We consider the search for moving targets over large areas using a network of fixed sensor nodes. The concept of track-before-detect is defined and used to both manage the information between sensors ...and reduce the likelihood of false searches. We develop expressions for the probability of search success and the probability of reporting false search in this system concept. Using these as performance measures, we examine how the track-before-detect search strategy impacts design choices in these networks, by showing which parameter changes in the sensor design have the greatest impact on improving the desired performance goals.
The problem of cooperative track detection by a dynamic sensor network arises in many applications, including security and surveillance, and tracking of endangered species. Several authors have ...recently shown that the quality-of-service of these networks can be statically optimized by placing the sensors in the region of interest (ROI) via mathematical programming. However, if the sensors are subject to external forcing, such as winds or currents, they may be rapidly displaced, and their quality-of-service may be significantly deteriorated over time. The novel approach presented in this paper consists of placing the sensors in the ROI based on their future displacement, which can be estimated from environmental forecasts and sensor dynamic models. The sensor network deployment is viewed as a new problem in dynamic computational geometry, in which the initial positions of a family of circles with time-varying radii and positions are to be optimized subject to sets of algebraic and differential equations. When these equations are nonlinear and time-varying, the optimization problem does not have an exact solution, or global optimum, but can be approximated as a finite-dimensional nonlinear program by discretizing the quality-of-service and the dynamic models with respect to time. Then, a near-optimal solution for the initial sensor positions is sought by means of sequential quadratic programming. The numerical results show that this approach can improve quality-of-service by up to a factor of five compared to existing techniques, and its performance is robust to propagated modeling and deployment errors.
We propose a new approach to forming an estimate of a target track in a distributed sensor system using very limited sensor information. This approach uses a central fusion system that collects only ...the peak energy information from each sensor and assumes that the energy attenuates as a power law in range from the source. A geometrical invariance property of the proximity of the distributed sensors relative to a target track is used to generate potential target track paths. Numerical simulation examples are presented to illustrate the practicality of the technique.
Conventional delay-and-sum beamforming employs element shading weights that are derived from linear aperture approximations. For many conformal arrays, the aperture of interest is not well ...approximated by the linear assumption. In this letter, an analytical method for approximating desired linear array beampattern characteristics on a conformal array is presented. The advantage of the method is that array designers can apply rules of thumb learned from linear arrays to conformal arrays without significant degradation in performance. Many of the limitations of using conventional beamforming on conformal array surfaces can be removed by applying the method.
A numerical optimization technique that uses sonar array noise measurements is used to determine conventional shading weights that maximize the broadband deflection coefficient at the output of the ...optimal square-law detector, across a frequency band of interest. This process maintains the structure of the conventional processor while providing performance improvement typical of adaptive techniques. The performance of the optimized time domain delay-and-sum beamformer is compared with that of the traditional beamformer that uses conventionally chosen shading weights. Application of this method to conformal velocity sonar array data is shown to provide large improvements in performance over heuristic designs.
For distributed sensor technologies whose costs are understood (or which may be estimated in some reasonable manner), we derive a simple analytic means by which to estimate the most cost-effective ...sensor detection range. Specifically, we consider design of sensor nodes whose purpose is to exploit a set of coherent acoustic array technologies to detect a target with a specified radiated signature in an environment characterized by the sonar equation. We define a simplified calculus of distributed search that exploits simple target motion as a means to enhance spatial coverage for a sparse field of uniformly distributed sensor nodes. We examine this strategy in the context of both area (two-dimensional) and volume (three-dimensional) surveillance coverage under both cylindrical and spherical spreading models. In all situations, cost-effective design guidance is given based on maintaining spatial detection coverage
In this paper we present an analytical model for incorporating navigational error into a search performance prediction algorithm through the construction of a corresponding utility function. The ...search space is partitioned into a set of cells over which a utility function formulation is developed for each. The navigational displacement error is assumed to be driven by a Mixed Ornstein Uhlenbeck stochastic process. The evaluation method is based upon our previous work on utility functions as perturbative forms on Bayesian recursion models for search effectiveness modeling with non-trivial dependencies. This paper presents the development of the cell-based probability recursions for the spatially correlated navigational error. From these, a sequential formulation for utility update is developed.
In recent years the role of unmanned searchers in undersea search operations has been a topic of considerable interest. In particular, the use of multiple UUVs in the search for stationary or slow ...moving targets has raised a number of new research questions, one of which is how to effectively plan search operations. In this paper we develop a planning approach to improve trade-offs between search coverage and false search rates for a group of unmanned searchers operating in a bounded region of interest. This important trade-off is typically handled by setting an overall constraint on searcher false alarm rate and partitioning the search region among the individual search assets. We show that this non-collaborative coverage approach can be improved upon by allowing overlap in the areas of responsibility of the searchers, driven by increased sweep widths and independent confirmation requirements on target detection. Standard computational models for acoustic detection performance for the individual searchers are utilized as a function of detection threshold to control the trade-off between searcher sweep rate and searcher false alarm rate. Parametric explorations of the resulting system performance model are used to illustrate the design dependencies in numerical examples.
This paper establishes plausible limits on search performance for a set of AUVs participating in a coordinated undersea search operation. We build on previously developed cell based methods for ...evaluating search performance under conditions of geospatial non-homogeneity in detection likelihood and search object placement. To establish performance bounds, a theoretical template provided in the communications channel is adapted for development of an analogous AUV search channel. The concept of search capacity is introduced and developed in this paper. From a simple cell search capacity, search channel configurations are devised to suit specific search performance objectives and to demonstrate the generality of the performance bound when applied to search. This information theoretic performance measure is shown to support decomposition over search subspaces allowing for plausible inference in AUV search planning and post operation evaluation under geospatial non-homogeneity. Results are presented to demonstrate the validity of the performance bounds and their inherent capability to measure the collaboration potential among searchers.
In this paper we explore design issues in the deployment of distributed sensor networks (DSNs). In particular, the search performance of a notional surveillance network, and its dependence on sensor ...placement (for a fixed number of sensors) is studied. We describe a search objective for systems of sensors that utilize spatio-temporal techniques to combine individual sensor detections (which are spatially consistent with expected target behavior) in order to determine target existence in the field (track coverage). We utilize this objective in a genetic algorithm to optimize the search coverage as a function of the sensor density within a fixed search region. Target dynamics are treated as parameters with associated probability distributions, and enter the search objective as random parameters. We present several examples of optimal placement given target dynamics and sensor characteristics.
