20 research outputs found
Sensor-driven online coverage planning for autonomous underwater vehicles
Abstract-At present, autonomous underwater vehicle (AUV) mine countermeasure (MCM) surveys are normally pre-planned by operators using ladder or zig-zag paths. Such surveys are conducted with side-looking sonar sensors whose performance is dependant on environmental, target, sensor, and AUV platform parameters. It is difficult to obtain precise knowledge of all of these parameters to be able to design optimal mission plans offline. This research represents the first known sensor driven online approach to seabed coverage for MCM. A method is presented where paths are planned using a multi-objective optimization. Information theory is combined with a new concept coined branch entropy based on a hexagonal cell decomposition. The result is a planning algorithm that not only produces shorter paths than conventional means, but is also capable of accounting for environmental factors detected in situ. Hardware-in-the-loop simulations and in water trials conducted on the IVER2 AUV show the effectiveness of the proposed method. Index Terms-autonomous underwater vehicles, coverage path planning, information gain, hardware-in-the-loop, mine countermeasure, sidescan sonar, adaptive mission plannin
Adaptive sampling in autonomous marine sensor networks
Submitted in partial fulfillment of the requirements for the degree of
Doctor of Philosophy at the Massachusetts Institute of Technology and the
Woods Hole Oceanographic Institution June 2006In this thesis, an innovative architecture for real-time adaptive and cooperative control of autonomous sensor platforms in a marine sensor network is described in the context of the autonomous oceanographic network scenario. This architecture has three major components, an intelligent, logical sensor that provides high-level environmental state information to a behavior-based autonomous vehicle control system, a new approach to behavior-based control of autonomous vehicles using multiple objective functions that allows reactive control
in complex environments with multiple constraints, and an approach to cooperative
robotics that is a hybrid between the swarm cooperation and intentional cooperation approaches.
The mobility of the sensor platforms is a key advantage of this strategy, allowing
dynamic optimization of the sensor locations with respect to the classification or localization of a process of interest including processes which can be time varying, not spatially isotropic and for which action is required in real-time.
Experimental results are presented for a 2-D target tracking application in which fully
autonomous surface craft using simulated bearing sensors acquire and track a moving target in open water. In the first example, a single sensor vehicle adaptively tracks a target while simultaneously relaying the estimated track to a second vehicle acting as a classification
platform. In the second example, two spatially distributed sensor vehicles adaptively track a moving target by fusing their sensor information to form a single target track estimate.
In both cases the goal is to adapt the platform motion to minimize the uncertainty of the target track parameter estimates. The link between the sensor platform motion and the target track estimate uncertainty is fully derived and this information is used to develop the
behaviors for the sensor platform control system. The experimental results clearly illustrate the significant processing gain that spatially distributed sensors can achieve over a single sensor when observing a dynamic phenomenon as well as the viability of behavior-based
control for dealing with uncertainty in complex situations in marine sensor networks.Supported by the Office of Naval Research, with a 3-year National Defense Science and Engineering Grant Fellowship and research
assistantships through the Generic Ocean Array Technology Sonar (GOATS) project, contract N00014-97-1-0202 and contract N00014-05-G-0106 Delivery Order 008, PLUSNET: Persistent Littoral Undersea Surveillance Network
Semantic-based adaptive mission planning for unmanned underwater vehicles
Current underwater robotic platforms rely upon waypoint-based scripted missions which
are described by the operator a-priori. This renders systems incapable of reacting to
the unexpected. In this thesis, we claim that the ability to autonomously adapt the
decision making process is the key to facilitating the change over from human intervention
to intelligent autonomy. We identify goal-based declarative mission planning
as an attractive solution to autonomous adaptability because it combines autonomous
decision making with higher levels of human interaction.
Goal-based mission planning requires the use of abstract knowledge representation
and situation awareness to link the prior knowledge provided by the operator with
the information coming from the processed sensor data. To achieve this, we propose
a semantic-based knowledge representation framework that allows this integration of
prior and processed information among all different agents available in the platform.
In order to evaluate adaptive mission planning techniques, we also introduce a novel
metric which measures the proximity between plans. We demonstrate that this metric
is better informed than previous metrics for measuring the adaptation process.
In this thesis we implement three different approaches to goal-based mission planning
in order to investigate which approach is most appropriate under different circumstances.
The first approach, continuous mission planning, focusses on long-term
deployment. This approach is based on a continuous re-assessment of the status of
the mission environment. Using our proximity metric, we evaluated this approach
and show that there is a high degree of similarity between our approach and the humanly
driven adaptation, both in a known static environment and in a partially-known
dynamic discoverable environment. The second, service-oriented mission planning,
makes use of the semantic framework to provide autonomous mission planning for
the dynamic discovery of the services published by the different agents in the system.
This allows platform independence, easing the manual creation of mission plans, and
robustness to changes. We show that this approach produces the same plans as the
baseline which was explicitly provided with the platform configuration. The last approach,
mission plan repair, handles the scenario where small changes occur in the
mission environment and there are limited resources for planning. We develop and
deploy a mission plan repair approach within a semantic-based autonomous planning
system in a real underwater vehicle. Experiments demonstrate that the integrated system
is capable of providing mission adaptation for maintaining the operability of the
host platform in the face of unexpected events
Advances in integrating autonomy with acoustic communications for intelligent networks of marine robots
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2013Autonomous marine vehicles are increasingly used in clusters for an array of oceanographic
tasks. The effectiveness of this collaboration is often limited by communications:
throughput, latency, and ease of reconfiguration. This thesis argues that improved communication
on intelligent marine robotic agents can be gained from acting on knowledge
gained by improved awareness of the physical acoustic link and higher network layers by
the AUV’s decision making software.
This thesis presents a modular acoustic networking framework, realized through a
C++ library called goby-acomms, to provide collaborating underwater vehicles with an
efficient short-range single-hop network. goby-acomms is comprised of four components
that provide: 1) losslessly compressed encoding of short messages; 2) a set of message
queues that dynamically prioritize messages based both on overall importance and time
sensitivity; 3) Time Division Multiple Access (TDMA) Medium Access Control (MAC) with
automatic discovery; and 4) an abstract acoustic modem driver.
Building on this networking framework, two approaches that use the vehicle’s “intelligence”
to improve communications are presented. The first is a “non-disruptive”
approach which is a novel technique for using state observers in conjunction with an entropy
source encoder to enable highly compressed telemetry of autonomous underwater
vehicle (AUV) position vectors. This system was analyzed on experimental data and implemented
on a fielded vehicle. Using an adaptive probability distribution in combination
with either of two state observer models, greater than 90% compression, relative to
a 32-bit integer baseline, was achieved.
The second approach is “disruptive,” as it changes the vehicle’s course to effect an improvement
in the communications channel. A hybrid data- and model-based autonomous
environmental adaptation framework is presented which allows autonomous underwater
vehicles (AUVs) with acoustic sensors to follow a path which optimizes their ability to
maintain connectivity with an acoustic contact for optimal sensing or communication.I wish to acknowledge the sponsors of this research for their generous support
of my tuition, stipend, and research: the WHOI/MIT Joint Program, the MIT Presidential Fellowship, the Office of Naval Research (ONR) # N00014-08-1-0011, # N00014-08-1-0013, and the ONR PlusNet Program Graduate Fellowship, the Defense Advanced Research Projects Agency (DARPA) (Deep Sea Operations: Applied Physical Sciences (APS) Award # APS 11-15 3352-006, APS 11-15-3352-215 ST 2.6 and 2.7
Experiments on Surface Reconstruction for Partially Submerged Marine Structures
Over the past 10 years, significant scientific effort has been dedicated to the problem of three-dimensional (3-D) surface reconstruction for structural systems. However, the critical area of marine structures remains insufficiently studied. The research presented here focuses on the problem of 3-D surface reconstruction in the marine environment. This paper summarizes our hardware, software, and experimental contributions on surface reconstruction over the past few years (2008–2011). We propose the use of off-the-shelf sensors and a robotic platform to scan marine structures both above and below the waterline, and we develop a method and software system that uses the Ball Pivoting Algorithm (BPA) and the Poisson reconstruction algorithm to reconstruct 3-D surface models of marine structures from the scanned data. We have tested our hardware and software systems extensively in Singapore waters, including operating in rough waters, where water currents are around 1–2 m/s. We present results on construction of various 3-D models of marine structures, including slowly moving structures such as floating platforms, moving boats, and stationary jetties. Furthermore, the proposed surface reconstruction algorithm makes no use of any navigation sensor such as GPS, a Doppler velocity log, or an inertial navigation system.Singapore-MIT Alliance for Research and Technology. Center for Environmental Sensing and Modelin
Cooperative algorithms for a team of autonomous underwater vehicles
Ph.DDOCTOR OF PHILOSOPH
Cooperative localization for autonomous underwater vehicles
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2009Self-localization of an underwater vehicle is particularly challenging due to the absence
of Global Positioning System (GPS) reception or features at known positions
that could otherwise have been used for position computation. Thus Autonomous
Underwater Vehicle (AUV) applications typically require the pre-deployment of a set
of beacons.
This thesis examines the scenario in which the members of a group of AUVs
exchange navigation information with one another so as to improve their individual
position estimates.
We describe how the underwater environment poses unique challenges to vehicle
navigation not encountered in other environments in which robots operate and how
cooperation can improve the performance of self-localization. As intra-vehicle communication
is crucial to cooperation, we also address the constraints of the communication
channel and the effect that these constraints have on the design of cooperation
strategies.
The classical approaches to underwater self-localization of a single vehicle, as
well as more recently developed techniques are presented. We then examine how
methods used for cooperating land-vehicles can be transferred to the underwater
domain. An algorithm for distributed self-localization, which is designed to take the
specific characteristics of the environment into account, is proposed.
We also address how correlated position estimates of cooperating vehicles can lead
to overconfidence in individual position estimates.
Finally, key to any successful cooperative navigation strategy is the incorporation
of the relative positioning between vehicles. The performance of localization
algorithms with different geometries is analyzed and a distributed algorithm for the
dynamic positioning of vehicles, which serve as dedicated navigation beacons for a
fleet of AUVs, is proposed.This work was funded by Office of Naval Research grants N00014-97-1-0202,
N00014-05-1-0255, N00014-02-C-0210, N00014-07-1-1102 and the ASAP MURI
program led by Naomi Leonard of Princeton University