742 research outputs found
Non-myopic Sensor Path Planning for Emitter Localization with a UAV
This paper addresses the problem of localizing a stationary RF emitter with a mobile UAV, equipped with a single directional antenna. By rotating around its vertical axis, it determines a bearing towards the emitter. Our interest is in optimally selecting the measurement positions to achieve a fast localization. The majority of such systems described in the literature use greedy planning to select the next measurement position. This work experimentally tests an algorithm that performs a non-myopic planning until the final localization step. The algorithm is based on the policy rollout principle and showed good performance in previous simulative studies. It is adapted to match the needs of a real world setup and evaluated in flight trials. Adaptions include the avoidance of close range measurements to prevent inaccurate measurements at high elevation, and the filtering of poor measurements
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Automatic triangulation positioning system for wide area coverage from a fixed sensors network
This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonIn a wide area that many Transmitters (TRs) operate, systems of Fixed Sensors (FS) might be used in order to detect them and find TRs position. The detection and the accurate location of a new TR entering in the area frequently can be missed if the system fails to triangulate accurately the relative readings and analyze the changes in the received data. Additionally, there are cases that a Triangulation Station Network (TSN) can detect the heading as well as the transmitter’s position wrong. This thesis presents the design of a Sensors Network (FSN) system which is able to interact with a user, and exploit the relative data of the Sensors (SRs) in real time. The system performs localization with triangulation and the SRs are detect only TRs bearing data (range free). System design and algorithms are also explained. Efficient algorithms were elaborated and the outcomes of their implementation were calculated. The system design targets to reduce system errors and increase the accuracy and the speed of detection. Synchronously and through interaction with the user and changes of relative settings and parameters will be able to offer the user accurate results on localization of TRs in the area minimizing false readings and False Triangulations (FTRNs). The system also enables the user to apply optimization techniques in order to increase the system detection rate and performance and keep the surveillance in the Field of Interest (FoI) on a high level. The optimization methodology applied for the system proves that the FSN system is able to operate with a high performance even when saturation phenomena appear. The unique outcome of the research conducted, is that this thesis paves the way to enhance the localization via Triangulation for a network of Fixed Sensors with known position. The value of this thesis is that the FSN system performs bearing only detection (Range free) with a certain accuracy and the Area of Interest (AOI) is covered efficiently
Robust Exploration Strategies for a Robot exploring a Wireless Network
Integration of robots into wireless networks is important for a number of scenarios. One of the tasks is network exploration for which the most basic case is finding the physical outline of the network. We propose a robust algorithm for exploring the outline of a network with a mobile robot. For this algorithm we study robustness against noise for several sensory inputs
Sensor Path Planning for Emitter Localization
The localization of a radio frequency (RF) emitter is relevant in many military and civilian applications. The recent decade has seen a rapid progress in the development of small and mobile unmanned aerial vehicles (UAVs), which offer a way to perform emitter localization autonomously. The path a UAV travels influences the localization significantly, making path planning an important part of a mobile emitter localization system.
The topic of this thesis is path planning for a UAV that uses bearing measurements to localize a stationary emitter. Using a directional antenna, the direction towards the target can be determined by the UAV rotating around its own vertical axis. During this rotation the UAV is required to remain at the same position, which induces a trade-off between movement and measurement that influences the optimal trajectories.
This thesis derives a novel path planning algorithm for localizing an emitter with a UAV. It improves the current state of the art by providing a localization with defined accuracy in a shorter amount of time compared to other algorithms in simulations. The algorithm uses the policy rollout principle to perform a nonmyopic planning and to incorporate the uncertainty of the estimation process into its decision. The concept of an action selection algorithm for policy rollout is introduced, which allows the use of existing optimization algorithms to effectively search the action space. Multiple action selection algorithms are compared to optimize the speed of the path planning algorithm. Similarly, to reduce computational demand, an adaptive grid-based localizer has been developed.
To evaluate the algorithm an experimental system has been built and the algorithm was tested on this system. Based on initial experiments, the path planning algorithm has been modified, including a minimal distance to the emitter and an outlier detection step. The resulting algorithm shows promising results in experimental flights
The significance of passive acoustic array-configurations on sperm whale range estimation when using the hyperbolic algorithm
In cetacean monitoring for population estimation, behavioural studies or mitigation,
traditional visual observations are being augmented by the use of Passive Acoustic
Monitoring (PAM) techniques that use the creature’s vocalisations for localisation.
The design of hydrophone configurations is evaluated for sperm whale (Physeter
macrocephalus) range estimation to meet the requirements of the current mitigation
regulations for a safety zone and behaviour research.
This thesis uses the Time Difference of Arrival (TDOA) of cetacean vocalisations with a
three-dimensional hyperbolic localisation algorithm. A MATLAB simulator has been
developed to model array-configurations and to assess their performance in source
range estimation for both homogeneous and non-homogeneous sound speed profiles
(SSP). The non-homogeneous medium is modelled on a Bellhop ray trace model, using
data collected from the Gulf of Mexico. The sperm whale clicks are chosen as an
exemplar of a distinctive underwater sound.
The simulator is tested with a separate synthetic source generator which produced a set
of TDOAs from a known source location. The performance in source range estimation
for Square, Trapezium, Triangular, Shifted-pair and Y-shape geometries is tested. The
Y-shape geometry, with four elements and aperture-length of 120m, is the most
accurate, giving an error of ±10m over slant ranges of 500m in a homogeneous medium,
and 300m in a non-homogeneous medium. However, for towed array deployments, the
Y-shape array is sensitive to angle-positioning-error when the geometry is seriously
distorted. The Shifted-pair geometry overcomes these limits, performing an initial
accuracy of ±30m when the vessel either moves in a straight line or turns to port or
starboard. It constitutes a recommendable array-configuration for towed array
deployments.
The thesis demonstrates that the number of receivers, the array-geometry and the arrayaperture
are important parameters to consider when designing and deploying a
hydrophone array. It is shown that certain array-configurations can significantly
improve the accuracy of source range estimation. Recommendations are made
concerning preferred array-configurations for use with PAM systems
The four key challenges of advanced multisensor navigation and positioning
The next generation of navigation and positioning
systems must provide greater accuracy and reliability in a range
of challenging environments to meet the needs of a variety of
mission-critical applications. No single navigation technology is
robust enough to meet these requirements on its own, so a
multisensor solution is required. Although many new navigation
and positioning methods have been developed in recent years,
little has been done to bring them together into a robust, reliable,
and cost-effective integrated system. To achieve this, four key
challenges must be met: complexity, context, ambiguity, and
environmental data handling. This paper addresses each of these
challenges. It describes the problems, discusses possible
approaches, and proposes a program of research and
standardization activities to solve them. The discussion is
illustrated with results from research into urban GNSS
positioning, GNSS shadow matching, environmental feature
matching, and context detection
Reducing Uncertainty in Head and Neck Radiotherapy with Plastic Robotics
One of the greatest challenges in achieving accurate positioning in head and neck radiotherapy is that the anatomy at and above the cervical spine does not act as a single, mechanically rigid body. Current immobilization techniques contain residual uncertainties that are especially present in the lower neck that cannot be reduced by setting up to any single landmark. The work presented describes the development of a radiotherapy friendly mostly-plastic 6D robotic platform for positioning independent landmarks, (i.e., allowing remote, independent positioning of the skull relative to landmarks in the thorax), including analysis of kinematics, stress, radiographic compatibility, trajectory planning, physical construction, and phantom measurements of correction accuracy. No major component of the system within the field of imaging or treatment had a measured attenuation value greater than 250 HU, showing compatibility with x-ray-based imaging techniques. Relative to arbitrary overall setup errors of the head (min = 1.1 mm, max = 5.2 mm vector error) the robotic platform corrected the position down to a residual overall error of 0.75 mm +/- 0.33 mm over 15 cases as measured with optical tracking. This device shows the potential for providing reductions to dose margins in head and neck therapy cases, while also reducing setup time and effort
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