Thomas S. Anderson

Seismic detection algorithm and sensor deployment recommendations for perimeter security

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.

Seismic source model for moving vehicles

We develop a method for the loading of ground by moving vehicles in large finite-difference time-domain simulations of seismic wave propagation. The objective is to realistically produce two distinct types of ground loading for either wheeled or tracked vehicles in our propagation models: lower frequency loading associated with suspension dynamics and higher frequency impulsive loading associated with tire treads or wheels rolling over individual track blocks. These loading characteristics are important because field measurements show that vehicle ground forcing in both frequency bands produces seismic surface waves that networked sensors can remotely process for security applications. The method utilizes a vehicle-dynamics model to calculate a response to vehicle acceleration and ground features such as bumps; calculates forces transmitted to the ground; distributes these forces to staggered points of a finite-difference model; and simulates seismic wave propagation away from the vehicle. We demonstrate the method using bounce-and-pitch models of wheeled and tracked vehicles. We show that by carefully preprocessing force inputs, we can accurately simulate wave propagation and seismic signatures in finite-difference analyses of vehicles moving continuously over terrain.

Tracked vehicle simulations and seismic wavefield synthesis in seismic sensor systems

A finite-difference time-domain (FDTD) method models moving vehicle ground motion in 3D geologic environments, producing results similar to those from actual field experiments. Simulations provide a low-cost alternative to traditional prototype development schemes, which rely on expensive field tests.

3-D Characterization of Seismic Properties At the Smart Weapons Test Range, YPG

The Smart Weapons Test Range (SWTR) is a new facility constructed specifically for the development and testing of futuristic intelligent battlefield sensor networks within the Yuma Proving Ground (YPG), Arizona. In this paper, results are presented for an extensive high-resolution geophysical characterization study at the SWTR site along with validation using 3-D modeling. In this study, several shallow seismic methods and processing techniques were used to generate a 3-D grid of earth seismic properties, including compressional (P) and shear (S) body-wave speeds (V p and V s ), and their associated body-wave attenuation parameters (Q p and Q s ). These experiments covered a volume of earth measuring 1500 m × 300 m × 25 m deep (11 million cubic meters), centered on the vehicle test track at the SWTR site. The study has resulted in detailed characterizations of key geophysical properties. To our knowledge, results of this kind have not been previously achieved, nor have the methods developed for this effort been reported elsewhere. In addition to supporting materiel developers with important geophysical information at this test range, the data from this study will be used to validate sophisticated 3-D seismic signature models for moving vehicles.

FDTD Seismic simulation of moving battlefield targets

Long duration finite-difference time domain (FDTD) simulations of seismic wave propagation from spatially and time varying sources are necessary to produce synthetic data of ground motion, data that is required for the development of unmanned ground sensor systems, which are the next wave in modern battlefield technology. We have generated data from moving synthetic sources that are typically found in a battlefield scenario, a generic representation of a moving tracked vehicle and a running human. The computational approach and requirements for the long-duration simulation including the geologic model, the moving vehicle force algorithm, the resulting particle velocity wave fields, and example applications of the data are discussed.

Seismic Propagation from Activity in Tunnels

Dynamic mechanical activity in a tunnel can be measured as ground vibrations at offset distances. These signals can be processed in sensing algorithms for detection, location, and discrimination of the activity. The objective of this work is to demonstrate that seismic simulations can reveal the effect of the environment on seismic energy as it propagates from tunnels. Using massively parallel high-performance computers, the work applies a finite-difference solution to the equations of motion and isotropic stress-velocity for viscoelastic seismic propagation. Results from simulations in open, urban, and mountainous terrain reveal the nature of seismic waves as they propagate from tunnel-digging pulses and harmonic sources. Measures of relative energy and signal cross correlation provide maps that reveal locations of optimal sensing. We demonstrate applications of beam forming to monitor tunnel activity, and conclude that the simulation method produces realistic wave-field data for virtual trials of sensing algorithms

Technical validation of high-fidelity seismic signature simulations in support of FCS network ground sensors

We use detailed dynamic mechanical systems models to generate ground vibrations specific to a vehicles suspension and dimensions. These complex force distributions provide input to seismic propagation models running on massively parallel HPC computers, and result in vehicle-specific signatures. The model output is the ground response of the target traversing a complex 3D geologic region. In order to achieve scales that are useful to sensor system development, single calculation run times can exceed 70k CPU-h. Situational awareness is critical to achieving and maintaining battlefield superiority. Given the complex and dynamic environmental conditions of the battlefield, a spectrum of sensor assets are required to provide necessary information with appropriate levels of reliability. Unattended ground sensors (UGS) exploit seismic waves generated from moving targets and provide critical nonline of sight tracking and classification information. In order to develop robust ground sensor systems, systems must be developed that can adapt to the complex geologic environment. We use HPC computational resources to accurately model target specific ground motion in realistically complex geological environments. In turn, we use our simulation results to rapidly develop systems algorithms for keystone FCS subsystems including Intelligent Munition System (IMS), Tactical Unattended Ground Sensors (T-UGS), and Network Sensors for the Objective Force ATD (NSfOF). An excellent match of signals is achieved in both the time and frequency domain for our simulations of several vehicles. The data fidelity achieved replicates target specific signature features observed in field data. The level of detail in our synthetic results is sufficient to permit direct application of synthetic data to system algorithm development and engineering trade studies. Further, these data products may be used as a planning tool for optimal location of seismic UGS to maximize sensor performance (e.g., hill vs. Valley). Lastly, reliance on HPC simulations of this nature provides a low cost alternative to the traditional prototype development schemes that rely exclusively on expensive field tests.

High-fidelity simulation capability for virtual testing of seismic and acoustic sensors

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.

Unmanned Tunnel Exploitation

Tunnels are an increasing problem for securing the borders. Due to hazards inherent in assessing these tunnels, robotic reconnaissance would play an important role in gathering vital information regarding tunnel use and closure logistics. Since conventional robotics platforms do not meet the threat needs, the Unmanned Tunnel Exploitation (UTE) research used numerical simulation and experimentation to determine the optimal platform to help overcome identified technology shortfalls by addressing mission specific tasking for autonomous navigation intelligence. To refine the tunnel mission specific behaviors for UGVs, in December, 2008, testing was performed through a border tunnel in Douglas, AZ with the INL RIK laser mapping capability and associated semi-autonomous behaviors on a Foster-Miller Talon robot. The laser mapped data combined with video provided a more complete situational awareness for robot operator. In March 2009, the untethered radio communications of the Talon were evaluated in a metal-reinforced tunnel complex.

Seismic array monitoring of mortar fire during the November 2005 ARL-NATO TG-53 field experiment at YPG

The U.S. Army Corps of Engineers Engineer Research and Development Center (ERDC) participated in a joint ARL-NATO TG-53 field experiment and data collection at Yuma Proving Ground, AZ, in early November 2005. Seismic and acoustic signatures from both muzzle blasts and impacts of small arms fire and artillery were recorded using seven seismic arrays and three acoustic arrays. Arrays composed of 12 seismic and 12 acoustic sensors each were located from 700 m to 18 km from gun positions. Preliminary analysis of signatures attributed to 60-mm, 81-mm, and 120-mm mortars recorded at a seismic-acoustic array 1.1 km from gun position are presented. Seismic and acoustic array f-k analysis is performed to detect and characterize the source signature. Horizontal seismic data are analyzed to determine efficacy of a seismic discriminant for mortar and artillery sources. Rotation of North and East seismic components to radial and transverse components relative to the source-receiver path provide maximum surface wave amplitude on the transverse component. Angles of rotation agree well with frequency-wavenumber (f-k) analysis of both seismic and acoustic signals. The spectral energy of the rotated transverse surface wave is observable on all caliber of mortars at a distance of 1.1 km and is a reliable source discriminant for mortar sources at this distance.