Author name cluster

Franz S. Hover

Possible papers associated with this exact author name in Arrow. This page groups case-insensitive exact name matches and is not a full identity disambiguation profile.

22 papers

1 author row

IROS Conference 2018 Conference Paper

Multibeam Data Processing for Underwater Mapping

Pedro Vaz Teixeira
Franz S. Hover
John J. Leonard
Michael Kaess

From archaeology to the inspection of subsea structures, underwater mapping has become critical to many applications. Because of the balanced trade-off between range and resolution, multibeam sonars are often used as the primary sensor in underwater mapping platforms. These sonars output an image representing the intensity of the received acoustic echos over space, which must be classified into free and occupied regions before range measurements are determined and spatially registered. Most classifiers found in the underwater mapping literature use local thresholding techniques, which are highly sensitive to noise, outliers, and sonar artifacts typically found in these images. In this paper we present an overview of some of the techniques developed in the scope of our work on sonar-based underwater mapping, with the aim of improving map accuracy through better segmentation performance. We also provide experimental results using data collected with a DIDSON imaging sonar that show that these techniques improve both segmentation accuracy and robustness to outliers.

IROS Conference 2016 Conference Paper

Underwater inspection using sonar-based volumetric submaps

Pedro Vaz Teixeira
Michael Kaess
Franz S. Hover
John J. Leonard

We propose a submap-based technique for mapping of underwater structures with complex geometries. Our approach relies on the use of probabilistic volumetric techniques to create submaps from multibeam sonar scans, as these offer increased outlier robustness. Special attention is paid to the problem of denoising/enhancing sonar data. Pairwise submap alignment constraints are used in a factor graph framework to correct for navigation drift and improve map accuracy. We provide experimental results obtained from the inspection of the running gear and bulbous bow of a 600-foot, Wright-class supply ship.

IROS Conference 2015 Conference Paper

Decentralized multi-vehicle dynamic pursuit using acoustic TDOA measurements

Mei Yi Cheung
Joshua Leighton
Franz S. Hover

Multi-vehicle operations in the ocean are increasingly attractive as more vehicles become commercially available, however acoustics still defines the main practical channel for long-range wireless communication underwater. Long transmission times, scheduling delays and packet losses remain obstacles to implementing real-time multi-vehicle cooperative control for marine vehicles. We present a control system for dynamic pursuit with multiple vehicles exchanging time-difference-of-arrival (TDOA) measurements via underwater acoustic communications. Using data from field experiments conducted with autonomous surface vehicles, we show that a decentralized controller can track fast-moving targets and formation changes, leveraging partial information updates and decreased effective cycle times. As a comparison, we show results for trials conducted with one similar but centralized control scheme.

ICRA Conference 2014 Conference Paper

Collaborative bathymetry-based localization of a team of autonomous underwater vehicles

Tan Yew Teck
Mandar A. Chitre
Franz S. Hover

Without access to GPS and high-quality visual landmarks, many autonomous underwater vehicles (AUV) face a fundamental navigation vs. cost tradeoff: advanced navigation systems that might include an INS, Doppler velocity, or long-baseline acoustics are expensive. Supporting low-cost operations, this work focuses on collaborative positioning for a team of AUV's, given a bathymetric terrain map, and only an altimeter and acoustic modem on each vehicle. The joint localization is performed via decentralized particle filtering, where we extend the usual measurement model to allow received information to modulate the importance function. We investigate the impact on performance of sensor noise, communication interval and number of vehicles. Results are shown for bathymetry maps near St. John's Island, Singapore, and for the Charles River Basin, Boston. In the second case, we ran our algorithm with physical measurements from actual vehicles executing trajectories.

IROS Conference 2013 Conference Paper

Autonomous mobile acoustic relay positioning as a multi-armed bandit with switching costs

Mei Yi Cheung
Joshua Leighton
Franz S. Hover

Underwater acoustic communication channels display highly variable and stochastic performance, especially in multipath-limited shallow-water and harbor environments. A mobile acoustic node can, however, learn the channel's properties as it moves about. Maximizing the cumulative data transmission through adaptive node positioning is a clean exploitation vs. exploration scenario because learning about poorly characterized locations must be balanced against exploiting known ones. While this problem is well described with the stochastic multi-armed bandit formalism, the classical assumption of costless switching is untenable in the field, where slow-moving vehicles often cover large distances. We present a heuristic adaptation to the MAB Gittins index rule with limited policy enumeration to account for switching costs, and describe field experiments conducted in the Charles River (Boston MA). The field data establish that the MAB and its switching cost extension are tractable in this application, and that performance is consistently superior to that of ϵ-greedy policies.

ICRA Conference 2013 Conference Paper

Experiments in dynamic control of autonomous marine vehicles using acoustic modems

Eric Gilbertson
Brooks L. Reed
Joshua Leighton
Mei Yi Cheung
Franz S. Hover

Marine robots are an increasingly attractive means for observing and monitoring in the ocean, but underwater acoustic communication (“acomms”) remains a major challenge, especially for real-time control. Packet loss occurs widely, bit rates are low, and there are significant delays. We consider here strategies for feedback control with acomms links in either the sensor-controller channel, or the controller-actuator channel. On the controller-actuator side we implement sparse packetized predictive control (S-PPC), which simultaneously addresses packet-loss and the data rate limit. For the sensor-controller channel we study a modified information filter (MIF) in a Linear Quadratic Gaussian (LQG) control scheme. Field experiments were carried out with both approaches, regulating crosstrack error in a robotic kayak using acomms. Outcomes with both the S-PPC and MIF LQG confirm that good performance is achievable.

ICRA Conference 2013 Conference Paper

Multi-armed bandit formulation for autonomous mobile acoustic relay adaptive positioning

Mei Yi Cheung
Joshua Leighton
Franz S. Hover

We apply the stationary multi-armed bandit (MAB) formalism to the problem of maximizing underwater acoustic data transmission through adaptive positioning of a mobile relay. Shallow-water environments, in particular, show complex and variable performance across physical space. This is a classic exploration vs. exploitation scenario, since choosing to visit new sites to learn their properties may be disadvantageous for cumulative data transmission if a better-performing site is already known with high confidence. Normal Gittins indices define a rule by which an optimal relay position can be chosen at each decision epoch, without assuming prior information and while pursuing the overall goal of maximizing total data transmission. We present results from shallow-water field experiments conducted with autonomous surface vehicles and acoustic modems transmitting data through a one-way, two-hop network in the Charles River Basin, Boston.

IROS Conference 2013 Conference Paper

Tracking ocean fronts with multiple vehicles and mixed communication losses

Brooks L. Reed
Franz S. Hover

We make two contributions toward integrated monitoring over large spatial scales, with multiple collaborating vehicles. Our focus is dynamic ocean features such as fronts and plumes. To support strong networked-control designs, we first develop a clean linear time-invariant framework for tracking features, that directly couples the global structure of the process to vehicle positioning. To address the packet loss inherent in underwater acoustic communications, we then extend the synthesis technique of Imer et al. [1] to the case where measurements and control commands suffer loss with differing statistics among the multiple channels. Simulations show that the integrated feedback system achieves good performance in front tracking.

ICAPS Conference 2012 Conference Paper

Sampling-Based Coverage Path Planning for Inspection of Complex Structures

Brendan J. Englot
Franz S. Hover

We present several new contributions in sampling-based coverage path planning, the task of finding feasible paths that give 100% sensor coverage of complex structures in obstaclefilled and visually occluded environments. First, we establish a framework for analyzing the probabilistic completeness of a sampling-based coverage algorithm, and derive results on the completeness and convergence of existing algorithms. Second, we introduce a new algorithm for the iterative improvement of a feasible coverage path; this relies on a samplingbased subroutine that makes asymptotically optimal local improvements to a feasible coverage path based on a strong generalization of the RRT* algorithm. We then apply the algorithm to the real-world task of autonomous in-water ship hull inspection. We use our improvement algorithm in conjunction with redundant roadmap coverage planning algorithm to produce paths that cover complex 3D environments with unprecedented efficiency.

IROS Conference 2012 Conference Paper

Sampling-based sweep planning to exploit local planarity in the inspection of complex 3D structures

Brendan J. Englot
Franz S. Hover

We present a hybrid algorithm that plans feasible paths for 100% sensor coverage of complex 3D structures. The structures to be inspected are segmented to isolate planar areas, and back-and-forth sweep paths are generated to view as much of these planar areas as possible while avoiding collision. A randomized planning procedure fills in the remaining gaps in coverage. The problem of selecting an order to traverse the elements of the inspection is solved by reduction to the traveling salesman problem. We present results of the planning algorithm for an autonomous underwater vehicle inspecting the in-water portion of a ship hull. The randomized configurations succeed in observing confined and occluded areas, while the 2D sweep paths succeed in covering the open areas.

ICRA Conference 2012 Conference Paper

Uncertainty-driven view planning for underwater inspection

Geoffrey A. Hollinger
Brendan J. Englot
Franz S. Hover
Urbashi Mitra
Gaurav S. Sukhatme

We discuss the problem of inspecting an underwater structure, such as a submerged ship hull, with an autonomous underwater vehicle (AUV). In such scenarios, the goal is to construct an accurate 3D model of the structure and to detect any anomalies (e. g. , foreign objects or deformations). We propose a method for constructing 3D meshes from sonar-derived point clouds that provides watertight surfaces, and we introduce uncertainty modeling through non-parametric Bayesian regression. Uncertainty modeling provides novel cost functions for planning the path of the AUV to minimize a metric of inspection performance. We draw connections between the resulting cost functions and submodular optimization, which provides insight into the formal properties of active perception problems. In addition, we present experimental trials that utilize profiling sonar data from ship hull inspection.

ICRA Conference 2011 Conference Paper

Mission design for compressive sensing with mobile robots

Robert Hummel
Sameera Poduri
Franz S. Hover
Urbashi Mitra
Gaurav S. Sukhatme

This paper considers mission design strategies for mobile robots whose task is to perform spatial sampling of a static environmental field, in the framework of compressive sensing. According to this theory, we can reconstruct compressible fields using O(log n) nonadaptive measurements (where n is the number of sites of the spatial domain), in a basis that is "in coherent" to the representation basis [1]; random uncorrelated measurements satisfy this incoherence requirement. Because an autonomous vehicle is kinematically constrained and has finite energy and communication resources, it is an open question how to best design missions for CS reconstruction. We compare a two-dimensional random walk, a TSP approximation to pass through random points, and a randomized boustrophedon (lawnmower) strategy. Not unexpectedly, all three approaches can yield comparable reconstruction performance if the planning horizons are long enough; if planning occurs only over short time scales, the random walk will have an advantage.

ICRA Conference 2011 Conference Paper

Multi-goal feasible path planning using ant colony optimization

Brendan J. Englot
Franz S. Hover

A new algorithm for solving multi-goal planning problems in the presence of obstacles is introduced. We extend ant colony optimization (ACO) from its well-known application, the traveling salesman problem (TSP), to that of multi-goal feasible path planning for inspection and surveillance applications. Specifically, the ant colony framework is combined with a sampling-based point-to-point planning algorithm; this is compared with two successful sampling-based multi-goal planning algorithms in an obstacle-filled two-dimensional environment. Total mission time, a function of computational cost and the duration of the planned mission, is used as a basis for comparison. In our application of interest, autonomous underwater inspections, the ACO algorithm is found to be the best-equipped for planning in minimum mission time, offering an interior point in the tradeoff between computational complexity and optimality.

ICRA Conference 2011 Conference Paper

Vertical glider robots for subsea equipment delivery

Brooks L. Reed
Charles Ambler
Julio Guerrero
Franz S. Hover

We have developed an underwater vehicle that offers significant performance improvements over existing sub sea elevators. Our Vertical Glider Robot falls under its own weight to a precise location on the seafloor, employing streamlining, active steering, and basic navigation instrumentation. We examine typical at-sea mission requirements, mention several key governing parameters, and outline our design approach. We then describe a prototype device, and present results from model-scale experiments.

IROS Conference 2010 Conference Paper

Imaging sonar-aided navigation for autonomous underwater harbor surveillance

Hordur Johannsson
Michael Kaess
Brendan J. Englot
Franz S. Hover
John J. Leonard

In this paper we address the problem of drift-free navigation for underwater vehicles performing harbor surveillance and ship hull inspection. Maintaining accurate localization for the duration of a mission is important for a variety of tasks, such as planning the vehicle trajectory and ensuring coverage of the area to be inspected. Our approach only uses onboard sensors in a simultaneous localization and mapping setting and removes the need for any external infrastructure like acoustic beacons. We extract dense features from a forward-looking imaging sonar and apply pair-wise registration between sonar frames. The registrations are combined with onboard velocity, attitude and acceleration sensors to obtain an improved estimate of the vehicle trajectory. We show results from several experiments that demonstrate drift-free navigation in various underwater environments.

IROS Conference 2010 Conference Paper

Inspection planning for sensor coverage of 3D marine structures

Brendan J. Englot
Franz S. Hover

We introduce an algorithm to achieve complete sensor coverage of complex, three-dimensional structures surveyed by an autonomous agent with multiple degrees of freedom. Motivated by the application of an ocean vehicle performing an autonomous ship hull inspection, we consider a planning problem for a fully-actuated, six degree-of-freedom hovering AUV using a bathymetry sonar to inspect the complex structures underneath a ship hull. We consider a discrete model of the structure to be inspected, requiring only that the model be provided in the form of a closed triangular mesh. A dense graph of feasible paths is constructed in the robot's configuration space until the set of edges in the graph allows complete coverage of the structure. Then, we approximate the minimum-cost closed walk along the graph which observes 100% of the structure. We emphasize the embedding of observations within the edges of the graph as a means of utilizing all available sensor data in planning the inspection.

ICRA Conference 2009 Conference Paper

Analytic error variance predictions for planar vehicles

Matthew Greytak
Franz S. Hover

Path planning algorithms that incorporate risk and uncertainty need to be able to predict the evolution of path-following error statistics for each candidate plan. We present an analytic method to predict the evolving error statistics of a holonomic vehicle following a reference trajectory in a planar environment. This method is faster than integrating the plant through time or performing a Monte Carlo simulation. It can be applied to systems with external Gaussian disturbances, and it can be extended to handle plant uncertainty through numerical quadrature techniques.

IROS Conference 2009 Conference Paper

Path planning for data assimilation in mobile environmental monitoring systems

Franz S. Hover

By combining a low-order model of forecast errors, the extended Kalman filter, and classical continuous optimization, we develop an integrated methodology for planning mobile sensor paths to sample continuous fields. Agent trajectories are developed that specifically take into account the fact that data collected will be used for near real-time assimilation with large predictive models. This aspect of the problem has significant implications because the trajectories generated are very different from those which do not take the assimilation step into account, and their performance in controlling error is notably better.

IROS Conference 2009 Conference Paper

Stability and robustness analysis tools for marine robot localization and SLAM applications

Brendan J. Englot
Franz S. Hover

Our aim is to explore the fundamental stability issues of a robotic vehicle carrying out localization, mapping, and feedback control in a perturbation-filled environment. Motivated by the application of an ocean vehicle performing an autonomous ship hull inspection, our planar vehicle model performs localization using point features from a given map. Cases in which the agent must update the map are also considered. The stability of the controller and estimator duo is investigated using a pair of theorems requiring boundedness and convergence of the transition matrix Euclidean norm. These theorems yield a stability test for the feedback controller. Perturbations are then considered using a theorem on the convergence on the perturbed system transition matrix, yielding a robustness test for the estimator. Together, these tests form a set of tools which can be used in planning and evaluating the robustness of marine vehicle survey trajectories, which is demonstrated through experiment.

ICRA Conference 2008 Conference Paper

SLAM for ship hull inspection using exactly sparse extended information filters

Matthew R. Walter
Franz S. Hover
John J. Leonard

Many important missions for autonomous underwater vehicles (AUVs), such as undersea inspection of ship hulls, require integrated navigation, control, and motion planning in complex, 3D environments. This paper describes a SLAM implementation using forward-looking sonar (FLS) data from a highly maneuverable, hovering AUV performing a ship hull inspection mission. The exactly sparse extended information filter (ESEIF) algorithm is applied to perform SLAM based upon features manually selected within FLS images. The results demonstrate the ability to effectively map a ship hull in a challenging marine environment. This provides a foundation for future work in which real-time SLAM will be integrated with motion planning and control to achieve autonomous coverage of a complete ship hull.

ICRA Conference 2008 Conference Paper

Stability of double-integrator plants controlled using real-time SLAM maps

Franz S. Hover

The position control of agents having double-integrator dynamic response, with explicit dependence on an estimator that simultaneously reconstructs agent states and refines a feature map, is considered. We show that under broad conditions the phase and gain margins of an equivalent control system based on absolute navigation sensors can be significantly eroded when the dynamic map is used. The closed-loop bandwidth achieved depends strongly on the bandwidth of the filter, which is in turn dictated by the ratio of process to sensor noise, on the control gains, and on the arrangement of features being tracked. The findings are relevant to the integration of SLAM algorithms in high-performance positioning of mobile agents. A specific example is the case undersea robots working near large structures, where traditional navigation systems may not be practical.

IROS Conference 2008 Conference Paper

Underactuated point stabilization using predictive models with application to marine vehicles

Matthew Greytak
Franz S. Hover

Point stabilization of an underactuated vehicle is most often accomplished using a periodic time-varying control law, resulting in oscillatory trajectories. We present a two-stage algorithm that achieves point stabilization without oscillatory behavior. A low-level controller regulates as many outputs as available control inputs. The unregulated states are generally nonzero when the regulated states have converged, but for certain initial conditions the vehicle arrives at the origin of the state space using only the low-level controller. This set of initial conditions forms a manifold in the state space. A separate Lyapunov-based manifold convergence controller drives the vehicle states to this manifold so that the low-level controller can bring the vehicle to the origin. We provide experimental results of this two-stage algorithm applied to a 1. 25-meter ship model.