The problem of detection, tracking and localization of multiple wideband sources (ground vehicles) using unattended passive acoustic sensors is considered in this paper. Existing methods typically fail to detect, resolve and track multiple closely spaced sources in tight formations, especially in the presence of clutter and wind noise. In this paper, several existing wideband direction of arrival (DOA) estimation algorithms are extended and applied to this problem. A modified version of the Steered Covariance Matrix (STCM) algorithm is presented that uses a two-step search process. To overcome the problems of existing DOA estimation methods, new wideband versions of the narrowband Capon beamforming method are proposed that use various algorithms for combining power spectra from different frequency bins. These methods are then implemented and benchmarked on a real acoustic signature data set that contains multiple ground targets moving in tight formations.

Aeroacoustic sensing is well motivated due to its passive nature and low bandwidth, and processing with array baselines of one to a few meters is well studied and useful. However, arrays of this size present difficulties in manufacture and deployment. Motivated by the desire to develop smaller, cheaper (perhaps "disposable") sensor packages, we consider performance for arrays with small baselines. The performance of angle estimation operating roughly in the [30, 500] Hz regime is limited by the observed signal-to-noise ratio (SNR) and propagation in the turbulent atmosphere. Scattering results in a reduction of spatial coherence, which places fundamental limits on angle estimation accuracy. Physics-based statistical models for the scattering have enabled prediction of network performance including detection, angle estimation, time-delay estimation, and geolocation. In the present work, we focus on angle estimation accuracy for the short baseline case. While a large aperture is desirable to improve angle estimation, the propagation produces a rolloff in the spatial coherence that ultimately degrades the performance despite increasing the array aperture. We characterize this tradeoff analytically via Cramer-Rao bounds, as a function of SNR, frequency range, sensor array geometry, and propagation conditions. The results clearly favor shorter ranges and higher frequencies when employing small array baselines.

Acoustic sensor arrays can be used effectively to enhance situational awareness and perimeter defense against small low-flying threat aircraft. In this paper, we discuss the activities of The Technical Cooperative Program (TTCP) Action Group 6 (AG6) on acoustic detection and tracking of Unmanned Aerial Vehicles (UAVs). We briefly discuss the TTCP-AG6’s mission and goals, describe field experiments conducted in the U.S., present results from data analysis and discuss current and future activities.

The acoustic emissions of a ground vehicle contain a wealth of information which can be used for vehicle classification, e.g. in the battlefield. However, features that are extracted from the acoustic measurements are time-varying and contain a lot of uncertainties, which makes the classification challenging. Since it is impossible to establish precise mathematical models to describe these variations and uncertainties contained in the features, we have applied fuzzy set and fuzzy logic theories to model and manage them, and have proposed three fuzzy logic rule-based classifier (FL-RBC) architectures -- non-hierarchical, hierarchical in parallel and hierarchical in series -- for the multi-category classification of ground vehicles. These FL-RBC architectures have been implemented based on both type-1 and type-2 fuzzy logic theories. We have also conducted experiments on our proposed FL-RBC architectures as well as on a Bayesian classifier to evaluate their performances. The experiments have shown that for this multi-category classification problem, (1) all FL-RBC architectures perform much better than the Bayesian classifier, (2) the type-2 FL-RBC architectures perform better than their competing type-1 implementations, (3) the type-2 non-hierarchical and hierarchical in series FL-RBC architectures perform the best, and (4) the performance of a classifier can be improved by incorporating decision fusion.

Sparse array processing methods are typically used to improve the spatial resolution of sensor arrays for the estimation of direction of arrival (DOA). The fundamental assumption behind these methods is that signals that are received by the sparse sensors (or a group of sensors) are coherent. However, coherence may vary significantly with the changes in environmental, terrain, and, operating conditions. In this paper canonical correlation analysis is used to study the variations in coherence between pairs of sub-arrays in a sparse array problem. The data set for this study is a subset of an acoustic signature data set, acquired from the US Army TACOM-ARDEC, Picatinny Arsenal, NJ. This data set is collected using three wagon-wheel type arrays with five microphones. The results show that in nominal operating conditions, i.e. no extreme wind noise or masking effects by trees, building, etc., the signals collected at different sensor arrays are indeed coherent even at distant node separation.

Acoustic sensing has traditionally been the preferred method for the detection and classification of ground vehicles. However, environmental conditions such as wind and rain pose a great challenge to prevent false detections and misclassifications. The recent work of McQ System Innovations has demonstrated the ability to successfully detect and classify vehicles with the fusion of seismic and magnetic sensing without false detections and only a small percentage of misclassifications. The algorithms developed were designed to detect single vehicles as well as vehicles in a convoy. Based on the classification of each vehicle, an imager can be triggered to find the best frame of the target, and store the image in onboard memory to send back to an operator display. The methodology of the algorithms designed for seismic/magnetic detection and classification of vehicles is shown, as well as results of testing the algorithms running in a remote sensor.

A low-noise micro-machined servo accelerometer has been developed for use in Unattended Ground Sensors (UGS). Compared to conventional coil-and-magnet based velocity transducers, this Micro-Electro-Mechanical System (MEMS) accelerometer offers several key benefits for battlefield monitoring. Many UGS require a compass to determine deployment orientation with respect to magnetic North. This orientation information is critical for determining the bearing of incoming signals. Conventional sensors with sensing technology based on a permanent magnet can cause interference with a compass when used in close proximity. This problem is solved with a MEMS accelerometer which does not require any magnetic materials. Frequency information below 10 Hz is valuable for identification of signal sources. Conventional seismometers used in UGS are typically limited in frequency response from 20 to 200 Hz. The MEMS accelerometer has a flat frequency response from DC to 5 kHz. The wider spectrum of signals received improves detection, classification and monitoring on the battlefield. The DC-coupled output of the MEMS accelerometer also has the added benefit of providing tilt orientation data for the deployed UGS. Other performance parameters of the MEMS accelerometer that are important to UGS such as size, weight, shock survivability, phase response, distortion, and cross-axis rejection will be discussed. Additionally, field test data from human footsteps recorded with the MEMS accelerometer will be presented.

A lightweight, tactical biological agent detection network offers the potential for a detect-to-warn capability against biological aerosol attacks. Ideally, this capability can be achieved by deploying the sensors upwind from the protected assets. The further the distance upwind, the greater the warning time. The technological challenge to this concept is the biological detection technology. Here, cost, size and power are major factors in selecting acceptable technologies. This is in part due to the increased field densities needed to cover the upwind area and the fact that the sensors, when deployed forward, must operate autonomously for long periods of time with little or no long-term logistical support. The Defense Advanced Research Project Agency’s (DARPA) Solid-state Ultraviolet Optical Source (SUVOS) program offers an enabling technology to achieving a detector compatible with this mission. As an optical source, these devices emit excitation wavelengths known to be useful in the detection of biological aerosols. The wavelength band is absorbed by the biological aerosol and results in visible fluorescence. Detection of a biological aerosol is based on the observed intensity of this fluorescence signal compared to a background reference. Historically this has been accomplished with emission sources that are outside the boundaries for low cost, low power sensors. The SUVOS technology, on the other hand, provides the same basic wavelengths needed for the detection process in a small, low power package. ECBC has initiated an effort to develop a network array based on micro UV detectors that utilize the SUVOS technology. This paper presents an overview of the micro UV detector and some of the findings to date. This includes the overall design philosophy, fluid flow calculations to maximize presentation of aerosol particles to the sources, and the fluorescence measurements.

Visidyne has long been active in using ultra-high resolution, at the sub-picometer level optical interferometry to measure physical parameters as: strains, electric fields, and refractive index changes. With support from DARPA-SPO this capability was applied to developing and demonstrating an optics, photonics based magnetometer to detect small magnetic, B-fields associated with underground activities. The motivation for the effort came from the availability of high-activity magneto-optic (MO) materials, crystals that produces large path differences between states of polarization with an applied vector magnetic field, the Faraday effect. These crystals based on e.g., Yttrium Iron Garnets (YIG) were originally developed to serve as in-line isolators or diodes to reduce feedback in laser diode powered fiber optic communication links. Using these crystals, combined with high resolution interferometry allowed us to demonstrate a magnetic field or B-field sensor that in many ways is superior to existing magnetometer concepts, optics based or otherwise, in terms of sensitivity, bandwidth and dynamic range. Small size and low power requirements are features of the sensor.

Untethered, underwater sensors, deployed for event detection and tracking and operating in an autonomous mode will be required to self-assemble into a configuration, which optimizes their coverage, effectively minimizing the probability that an event in the target area goes undetected. This organized, cooperative, and autonomous, spreading-out of the sensors is complicated due to sensors localized communication. A given sensor will not in general have position and velocity information for all sensors, but only for those in its communication area. A possible approach to this problem, motivated by an evolutionary optimization technique, Particle Swarm Optimization (PSO) is proposed and extended in a novel way. A distributed version of PSO is developed. A distributed version of PSO is explored using experimental fitness to address the coverage problem in a two dimensional area.

As a means to detect drug trafficking in a maritime environment, the Counter Narcotic Acoustic Buoy is part of an inexpensive system designed to detect "Go Fast" boats and report via satellite to a designated location. A go fast boat for this evaluation is defined as any boat with twin 200 horsepower outboard engines. The buoy is designed for deployment in salt water at depths ranging from 50 to 600 feet and can be easily deployed by one or two persons. Detections are based on noise energy exceeding a preset level within a frequency band associated with the go fast boat's acoustic signature. Detection ranges have been demonstrated to greater than three nautical miles.

The cost of thermal imaging technology has, up until now, precluded its use in networked sensor systems which require sensors to be deployed in very large numbers. Detectors based on the manufacturing processes used in the production of conventional silicon chips offer a breakthrough in cost compared to other technologies. Despite having modest performance, this technology offers a route toward a very cost-effective thermal imaging sensor for networked applications, where the limited performance of each individual sensor is less significant due to the advantage given by large numbers of sensors covering the target area. By carefully optimising the detector format, this low-cost technology is able to achieve useful performance at short ranges which are suited to a networked sensor system.

Most spectrometers used for field measurements are based on a diffraction grating to disperse light. Not only are they expensive, but they have some design setbacks as well. A prism does not have the resolving power of a grating, however, enhanced dispersion can be obtained using only a prism and a convex hyperbolic mirror. In this study, we present the design of a prism-based spectrometer, and an analytical model that represents its function. Simulations based on this model and experimental results show that a spectral sampling of 0.1 nm can be accomplished with this design. In addition to dispersion, we address the issue of linearity in the spectral domain and we present simulated and experimental results. Our design should to be cheaper, more lightweight and more light-efficient than typical grating spectrometers.

A measurement of the photoelectric parameter (contrast, pixels affected) degradation of visible Focal-Plane Arrays (FPAs) irradiated by a laser has been performed. The irradiation fluence levels applied range typically from 300 μJ/cm² to 700 mJ/cm². A silicon FPA has been used for the visible domain. The effects of a laser irradiation in the Field Of View (FOV) and out of the FOV of the camera have been studied. It has been shown that the camera contrast decrease can reach 50% during the laser irradiation performed out of the FOV. Moreover, the effects of the Automatic Gain Control (AGC) and of the integration time on the blooming processes have been investigated. Thus, no AGC influence on the number of affected pixels has been measured, and it has been revealed that the integration time is the most sensitive parameter in the blooming action. Finally, only little laser energy is necessary for the system dazzling (1 μJ for 152 ns). A simulation of the irradiated images has been developed using a finite-difference solution. A good agreement has been shown between the experimental and simulated images. This procedure can be extended to test the blooming effects of IR cameras.

We use an array of microlenses to create multiple perspectives of a 3D scene (integral image). These perspectives are captured by a camera and digitally processed to extract the distance information from the differences of parallax. We present a technique to estimate the distance of objects and to digitally reconstruct the 3D scene in a computer. We show how this digital reconstruction can be used to visualize or recognize objects in a 3D scene.

This paper describes a device that uses flow-induced electromagnetic induction as a source of continuous electrical power. The target application is energy harvesting (auxiliary power) for unmanned undersea vehicle (UUV) intelligence, reconnaissance, surveillance (ISR) operations to extend mission duration (trickle charging) or to power supplementary sensor systems. Other military/commercial applications can be envisioned as well for any system that involves the flow of low conductivity fluids and a need for low-level continuous electrical power. The basic device consists of orthogonal pairs of electrodes and a permanent magnet mounted flush with the vehicle surface. When a conducting fluid (e.g., seawater) flows over the device, an electric field is established in the fluid resulting from the motion of the conducting fluid through the magnetic field. The mean flow induced electric field in the fluid is mapped to a DC voltage across the electrode pairs by the same physical process exploited in electromagnetic flow meters. The theoretical basis for the device operation is developed here and used to determine the optimum device/array configuration and to provide numerical estimates of the available DC power. For a UUV at an operating speed of 10 knots, it is estimated that a continuous DC power level of 10mW can be obtained by a relatively compact array of these devices. Laboratory experiments and a more complete analytical model are required to develop an operational system for a full-scale UUV.

An unmanned undersea vehicle (UUV) needs an obstacle avoidance capability to make autonomous path planning decisions for successful undersea search and survey, maritime reconnaissance, communication/navigation aids, and tracking and trailing in uncharted shallow water. Physical Optics Corporation (POC) has developed a novel autonomous UUV path optimization navigator system for real-time, robust, self-adjusting, intelligent autonomous obstacle avoidance/navigation of UUVs. The POC system is based on our proprietary fast genetic algorithm, which processes signals from on-board obstacle avoidance sonar sensors to continuously optimize the navigation path while avoiding both moving and stationary obstacles in shallow waters. The system performs autonomous obstacle avoidance, accommodating navigation parameter changes. Vehicle dynamics are also incorporated by hydrodynamic compensation.

This paper presents issues related to effects generated in avionic electronics by terrestrial neutron environments and methods for mitigating the effects through part selection, circuit design and system architecture design. The paper includes an explanation of the System Hardening Upset Recovery (SHUR) technology macro cell library and demonstrates how the available functions can be applied to implement robust system operation in the presence of neutron-induced component upsets and package latchup. Recent data on electronic parts and reactor tests performed on components is presented to demonstrate the susceptibility of electronics and components to terrestrial neutrons.

This paper describes a study performed with the objective of investigating Concurrent Constraint Programming (CCP) as the main tool for the design and the implementation of a software path planner. The main features of the path planning are introduced along with some modeling and implementation issues. The CCP approach is motivated by the facility of translating complex models with domain specific features into efficient implementations. In order to use CCP, the path planning is formalized as a constraint satisfaction problem by defining variables, domains, and constraints. The proposed solution is as general as possible, and it is widely applicable in several contexts. A demo application has been implemented, and it is described in this paper. The application comes with a graphical interface that allow the user to define the mission constraints. The output of the application is a path plan, i.e. a list of waypoints that can also be displayed on a geographical map. The estimated path length, fuel consumption, and path risk are given as well.

The Homeland Defense community is increasing its focus on port security and harbor protection. Rising to the challenge, the U.S. Coast Guard is tasked with monitoring and protecting our harbors where commercial container ships enter. Tracking of the onboard containers is of great concern to the protectors of the waterfront. A system capable of identifying the number of containers onboard the vessel, when the containers are added or removed, contents of the containers, etc., will significantly reduce the potential for a security problem by providing essential information to the Coast Guard or other port security so that they can decide whether or not pre-boarding is necessary. That is, boarding the ship and inspecting the cargo while still at a safe distance from the harbor. A conceptual pictorial of this concept is shown in Figure 1. This paper presents a system that utilizes transmitters embedded on the containers which incorporate unique ID codes identifying the container, its history, and other information. A Communication/Navigation Aid (C/NA) type vehicle/buoy concept, presently being developed by Sippican (under contract to the Office of Naval Research (ONR) as part of the Autonomous Operations -- Future Naval Capabilities (AO-FNC) program, positioned at sea, would include a payload of NuWaves’ communication transceivers able to receive the cargo container’s transmitted ID and forward this information by RF link to a ground station. The Port Authority and/or the Coast Guard would then utilize the information to make an assessment of the vessel prior to port entry. Although, this paper illustrates a scenario applicable to the cargo shipping industry, it is also applicable to other homeland defense areas such as unattended open ocean force protection, drug and law enforcement, and environmental monitoring.

The Behavior Enhanced Heterogeneous Autonomous Vehicle Environment (BEHAVE) is a distributed system for the command and control of multiple Unmanned Vehicle Systems (UVS) with various sensor payloads (EO, infrared and radar) and mission roles (combat, reconnaissance, penetrator, relay) working in cooperation to fulfill mission goals in light of encountered threats, vehicle damage, and mission redirects. In its current form, BEHAVE provides UVS dynamic route planning/replanning, autonomous vehicle control, platform self-awareness, autonomous threat response, and muti-vehicle cooperation. This paper focuses on BEHAVE's heterogeneous autonomous UVS team cooperation achieved through the transformation of UVS operational doctrine into UVS team behaviors. This level of tactics provides the initial high-level cooperative control guidance and plans for multiple UVSs operating to achieve specific mission goal. BEHAVE's heterogeneous UVS behaviors include inter-vehicle cueing capability on coupled missions based on new threats, targets, and foreshadowing changes in environments, optimizing individual UVS mission roles, enhanced reassignment of mission goals based upon resources consumed and threats encountered, and multi UVS team threat behavior. Threat behaviors include logic incorporated for team scenarios such as drawing out or confusing threats.

Situation awareness is an important factor in the effectiveness of aerial missions. One of the major problems with the UAV is that human operators lack situation awareness. Limited bandwidth does not allow telepresence to a degree, which gives the same level of situation awareness that pilots of regular airplanes have. The best solution would be to equip UAV with a “situation awareness” system that in the real time provides operators with the information necessary for effective mission control and decision making, and allows effective supervisory control of the UAV. Vision in advanced creatures is a component of situation awareness, navigation and planning systems. Fast information processing and decision making requires reduction of informational and computational complexities. The brain achieves this goal using implicit symbolic coding, hierarchical compression, and selective processing of visual information. The Network-Symbolic representation, in which both systematic structural/logical methods and neural/statistical methods are the parts of a single mechanism, converts visual information into relational Network-Symbolic knowledge models, effectively resolving ambiguity and uncertainty in the visual information, and avoiding artificial precise computations of 3-dimensional models. The UAV equipped with such smart vision, will have a situation awareness system that gives operators better control over aircraft and significantly improves surveillance and reconnaissance capabilities.

Modern battlefields depend on GPS for precision navigation and timing. Unfortunately, GPS signals are very-low level and GPS interference, both intentional and unintentional, can severely degrade GPS performance. Unmanned Aerial Vehicles (UAV), which have proven their value on the battlefield, rely heavily on GPS for navigation and flight integrity. Key to continued mission success for UAVs is enhanced anti-jamming capabilities. A revealing test of anti-jamming performance for a UAV is to maintain GPS synchronization, while accurately locating a GPS jammer. A small, modular ESM payload is needed to supply anti-jamming performance for the UAV and secondarily, to use DF techniques to locate the GPS jammer. This paper investigates a small, low-power, low-cost, modular solution to reducing the vulnerability to jamming of UAVs by leveraging commercial off-the-shelf technology. A miniaturized GPS antenna configuration that both lowers susceptibility to GPS jamming, and also allows accurate determination of the GPS jammer’s location, is presented. This GPS antenna arrangement consists of two GPS antenna arrays, one positioned on the top of the UAV (facing skyward) and one positioned on the underside of the UAV (facing the ground). The top antenna array acquires and tracks a minimum of 4 GPS satellites for accurate positioning and timing. The bottom antenna array is used to detect and locate GPS interference, and in coordination with the top array, limits susceptibility to GPS interference. The first action upon detecting GPS interference is to alter the reception pattern of the top GPS antenna array to reduce the amount of interference processed by the GPS receiver. Simultaneously, sampled data from both antenna arrays are used to monitor the effect of the interference and calculate the position of the jammer.

This paper examines some of the challenges facing the community in providing radio communications to enable information systems for military operations. We believe that much of the on-going/completed work is necessary, but not sufficient, to provide the military Network Centric Operations, which integrates military’s network centric enterprise with network centric warfare. Additional issues need to be addressed to better support battle commanders as well as decider-sensor-effector linkages. We discuss a possible way ahead.

The system level hardware architecture of individual nodes in a wireless distributed sensor network has not received adequate attention. A large portion of the development work in wireless sensor networks has been devoted to the networking layer or the network communications, but considering the tight integration required between the hardware and software on each node can result in major benefits in power, performance, and usability as well. A novel hardware architecture based on the concept of task specific modular computing provides both the high flexibility and power efficiency required for effective distributed sensing solutions. A comparative power analysis with a traditional, centralized architecture gives a justifying motivation for pursuing the modular architecture. Finally, three decentralized module self-control mechanisms developed to minimize total system power will be presented and explained in detail.

Non-line-of-sight ultraviolet (UV) communication technology to support unattended ground sensor communication is described. The concept exploits atmospheric scattering of ultraviolet light to achieve modest data rates under non line-of-sight (ground-to-ground) and obstructed line-of-sight (foliage penetration) conditions. The transmitter consists of a digitally modulated UV source and the receiver employs a sharp cutoff solar-blind absorption filter coupled to a channel photomultiplier module. Prototype semiconductor UV sources with center wavelengths in the solar blind region (<280nm) already offer higher power efficiency than lasers, along with advantages in size, simplicity, and flexibility relative to both lasers and traditional mercury sources. Once commercialized, semiconductor UV sources will also offer significant cost savings over traditional gas-discharge and solid-state UV sources. In this paper, the temporal and spectral properties of a number of prototype semiconductor UV sources are presented and compared to a low-pressure mercury vapor source. Efficient modulation and data coding methods compatible with the output characteristics of both sources are discussed, and measurements from recent test bed experiments are presented.

Unattended and tactical sensors are used by the U.S. Army’s Future Combat Systems (FCS) and Objective Force Warrior (OFW) to detect and identify enemy targets on the battlefield. The radios being developed as part of the Networked Sensors for the Objective Force (NSOF) are too costly and too large to deploy in missions requiring throw-away hardware. A low-cost miniature radio is required to satisfy the communication needs for unmanned sensor and munitions systems that are deployed in a disposable manner. A low cost miniature disposable communications suite is leveraged using the commercial off-the-shelf market and employing a miniature universal frequency conversion architecture. Employing the technology of universal frequency architecture in a commercially available communication unit delivers a robust disposable transceiver that can operate at virtually any frequency. A low-cost RF communication radio has applicability in the commercial, homeland defense, military, and other government markets. Specific uses include perimeter monitoring, infrastructure defense, unattended ground sensors, tactical sensors, and border patrol. This paper describes a low-cost radio architecture to meet the requirements of throw-away radios that can be easily modified or tuned to virtually any operating frequency required for the specific mission.

Low power and small size are key features of the radio hardware associated with Unattended Ground Sensors (UGS). The RF modulation capability of the radio is an important parameter that affects overall network performance, and drives the size, cost and power consumption of both receive and transmit circuitry. This paper describes the use of a fractional-N synthesizer to directly generate various modulation waveforms at the transmit frequency. A design example is presented to highlight the benefits of this technique on a typical UHF sensor radio.

Requirements in Unattended Ground Sensor (UGS) systems have grown to include data privacy, message authentication, and anti-spoofing measures. This presents a challenge to the systems architect to consider approaches that defend against known and unknown attacks designed to compromise the system integrity. Encryption has been the preferred method to address these requirements. Encryption may be used to increase our confidence in the data transmitted in sensor networks, but requires greater, not less, attention to system security. After all, in an unencrypted network, at least we “know” that an adversary can read our data.

Unattended ground sensor systems and networked weapons systems are a major component of modern tactical military strategies. One thrust calls for increasing capability and network capacity combined with ECCM features, while lowering production prices and decreasing size and energy consumption. A second thrust calls for radio implementations that comply with the Software Communications Architecture (SCA). SCA-compliance can provide several benefits; among them are software re-use, common hardware and software platforms to reduce production cost, and upgradeability in the field. At the same time, some users and developers have raised concerns about the cost of SCA-compliance in terms of size, cost and power. This paper describes the implications of SCA-compliance and the implementation of the SCA Operating Environment for sensor data radios. In particular, we show that limited band implementations of some waveforms can be accomplished in an SCA-compliant manner with relatively small incremental increases in production cost, size and power. At the same time, a relatively significant investment is required to reach a critical mass where the appropriate "SCA-lite" architecture has been demonstrated in multiple applications.

Unatttended Ground Sensor (UGS) systems are adversely affected by the physics of RF propagation at low elevations. Units are often located at or below ground level in an effort to reduce the visual signature. Two key elements of the link budget work are compromised by the ground level antenna height: path loss and antenna gain. A two-ray reflected path model predicts that path loss increases by R⁴ with distance separating units and is inversely related to the height of the antennas. Strict adherence to this model indicates that infinite path loss is incurred by antennas located at the ground (height = 0). Ground wave propagation allows for a minimum effective antenna height to be assigned thereby eliminating this theoretical anomaly. Regardless, ground reflections for low elevation RF propagation result in up to 40 dB or more of extra path losses when compared to the free space model. Antenna modeling programs used to predict antenna patterns also paint a grim picture for UGS units. Monopole antennas have a null at the horizon and can be predicted to have antenna gains less than -20 dBi at low takeoff angles. Combining path loss and antenna gain to obtain an overall picture of the decrease in signal level is not straightforward. Simply combining the two sources of signal loss results in predicted performance that is much less than what is measured with real hardware. This paper examines the interaction of path loss and antenna gain and presents a reasonable approach for accounting for both in the link budget. Experimental results are presented to support the models.

Transmit-only ground sensor systems are inherently less complex, costly, and power-hungry than their two-way counterparts. For many applications, such as asset tracking, perimeter or border vibro-acoustic sensing, and environmental monitoring, the end-user is only interested in receiving data; there is no need to communicate with the emplaced device. In fact, many of these applications are resource-prohibitive (in cost, size, or power) unless a transmit-only solution is available. By shifting signal processing complexity away from the many distributed transmitters and into a single receiver, the system as a whole is optimized to reduce the cost for the user to monitor widespread information-gathering devices. AeroAstro's Sensor Enabled Notification System (SENS) is a satellite-based communications network that accomplishes this goal of reducing data exfiltration cost and complexity by using transmit-only remote units. Using Code Phase Division Multiple Access (CPDMA) spread-spectrum algorithms, the remote transmitters need not be synchronized or otherwise prevented from transmitting simultaneously; the central receiver can, within reasonable bounds, distinguish many transmissions "in the air" at the same time and receive all of their data. Sensors whose data can be captured into relatively infrequent burst packet transmissions, like most unattended remote sensors, are candidates for using this technology.

Applications of radio control systems involving the deployment of 100’s of devices connected to a central control point may be severely limited during certain operational scenarios unless multiple hop routing is supported. The reduction in full connectivity may be the result of a number of negative factors including local interference, hostile jamming, damage to communications equipment, or changes in environmental conditions. To counteract the potential deprecation in communications capacity the use of adjacent nodes to act as forwarders is employed to allow the network to remain fully connected. The network under consideration here is one in which the controlled elements remain mostly fixed in location though the remote control point is free to move as required during the operation of the communications network. The overall system effectiveness in a network containing both asynchronous sensors and remotely controllable munitions can be largely determined by the latency required when delivering data packets between endpoints. The ability to provide a high capacity/high data rate control channel is not always an option in deployable systems. The use of lower capacity communications channels can result in limitations when sensor/control information begins to flood the network during periods of high activity. In these situations the sending of control information to update routes based on the dynamic conditions in the network can become a drain on the network resources and must be minimized by the networking approach.

The monitoring of a diffuse process, such as the propagation of a toxic gas in an area, using the partial differential equation (PED) model via autonomous wireless sensor networks is studied in this research. Sensor nodes update the base station with their estimates of PDE model parameters rather than raw sensor measurements. Then, the base station can reconstruct the phenomenon through model parameters and initial and boundary conditions. In-network processing techniques to estimate the PDE coefficients are presented. A scheme is presented to provide a hybrid combination of decision and data fusion to find a proper tradeoff between estimate accuracy and energy efficiency. Besides, several open issues in this research context, such as identifiability of parameters, monitoring of time varying boundary conditions and unknown sources, are discussed.

In this paper we present an algorithm to determine the location of an acoustic sensor array using the direction of arrival (DOA) estimates of a moving acoustic source whose ground truth is available. Determination of location and orientation of sensor array based on the statistics of errors in the DOA estimation is a nonlinear regression problem. We formulate and derive the necessary equations to solve this problem in terms of the bearing estimates of the acoustic source and its location. The algorithm is tested against helicopter data from three acoustic sensor arrays distributed over a field.

Although touted as a revolutionary technology with a wide scope of application, the actual design and implementation of full, end-to-end wireless sensor networks (WSNs) has rarely been demonstrated. One of the primary factors holding back the field is that the capabilities of WSNs and realistic specifications of WSN applications are not well understood. Much research has been devoted to specific hardware, software, or algorithmic components of these networks with very little work having been done on full system implementation for real-world problems. The multitude of WSN components that have been developed result from different tradeoffs made among the parameters governing WSN systems. This paper introduces and analyzes these governing parameters and how tradeoffs are made among them. Ultimately, a matching metric presented helps WSN designers use specifications on these parameters to find and integrate appropriate WSN components for implementing real-world WSN solutions.

Riverside Research Institute (RRI) performed a three-month study of the sensor physics which will be useful in an urban warfare environment for the Army DCS G-2. Different phenomena were qualitatively evaluated for their utility in providing improved situational awareness and identification of specific threats and obstacles present within a city while supporting the warfighter applicable to Intelligence, Surveillance and Reconnaissance (ISR). The goal was to provide a technology investment strategy to maximize the benefit of future Measurement and Signature Intelligence (MASINT) Science and Technical Intelligence (S&IT) systems. This report summarizes the findings of the study. No single sensor program or phenomenology addresses the broad spectrum of war fighter needs within the challenging urban terrain. Understanding the user community requirements is a necessary next step in quantifying and prioritizing MASINT performance parameters to provide the FF (Future Force) a decisive advantage in urban areas.

The recent war on terrorism and increased urban warfare has been a major catalysis for increased interest in the development of disposable unattended wireless ground sensors. While the application of these sensors to hostile domains has been generally governed by specific tasks, this research explores a unique paradigm capitalizing on the fundamental functionality related to sensor systems. This functionality includes a sensors ability to Sense - multi-modal sensing of environmental events, Decide - smart analysis of sensor data, Act - response to environmental events, and Communication - internal to system and external to humans (SDAC). The main concept behind SDAC sensor systems is to integrate the hardware, software, and networking to generate 'knowledge and not just data'. This research explores the usage of wireless SDAC units to collectively make up a sensor system capable of persistent, adaptive, and autonomous behavior. These systems are base on the evaluation of scenarios and existing systems covering various domains. This paper presents a promising view of sensor network characteristics, which will eventually yield smart (intelligent collectives) network arrays of SDAC sensing units generally applicable to multiple related domains. This paper will also discuss and evaluate the demonstration system developed to test the concepts related to SDAC systems.

Networks of unattended ground sensors are fast becoming a reality, but little attention has been paid to date to the problem of how to plan an effective deployment of these sensors. Since the performance of the networked sensors depends on weather, target type, communications, terrain, and on how the sensors cooperate, the problem of planning a deployment is a very complex one. We will show how these factors can be included in a deployment planning tool that allows the warfighter to plan a deployment of acoustic sensors in near-real time. This tool can also be used as a health-monitor for the network of sensors, allowing the warfighter to maintain the network of sensors at a level of effectiveness needed to meet the mission goals.

A field test experiment sponsored by the NATO Task Group (TG-25) was conducted in France in October 2002 to demonstrate acoustic and seismic unattended ground sensor (UGS) technology. Participants from member nations were afforded the opportunity to test and benchmark the performance of various sensor systems and share performance data in a collaborative networking environment. The ARMY Acoustic Center of Excellence (ACOE) deployed three sensor platforms in support of the test; a Hand Emplaced (HE02) acoustic/seismic sensor system developed by SenTech Corporation, an in-house developed acoustic data acquisition system, and a meteorological data collection node developed by Penn State University. In this paper we describe the detection, direction finding and target counting performance of the multi-sensor suite against multiple target scenarios that consisted of various heavy, light, wheeled and tracked vehicles. The results are based on report messages that were archived via a wireless Ethernet interface and TCP/IP network system called “SPIDER” that provided real-time visualization of sensor performance and managed the collection of UGS output data at a centralized server location.

Operational trials of Textron Systems’ Terrain Commander unattended ground sensor (UGS) system are described. Terrain Commander is a powerful new concept in surveillance and remote situational awareness. It leverages a diverse suite of sophisticated unattended ground sensors, day/night electro-optics, satellite data communications, and an advanced Windows based graphic user interface. Terrain Commander OASIS (Optical Acoustic SATCOM Integrated Sensor) provides next generation target detection, classification, and tracking through smart sensor fusion of beam-forming acoustic, seismic, passive infrared, and magnetic sensors. With its fully integrated SATCOM system using internet protocols, virtually any site in the world can be monitored from almost any other location. Multiple remote sites such as airfields, landing zones, base perimeters, road junctions, flanks, and border crossings are monitored with ease from a central location. Intruding personnel or vehicles are automatically detected, classified, and imaged. Results from early operational trials in the outback of Australia and in various locations in the US are described. Probability of detection and recognition against a wide variety of targets including personnel, military and civilian vehicles, in-shore watercraft, and low altitude aircraft are discussed. Environments include snow cover, tropical savannah, rainforest, and woodlands. Experience with alternative SATCOM systems during the trials is also touched upon.

This paper describes a new concept for ultra-small, ultra-compact, unattended multi-phenomenological sensor systems for rapid deployment, with integrated classification-and-decision-information extraction capability from a sensed environment. We discuss a unique approach, namely a 3-D Heterogeneous System on a Chip (HSoC) in order to achieve a minimum 10X reduction in weight, volume, and power and a 10X or greater increase in capability and reliability -- over the alternative planar approaches. These gains will accrue from (a) the avoidance of long on-chip interconnects and chip-to-chip bonding wires, and (b) the cohabitation of sensors, preprocessing analog circuitry, digital logic and signal processing, and RF devices in the same compact volume. A specific scenario is discussed in detail wherein a set of four types of sensors, namely an array of acoustic and seismic sensors, an active pixel sensor array, and an uncooled IR imaging array are placed on a common sensor plane. The other planes include an analog plane consisting of transductors and A/D converters. The digital processing planes provide the necessary processing and intelligence capability. The remaining planes provide for wireless communications/networking capability. When appropriate, this processing and decision-making will be accomplished on a collaborative basis among the distributed sensor nodes through a wireless network.

A low-power hardware platform and a software framework to support distributed wireless sensing for unattended ground sensor (UGS) applications has been developed. This platform provides a comprehensive set of hardware capabilities needed to meet the sensing, processing, and communication requirements for UGS, including a 16-channel analog interface, a processor dedicated to managing real-time requirements, dual wireless interfaces, and a low-power system bus to enable system modularity. An open software framework based on the Linux kernel is hosted on the main system processor. This framework incorporates the tools for effectively utilizing the capabilities of the hardware platform and rapidly developing applications in a networked, embedded environment.

In case studies of recent MOUT failures, one of the most widely given reports from soldiers in the field was that MOUT environments are extremely confusing and complex. This confusion manifests itself by creating soldier-level difficulties in determining appropriate and operationally consistent responses to various fast paced and close range changes in the mission environment. Lack of commander-level situational awareness and robust commander-to-soldier communications cripple mission effectiveness. Furthermore, current military technologies are mostly unsuitable for urban terrain since they are generally intended for long range and coarse-grained operations which are uncommon in MOUT. The emerging technology of wireless sensor networks has potential to solve many current MOUT issues, and will be a vital part of the network-centric warfare discussed in relation to the Future Combat System (FCS). This paper will discuss technological enhancements and impacts to MOUT based on wireless sensor networks with specific emphasis on low-cost and disposable sensor system opportunities.

Unattended Ground Sensor Systems (UGSS) are evolving from large (physical) scale sensing and processing to microelectronic systems capable of processing sensed information and imagery in near-real time on movement of vehicles and personnel. Equipment needed by Special Operations Forces (SOF) includes remote wireless sensor suites comprised of sensor arrays of 'Motes' (magnetic, acoustic, seismic and/or micro-impulse radar), Radio Frequency (RF) relays, remote sensor controllers, with supporting long haul exfiltration, methods to visualize and analyze the information returned, and finally, a command and control capability that allows the sensors to be remotely accessed for turn on and off. This presentation will discuss the technology requirements of UGSS for the Special Operations Community in the areas of special reconnaissance, environmental reconnaissance, coastal patrol, targeting, and threat assessment. Specific emphasis will be placed on power technology, image compression, communications, micro-robotics, sensing devices and technology to include biological and chemical sensors. Self-forming sensor networks, high resolution still and motion cameras, laser systems, and data collection will also be addressed. In addition, this presentation will present a set of scenarios used in experimentation with unattended sensors.

The development of security systems based on seismic footstep detection is critical for homeland security and defense applications. The performance of these systems depends on various factors, including noise and signal levels in the real environment. This paper describes the effect of different real seismic noise sources -- such as highways, railroads, operating machinery, trees and shrubs swaying in the wind -- on seismic security system performance as these sources can be located close to the detection area. It is demonstrated that by moving away from these sources, the noise source spectra constantly change. Additionally, we present accurate results for the behavior of footstep signal reduction versus distance for a moving (walking/running) person and the seismic sensors. The effects of seismic signal summation and the noise associated with a number of sensors in environments such as ledge rock and soft earth surface is also discussed.

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.