currently developing a human Intruder Thermal Model (ITM) for predicting the average surface temperature of an intruder. ITM provides steady-state predictions of average surface temperature. It accounts for metabolically generated heat and heat exchange with the environment via conduction, convection, perspiration and respiration. It also accounts for long and short-wave radiation exchanges with the environment, the short-wave component being extremely important to daytime surface temperature predictions. Clothing thermal properties and intruder height and weight are factored into model calculations as well.
When documenting the infrared images of targets and backgrounds it is usually necessary to place one or more sources having known surface radiances within the field-of-view of the imaging system in order to calibrate the imagery. Although a variety of commercially available thermal references (i.e. , "black bodies") exist they generally are very expensive and are not well suited for operating in the field under severe winter environmental conditions. A portable low-temperature thermal reference was recently developed at the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) to calibrate infrared images of mines and snow backgrounds in winter.
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