Thomas Glotzbach

Cooperative line of sight target tracking for heterogeneous unmanned marine vehicle teams

In this paper we present the principle of Cooperative Line Of Sight Target Tracking (CLOSTT) for Heterogeneous Unmanned Marine Vehicle Teams. Thereby CLOSTT is part of a control architecture developed to coordinate existing single heterogeneous autonomous marine vehicles as a team. Within this control architecture CLOSTT separately offers a solution to the task of following a moving underwater target with a team of unmanned marine vehicles. We describe an algorithm for target tracking by a team of autonomous marine vehicles.A general control architecture for such a team is described.Focus is put on tracking an underwater target by a team of autonomous marine vehicles.The tracking algorithm was validated in real sea trials.In the trials, an acoustic communication link was in the loop.

An Underwater Acoustic Localisation System for Assisted Human Diving Operations

Abstract In this paper we present a solution to the problem of estimating the position and orientation of a moving underwater object using acoustic range measurements relative to moving surface objects that have access to a global navigation system. We start with the description of a standard GPS Intelligent Buoy system (GIB) that employs an Extended Kalman Filter (EKF); then we adapt this principle for the concrete task of tracking a human diver utilizing moving autonomous surface crafts. To this effect, we will introduce an advanced measurement system that improves significantly the estimation quality especially in the described scenario. The paper concludes with a short description of the first sea trials of the new developed system.

Optimal Sensor Placement for Acoustic Range-Based Underwater Robot Positioning

Abstract This paper addresses the problem of optimal sensor placement for acoustic range-based underwater target positioning. In particular, we focus on the experimental set-up whereby target positioning is performed by measuring the ranges between the underwater target and a number of surface units equipped with acoustic ranging devices and GPS. With the objective of affording the reader a concise overview of the main theoretical challenges involved, this paper starts with a survey of previous work done in the area, including that of the authors. By casting the problem at hand in the form of a classical estimation problem we describe and solve the equivalent mathematical problem of maximizing the determinant of a conveniently defined Fisher Information Matrix (FIM). The latter is related to the Cramer-Rao Bound, which equals the smallest possible position estimation error variance that can possibly be achieved with any unbiased estimator. To further clarify the presentation, the details of Monte Carlo simulations in 2D and 3D with a selected target positioning algorithm are included to confirm the theoretical results numerically.

Kalman filter based team navigation for Multiple Unmanned Marine Vehicles

In applications employing multiple unmanned marine vehicles (MUMVs), the navigation has a very great importance to guarantee formation preservation and collision avoidance. While single vehicles usually base their navigation on absolute measurements (GPS, inertial navigation) to determine their position relative to the world, it may be reasonable to perform a relative navigation within vehicle teams. In this paper, we propose relative team navigation based on Kalman Filters to enable a velocity controller to establish a close formation under the typical marine constraints (narrow band width communication with low reliability). We will simulate a team of three marine vehicles and compare the results of different strategies for team navigation.

Cooperative Navigation in a Team of Marine Robots for a Specific Ocean Mapping Mission

Abstract The estimation of position and orientation of underwater agents is the basis for control, guidance and mapping tasks. We present a solution for a team of submerged marine agents for a specific scenario. The concept takes advantage of the distribution of the single agents, with one of them at the surface to access GPS measurements. The submerged units use data from a USBL unit, local sensors, and acoustic communication and employ a set of filters to perform relative navigation. We will describe the concept and show results of HIL simulation as precondition for upcoming sea trials.

Adaptive autonomy: a suggestion for the definition of the notation 'autonomy' in mobile robotics

Autonomy is a very important topic in the current research on mobile robotics (R. Arkin, 2001). Meanwhile, there is not only interest in the autonomy of a single robot, but also in the autonomy of robot swarms. Experiences made at Ilmenau Technical University during several robotic projects (T. Pfutzenreuter, 2003), (M. Eichhorn, 2004), (T. Glotzbach, 2003) showed that a problem arises concerning the meaning of autonomy. Since there is no clear definition about what a robot has to achieve to be called autonomous, this term is used in very different situations. This paper gives an overview of the different aspects of autonomy of robots and robot swarms. Adapted from experiments accomplished in simulation, a suggestion is made for a possible definition of the term autonomy that can be used as a basis for discussions.

Advanced Trajectory Planning for Obstacle Avoidance of Multiple Unmanned Marine Vehicles (MUMVs)

Abstract In this paper we present our work and results in the framework of obstacle avoiding for marine vehicle teams by means of trajectory planning. Based on a team of maritime systems, such as Autonomous Underwater Vehicles (AUVs) or Autonomous Surface Vehicles (ASVs), which are intended to perform a preplanned mission in a given formation topology, methods for trajectory planning are investigated which guarantee for both obstacle-free paths and formation preservation. The proposed solution contains advanced graph search and trajectory smoothing to generate executable path for the vehicles.

Relative positioning of multiple underwater vehicles in the GREX project

Abstract This paper discusses the estimation of relative positions of a swarm of autonomous underwater or surface vehicles. The solution of this problem is crucial for performing a coordinated path following in a spatial formation. It forms a necessary prerequisite for establishing a coordinated control behavior of multiple vehicles which is the major goal of the European Project GREX. It is shown that the relative positioning problem is solvable when dead reckoning data are combined with the mutual range data measured via acoustic modems. Therefore, the limited capability of the acoustic communication channel has to be considered when developing a solution algorithm. A simple concept is achieved by implementing a recursive variant of a trilateration technique by means of an extended Kalman filter.

Path Planning for Cooperative Line Of Sight Target Tracking of Heterogeneous Unmanned Marine Vehicle Teams

Abstract In this paper we suggest a procedure to perform path planning for cooperative target pursuit, performed by a heterogeneous team of unmanned marine vehicles. This work was performed in the framework of the research project GREX (IST-Project-No. 035223) which aims for the realization of several mission scenarios including cooperative marine vehicles. We will describe the algorithms for the team leader to calculate new paths for all team members online and demonstrate the results in a computer simulation.