Optimal search in structured environments
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NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- This thesis is concerned with the development of optimal search techniques to find a target in a structured environment. It is necessary in many rescue and security applications for the responders to efficiently find and reach the phenomena of interest. Although the target location is by definition not precisely known, it is nevertheless imperative to make the best use of any available information. Given a known area described as a set of connected regions, a prior belief on the target location and a model of likely target motion, the underlying task addressed is to determine the best paths for the one or more searchers to follow to maximise their effectiveness. As the most related problem discussed in literature, the Optimal Searcher Path (OSP) problem, assumes that the searcher can instantly relocate between regions, one of the main contributions in this thesis is an extension to the OSP problem to deal with the more realistic scenario where a searcher needs a finite time to physically travel from one region to another. This work first considers the search of an indoor environment for a stationary target with the aim of minimising the expected time to detection. A dynamic programming approach is used to find an optimal ordering of regions to inspect. The proposed technique is also extended to the search for multiple targets. Secondly, for maximising the probability of detecting a moving target in a structured environment, the more general Optimal Searcher Path Problem with non-uniform Travel times (OSPT) is formulated. A key contribution is a branch and bound solution approach with a new bounding technique, the Discounted MEAN bound, which also provides much tighter bounds for the OSP problem compared to existing methods. As this improvement is gained with almost no increase in computational time, optimal search paths can thus be feasibly derived for longer time horizons. Finally, a multi-agent problem where the searchers are aided by scouts that can help find but not rescue the target is considered. Envisaged applications include firefighters (searchers) entering a building with a number of scouting robots. While the process terminates as soon as a searcher finds the target, successful scout detections can only improve on the knowledge available to guide future searches. The solution framework must therefore plan not only to maximise the probability of the searchers directly finding the target, but also put them in the best position to exploit any new information obtained from detections by scouts. It is shown that the problem can be partitioned into a series of modified OSP problems, through which the complete set of paths necessitated by each possible scout detection (and non-detection) can be obtained. Optimal and heuristic solutions to this problem are presented.
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