Technical session talks from ICRA 2012
TechTalks from event: Technical session talks from ICRA 2012
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Marine Robotics II
Opportunistic Localization of Underwater Robots Using Drifters and BoatsThe paper characterizes the localization performance of an Autonomous Underwater Vehicle (AUV) when it moves in environments where floating drifters or surface vessels are present and can be used for relative localization. In particular, we study how localization performance is affected by parameters e.g. AUV mobility, surface objects density, the available measurements (ranging and/or bearing) and their visibility range. We refer to known techniques for estimation performance evaluation and probabilistic mobility models, and we bring them together to provide a solid numerical analysis for the considered problem. We perform an extensive simulations in different scenarios, and, as a proof of concept, we show how an AUV, equipped with an upward looking sonar, can improve its localization estimate by detecting a surface vessel.
Tracking of a Tagged Leopard Shark with an AUV: Sensor Calibration and State EstimationPresented is a method for estimating the 2D planar position, velocity, and orientation states of a tagged shark. The method is designed for implementation on an Autonomous Underwater Vehicle (AUV) equipped with a stereo-hydrophone and receiver system that detects acoustic signals transmitted by a tag. The particular hydrophone system used here provides a measurement of relative bearing angle to the tag, but does not provide the sign (+ or -) of the bearing angle. A Particle Filter was used for fusing these measurements over time to produce a state estimate of the tag location. The Particle Filter combined with an active control system allowed the system to overcome the ambiguity in the sign of the bearing angle. This state estimator was validated by tracking both a stationary tag and moving tag with known positions. These experiments revealed state estimate errors were on par with those obtained by manually driven boat based tracking systems, the current method used for tracking fish and sharks over long distances. Final experiments involved the catching, releasing, and an autonomous AUV tracking of a 1 meter Leopard Shark (<i>Triakis semifasciata<i>) in SeaPlane Lagoon, Los Angeles, California.
An Experimental Momentum-Based Front Detection Method for Autonomous Underwater VehiclesFronts have been recognized as hotspots of intense biological activity. They are therefore important targets for observation to understand coastal ecology and transport in a changing ocean. With high spatial and tem- poral variability, detection and event response for frontal zones is challenging. Robotic platforms like autonomous underwater vehicles (AUVs) have shown their versatility in using automated approaches to detect a range of features; directing them using in-situ and on-shore capabilities for front detection then becomes an important tool for observ- ing such rapid and episodic changes. We introduce a novel momentum-based front detection (MBFD) algorithm de- signed to automatically detect frontal zones. MBFD utilizes a Kalman filter and a momentum accumulator function to identify significant temperature gradients associated with upwelling fronts. MBFD is designed to work at a number of levels including onboard an autonomous underwater vehicle (AUV); on-shore with a sparse, real-time data stream and post-experiment on a hi-resolution data set gathered by a robot. Such a multi-layered approach plays an important role in mixed human-computer decision making for oceanographers making coordinating sampling and asset allocation strategies in large multi-robot field experiments in the coastal ocean.
An Evaluation of Sampling Path Strategies for an Autonomous Underwater VehicleA critical problem in planning sampling paths for autonomous underwater vehicles is balancing obtaining an accurate scalar field estimation against efficiently utilizing the stored energy capacity of the sampling vehicle. Adaptive sampling approaches can only provide solutions when real-time and a priori environmental data is available. Through utilizing a cost-evaluation function to experimentally evaluate various sampling path strategies for a wide range of scalar fields and sampling densities, it is found that a systematic spiral sampling path strategy is optimal for high-variance scalar fields for all sampling densities and low-variance scalar fields when sampling is sparse. The random spiral sampling path strategy is found to be optimal for low-variance scalar fields when sampling is dense.
Field Performance Evaluation of New Methods for In-Situ Calibration of Attitude and Doppler Sensors for Underwater Vehicle NavigationWe report a comparative performance evaluation, using at-sea field data, of recently reported methods for the problem of in-situ calibration of the alignment rotation matrix between Doppler sonar velocity sensors and inertial navigation sensors arising in the navigation of underwater vehicles. Most previously reported solutions to this alignment calibration problem require the use of absolute navigation fixes of the underwater vehicle, thus requiring additional navigation sensors and/or beacons to be located externally and apart from the underwater vehicle. We briefly review four recently reported alignment calibration methods employing only internal vehicle navigation sensors for velocity, acceleration, attitude, and depth. We report the results of comparative analysis of the performance of these recently reported methods and a previously reported method with navigation data from deep-water survey missions of the Sentry autonomous underwater vehicle conducted in March, 2011 in the Kermadec Arc in the Southern Pacific Ocean. The results reveal consistent differences in performance of the various methods when analyzed on navigation data from several different vehicle dives.
A Bio-Inspired Compliant Robotic Fish: Design and ExperimentsThis paper studies the modelling, design and fabrication of a bio-inspired fish-like robot propelled by a compliant body. The key to the design is the use of a single motor to actuate the compliant body and to generate thrust. The robot has the same geometrical properties of a subcarangiform swimmer with the same length. The design is based on rigid head and fin linked together with a compliant body. The flexible part is modelled as a non-uniform cantilever beam actuated by a concentrated moment. The dynamics of the compliant body are studied and a relationship between the applied moment and the resulting motion is derived. A prototype that implements the proposed approach is built. Experiments on the prototype are done to identify the model parameters and to validate the theoretical modelling.