The tracking and state estimation community is broad, with diverse interests. These range from algorithmic research and development, applications to solve specific problems, to systems integration. Yet until recently, in contrast to similar communities, few tools for common development and testing were widespread. This was the motivation for the development of Stone Soup - the open source tracking and state estimation framework. The goal of Stone Soup is to conceive the solution of any tracking problem as a machine. This machine is built from components of varying degrees of sophistication for a particular purpose. The encapsulated nature and modularity of these components allow efficiency and reuse. Metrics give confidence in evaluation. The open nature of the code promotes collaboration. In April 2019, the Stone Soup initial beta version (v0.1b) was released, and though development continues apace, the framework is stable, versioned and subject to review. In this paper, we summarise the key features of and enhancements to Stone Soup - much advanced since the original beta release - and highlight several uses to which Stone Soup has been applied. These include a drone data fusion challenge, sensor management, target classification, and multi-object tracking in video using TensorFlow object detection. We also detail introductory and tutorial information of interest to a new user.
This paper documents initial work into the development of a novel framework for sensor resource management: the
Adaptive Horizon Sensor Management Framework (AHSMF). The concept at the core of AHSMF is that the optimal
length of the planning horizon is dependent on the accuracy with which one can predict actual future performance, which
is itself dependent on the level of uncertainty in the system (e.g. target state uncertainty). In the simplest case, in which
there is no uncertainty (e.g. the target state and behavior are precisely known), a Dynamic Programming approach allows
the planning horizon to extend far into the future as it is known precisely what the long-term impact of actions will be.
However, we argue that in highly uncertain environments, the planning horizon should remain relatively short as the
implications of actions on medium (and longer) term performance are hard to quantify.
The basis of this paper is to validate this concept. We present two examples. The first is a simple toy problem in
which we must plan over two time steps. We show that one step-ahead planning can perform better than two step-ahead
planning if (i): the future impact of actions is highly variable, and (ii): the system controller has only limited information
that does not capture this variability. The second example considers the problem of tracking a highly manoeuvring target
using unmanned air vehicles (UAVs) that perform passive sensing. In this case, even more complex mechanisms influence
the optimal length of the planning horizon. Two step-ahead planning outperformed one step-ahead planning (in terms of
tracking accuracy) in many scenarios. However, in the most difficult, challenging and uncertain problems, with just one
UAV tracking a target that frequently manoeuvred, one step-ahead planning was shown to perform significantly better.
Future work will aim to identify the exact mechanisms responsible for the sub-optimality of multi-step-ahead planning in
this, and other, pertinent applications. This will then provide a framework for adjusting the planning horizon online, in
order to avoid unnecessary over-planning and maximize performance.
The Multiple Airborne Sensor Targeting and Evaluation Rig (MASTER) is a high fidelity simulation environment in
which data fusion, tracking and sensor management algorithms developed within QinetiQ Ltd. can be demonstrated and
evaluated. In this paper we report an observer trajectory planning tool that adds considerable functionality to MASTER.
This planning tool can coordinate multiple sensor platforms in tracking highly manoeuvring targets. It does this by
applying instantaneous thrusts to each platform, the magnitude of which is chosen to gain maximum observability of
the target. We use an efficient search technique to determine the thrust that should be applied to each platform at each
time step, and the planning horizon can either be one-step (greedy) or two-step. The measure of performance used in
evaluating each potential sensor manoeuvre (thrust) is the posterior Cramer-Rao lower bound (PCRLB), which gives the
best possible (lowest mean square error) tracking performance. We exploit a recent novel approach to approximating the
PCRLB for manoeuvring target tracking (the "best-fitting Gaussian" (BFG) approach: Hernandez et al., 2005). A closed-form
expression gives the BFG approximation at each sampling time. Hence, the PCRLB can be approximated with a very
low computational overhead. As a result, the planning tool can be implemented as an aid to decision-making in real-time,
even in this time-critical airborne domain. The functionality of MASTER enables one to access the performance of the
planning tool in a range of sensor-target scenarios, enabling one to determine the minimal sensor requirement in order to
satisfy mission requirements.
Typically, the posterior Cramer-Rao lower bound (PCRLB) is the performance bound of choice in tracking
applications. This is primarily due to the availability of a computationally efficient recursive formulation of the
bound. It has been shown, however, that this bound is weak in certain applications. Weiss-Weinstein lower bound (WWLB) is another second-order error bound that is free from the regularity conditions and it is applicable in a wide range of problems. In addition, it has free variables that can be tuned to get tighter bounds. In this paper, we develop the WWLB for maneuvering target tracking. In particular, we utilize the ability of the WWLB to handle continuous and discrete random variables: target motion model is represented by a separate discrete variable and the bound is calculated over the continuous state and discrete motion model variables. The bound is tightened by optimizing with respect to the free variables.
In this paper, we consider the problem of sensor resource management in decentralized tracking systems. Due to the availability of cheap sensors, it is possible to use a large number of sensors and a few fusion centers (FCs) to monitor a large surveillance region. Even though a large number of sensors are available, due to frequency, power and other physical limitations, only a few of them can be active at any one time. The problem is then to select sensor subsets that should be used by each FC at each sampling time in order to optimize the tracking performance subject to their operational constraints. In a recent paper, we proposed an algorithm to handle the above issues for joint detection and tracking, without using simplistic clustering techniques that are standard in the literature. However, in that paper, a hierarchical architecture with feedback at every sampling time was considered, and the sensor management was performed only at a central fusion center (CFC). However, in general, it is not possible to communicate with the CFC at every sampling time, and in many cases there may not even be a CFC. Sometimes, communication between CFC and local fusion centers might fail as well. Therefore performing sensor management only at the CFC is not viable in most networks. In this paper, we consider an architecture in which there is no CFC, each FC communicates only with the neighboring FCs, and communications are restricted. In this case, each FC has to decide which sensors are to be used by itself at each measurement time step. We propose an efficient algorithm to handle the above problem in real time. Simulation results illustrating the performance of the proposed algorithm are also presented.
KEYWORDS: Sensors, Motion models, Target detection, Data modeling, Submerged target detection, Motion measurement, Detection and tracking algorithms, Time metrology, Signal to noise ratio, Monte Carlo methods
In this paper, we assess the capability of underwater hydrophone (UH) arrays to locate and track manoeuvring targets. A UH array is a horizontal line array of omnidirectional pressure sensors that is deployed on the seabed. The measurements at each UH array are then affected by two idiosyncrasies, termed "source direction ambiguity" and "coning error". In this paper, the posterior Cramer-Rao lower bound(PCRLB) is used as the measure of system performance, providing a bound on the optimal achievable accuracy of target state estimation. We demonstrate the impact of the measurement idiosyncrasies on the PCRLB, with the bound shown to be greater (poorer performance) than when using standard bearings-only sensors. We also include clutter (i.e. we allow each measurement to be either target generated or a false positive), as well as both state-dependent measurement errors and a state-dependent probability of detection. Building on previous work, we show that the measurement origin uncertainty can again be expressed as an information reduction factor (IRF), with this IRF now shown to be a function of both the target range and orientation in relation to each UH array. We consider simulated scenarios that contain features characteristic of recent sea trials conducted by QinetiQ Ltd. The two key features of the trial scenarios is that we have very sparse prior knowledge, and each target has the potential to perform a series of manoeuvres. We use a recent PCRLB formulation for tracking manoeuvring targets that approximates the potentially multi-modal target distribution using a best-fitting Gaussian distribution. We present simulation results for multi-sensor scenarios, demonstrating that this is indeed a difficult tracking problem. Tracking is particularly difficult when the target crosses the line of the UH arrays, making triangulation difficult; and when the target is in the "end-fire" of at least one UH array. It is also difficult to detect and triangulate distant targets. Future work will investigate the tightness of the PCRLB when compared with the performance of state-of-the-art tracking algorithms.
In this paper we consider the general problem of managing an array of sensors in order to track multiple targets in the presence of measurement origin uncertainty. There are two complicating factors: the first is that because of physical limitations (e.g., communication bandwidth) only a small number of sensors can be utilized at any one time. The second complication is that the associations of measurements to targets/clutter are unknown. It
is this second factor that extends our previous work [14]. Hence sensors must be utilized in an efficient manner to alleviate association ambiguities and allow accurate target state estimation. Our sensor management technique is then based on controlling the Posterior Cramer-Rao Lower Bound (PCRLB), which provides a measure of the optimal achievable accuracy of target state estimation. Only recently have expressions for multitarget PCRLBs been determined [7], and the necessary simulation techniques are computationally expensive. However, in this paper we propose some approximations that reduce the computational load and we present two sensor selection
strategies for closely spaced (but, resolved) targets. Simulation results show the ability of the PCRLB based sensor management technique to allow efficient utilization of the sensor resources, allowing accurate target state estimation.
Multi-sensor management is concerned with utilising the available sensor resource in the most effective way possible to detect, classify or track targets. We are primarily concerned with utilising the sensor resource in order to track a target as closely as possible. Previous work in this area has focused on tracking targets whose motion is either governed by a pre-specified model, or manoeuvre at pre-specified times. In particular, targets do not adapt their behaviour in order to make tracking them more difficult. In this paper, we apply state of the art sensor management techniques to a scenario in which the target is actively trying to avoid being tracked. This creates a conflict between the aims of sensor network and the target, which these previous techniques are unable to resolve. We formulate the action (e.g. manoeuvre) of the sensor resource (the pursuer) and the target (the evader) as a two-player game. The "reward" each player receives is then dependent on the actions chosen and the ensuing tracking accuracy. We also allow multi-step planning, in which the action of each player takes into account the impact this will have on future expected rewards (i.e. future tracking performance). We show that, form the pursuer's perspective, tracking performance is significantly improved by multi-step planning. Conversely, the evader can substantially degrade tracking performance by following the strategies we recommend, when compared to either performing random manoeuvres or moving with constant velocity.
In this paper, we implement a previously developed sensor management framework within the domain of multistatic radar resource management. The methodology is based on controlling the Posterior Cram´er-Rao Lower Bound (PCRLB) which provides a bound on the performance of any unbiased target state estimator. In the second part of the paper, the additional complication of the Doppler Blind Zone, inside which the target cannot be detected, is considered. In the case of missed
detections, the PCRLB has been shown to be overly optimistic, so we use a performance measure which more accurately accounts for missed detections. However, existing measures fail to accommodate constraints arising from the blind zone, so we modify the measure to incorporate this extra information. The modified measure is shown to give a more accurate estimate of tracking performance, facilitating efficient resource management.
Recently a general framework for sensor resource management, which has been shown to allow efficient and effective utilization of a multisensor system was introduced in5. The basis of this technique is to use the Posterior Cramer-Rao Lower Bound (PCRLB) to quantify and control the optimal achievable accuracy of target state estimation. In the current paper we extend this framework by addressing the issues of imperfect sensor placement and uncertain sensor movement (e.g., sensor drift). In contrast the previous work considered only
the case where the sensor location is known exactly. The crucial consideration is then how these two forms of uncertainty affect the sensor management strategy. If unaccounted for, these uncertainties will render the output of the resource manager useless. We adjust the PCRLB to account for sensor location uncertainty, and we also allow for measurement origin uncertainty (missed target originated detections and false alarms). The work is motivated by the problem of tracking a submarine by adaptively deploying sonobuoys from a helicopter. Simulation results are presented to show the advantages of accounting for sensor location uncertainty within this focal domain of anti-submarine warfare. The same technique can be used for tracking using unattended ground sensors (UGS) or unmanned aerial vehicles (UAV).
In this paper, we build on an established framework for dynamic multi-sensor resource management. The framework is based on the control of the posterior Cramer-Rao lower bound, which provides a bound on the achievable accuracy of target state estimation. We further develop this framework to increase the utility of each sensor by deploying new sensors ahead of the target and in its path. The modified framework is demonstrated in the deployment and utilization of azimuth-only sensors in tracking a single target. Simulation results show that the enhanced strategy is able to accurately track the
target while significantly reducing the number of sensors required. However this is at a cost of a significant increase in computation time which may make the technique unsuitable for some sensor management applications.
Large-scale sensor array management has applications in a number of target tracking problems. For example, in ground target tracking, hundreds or even thousands of unattended ground sensors (UGS) may be dropped over a large surveillance area. At any one time it may then only be possible to utilize a very small number of the available sensors at the fusion center because of bandwidth limitations. A similar situation may arise in tracking sea surface or underwater targets using a large number of sonobuoys. The general problem is then to select a subset of the available sensors in order to optimize tracking performance. The Posterior Cramer-Rao Lower Bound (PCRLB), which quantifies the obtainable accuracy of target state estimation, is used as the basis for network management. In a practical scenario with even hundreds of sensors, the number of possible sensor
combinations would make it impossible to enumerate all possibilities in real-time. Efficient local (or greedy) search techniques must then be used to make the computational load manageable. In this paper we introduce an efficient search strategy for selecting a subset of the sensor array for use during each sensor change interval in multi-target tracking. Simulation results illustrating the performance of the sensor array manager are also presented.
This paper investigates how the targeting capability of a distributed data fusion system can be improved though the use of intelligent sensor management. The research reported here builds upon previous results from QinetiQ's air-to-ground fusion programme and sensor management research. QinetiQ's previously reported software test-bed for developing and evaluating data fusion algorithms has been enhanced to include intelligent sensor management functions and weapon fly-out models. In this paper details of the enhancements are provided together with a review of the sensor management algorithms employed. These include flight path optimization of airborne sensors to minimize target state estimation error, sensor activation control and sightline management of individual sensors for optimal targeting performance. Initial results from investigative studies are presented and conclusions are drawn.
This paper describes the development of a general framework for the efficient management of multiple sensors in target tracking. The basis of the technique is to quantify, and subsequently control, the accuracy of target state estimation. The Posterior Cramer-Rao lower bound provides the means of achieving this aim by enabling us to determine a bound on the performance of all unbiased estimators of the unknown target state. The general approach is then to use optimization techniques to control the measurement process in order to achieve accurate target state estimation. We are concerned primarily with the deployment and utilization of a limited sensor resource. We also allow for measurement origin uncertainty, with sensor measurements either target generated or false alarms. We exploit previous work to determine a general expression for the Fisher Information Matrix in this case. We show that by making certain assumptions we can express the measurement uncertainty as a constant information reduction factor. This enables the Fisher Information Matrix to be calculated quickly, allowing Cramer-Rao bounds to be utilized for real-time, online sensor management.
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