Thor I. Fossen

Norwegian University of Science and Technology | NTNU · Department of Engineering Cybernetics

Handbook of Marine Craft Hydrodynamics and Motion Control is an extensive study of the latest research in hydrodynamics, guidance, navigation, and control systems for marine craft. The text establishes how the implementation of mathematical models and modern control theory can be used for simulation and verification of control systems, decision-sup...

Parametric Resonance in Dynamical Systems discusses the phenomenon of parametric resonance and its occurrence in mechanical systems, vehicles, motorcycles, aircraft and marine craft, along micro-electro-mechanical systems. The contributors provides an introduction to the root causes of this phenomenon and its mathematical equivalent, the Mathieu-Hi...

A comprehensive and extensive study of the latest research in control systems for marine vehicles. Demonstrates how the implementation of mathematical models and modern control theory can reduce fuel consumption and improve reliability and performance. Coverage includes ocean vehicle modeling, environmental disturbances, the dynamics and stability...

This brief presents a novel nonlinear adaptive line-of-sight (ALOS) guidance law for path following, compensating for drift forces due to wind, waves, and ocean currents. The ALOS guidance law is proven to have uniform semiglobal exponential stability (USGES) properties during straight-line path following at constant speed. The ALOS guidance law pe...

This study investigates the potential capability of a relatively new and unexplored signal-based approach for ship-board wave estimation. The approach uses the phase-time-path-differences (PTPDs) from an array of shipboard sensors to uniquely resolve the wave propagation direction and wave number. We derive a kinematic PTPD model accounting for for...

This article is intended as a tutorial to assist engineers who want to develop and implement low-cost underwater vehicle inertial navigation systems (INS) aided by time-delayed hydroacoustic position measurements. A discrete-time unit quaternion error-state Kalman filter (ESKF) is used for sensor fusion. The ESKF is implemented as a feedback algori...

Ship maneuvering in narrow harbor environments requires accurate navigation data to operate safely. Since Global Navigation Satellite Systems (GNSS) can be unreliable and inaccurate in such environments, other aiding techniques should be used for increased redundancy and reliability. To this end, we present a GNSS-free sensor suite consisting of vi...

Dynamic positioning (DP) is one of the key technologies towards ship autonomy. Ships in DP mode use thruster devices to maintain position and perform low-speed maneuvering. The motion controller issues force requests according to the measured ship state and motion objectives. These requests must be translated into individual thruster commands. Due...

We consider encrypted guidance systems for straight-line path following. With cloud-computing technology, we can outsource computations in guidance systems to third-party providers, increasing scalability and enabling guidance-as-a-service. However, by remotely hosting a conventional guidance system on third-party infrastructure, we leak informatio...

The launch and recovery of equipment such as remotely operated vehicles (ROVs) is a critical task that defines the operability limits of many marine operations. This paper considers the analysis of control systems that are designed to maximize the operability limits for launch and recovery of a ROV from a small unmanned surface vessel (USV). We use...

Docking is a safety-critical operation for autonomous surface vehicles and requires highly accurate navigation signals. Since Global Navigation Satellite Systems (GNSS) can be unreliable and inaccurate in urban environments, other sensors should be considered for increased redundancy and reliability. To this end, we present a low-cost visual-inerti...

The overall goal of the article is to derive a kinematic model for vehicle path-following systems, where the pitch and yaw angles (θ, ψ) together with the surge velocity u can be treated as control inputs. Then the outer control loop can be designed as a nonlinear path-following guidance law. At the same time, the inner control loops can be stabi...

There exist several collision avoidance algorithms for autonomous ships. But the majority of them do not utilize information about other ships' intentions, except for observed position and velocity. As the attention for large-sized autonomous ships to be used in logistics is growing, autonomous ships will need to collaborate and negotiate with othe...

Unlike common marine vessels, wave-propelled vehicles cannot directly control their speed, but rely instead on the forces exerted by the environment to navigate as intended. The unique navigation capabilities of such vehicles motivate the study of control solutions that adapt the vehicle heading to the prevailing environmental conditions and ensure...

This paper presents an independent stereo-vision based positioning system for docking operations. The low-cost system consists of an object detector and different 3D reconstruction techniques. To address the challenge of robust detections in an unstructured and complex outdoor environment, a learning-based object detection model is proposed. The sy...

Driven by advances in information and communication technologies, an increasing number of industries embrace unmanned and autonomous vehicles for services, such as public transportation, shipping, mapping, and remote surveillance. Unfortunately, these vehicles are vulnerable to passive and active cyber‐physical attacks that can be used for industri...

A common approach for finding the direction of ocean waves is to use the phase-time-path-differences (PTPDs) between a static array of various types of sensors mounted on either the sea surface or seabed. However, some practical drawbacks of such arrays are that they tend to be expensive, difficult to install, and fixed in location. We show that th...

Path-following control systems for ships can be designed using both heading and course angle autopilots in conjunction with a proportional line-of-sight (LOS) guidance law. Ships are usually equipped with a gyrocompass from a safety perspective since magnetic compasses are susceptible to magnetic disturbances. Unfortunately, the gyrocompass is an e...

Small USVs are usually equipped with a low-cost navigation sensor suite consisting of a global navigation satellite system (GNSS) receiver and a magnetic compass. Unfortunately, the magnetic compass is highly susceptible to electromagnetic disturbances. Hence, it should not be used in safety-critical autopilot systems. A gyrocompass, however, is hi...

An ever-increasing number of autonomous vehicles use bandwidth-greedy sensors such as cameras and LiDARs to sense and act to the world around us. Unfortunately, signal transmission in vehicles is vulnerable to passive and active cyber-physical attacks that may result in loss of intellectual property, or worse yet, the loss of control of a vehicle,...

This paper presents nonlinear, singularity-free autopilot designs for multivariable reduced-attitude control of fixed-wing aircraft. To control roll and pitch angles, we employ vector coordinates constrained to the unit two-sphere and that are independent of the yaw/heading angle. The angular velocity projected onto this vector is enforced to satis...

This paper focuses on a novel feedback linearization control (FLC) law based on a self-learning disturbance observer (SLDO) to counteract mismatched uncertainties. The FLC based on BNDO (FLC-BNDO) demonstrates robust control performance only against mismatched time-invariant uncertainties while the FLC based on SLDO (FLC-SLDO) demonstrates robust c...

Artificial intelligence is an enabling technology for autonomous surface vehicles, with methods such as evolutionary algorithms, artificial potential fields, fast marching methods, and many others becoming increasingly popular for solving problems such as path planning and collision avoidance. However, there currently is no unified way to evaluate...

Autonomous surface vehicles are gaining increasing attention worldwide due to the potential benefits of improving safety and efficiency. This has raised the interest in developing methods for path planning that can reduce the risk of collisions, groundings, and stranding accidents at sea, as well as costs and time expenditure. In this paper, we rev...

Knowledge of the amplitude and frequency of sea waves is useful to characterize the sea state, and increases the situational awareness as perceived by unmanned marine crafts. The ability to adapt navigation control parameters according to the current sea state is an essential feature for vehicles whose motion is mainly governed by environmental for...

In this paper a multiple object detection, recognition, and tracking system for unmanned aerial vehicles (UAVs) has been studied. The system can be implemented on any UAVs platform, with the main requirement being that the UAV has a suitable onboard computational unit and a camera. It is intended to be used in a maritime object tracking system fram...

Conventional dynamic positioning (DP) systems on larger ships compensate primarily for slowly time-varying environmental forces. In doing so, they use wave filtering to prevent the DP from compensating for the first-order wave motions. This reduces wear and tear of the thruster and machinery systems. In the case of smaller autonomous vessels, the o...

While automatic controllers are frequently used during transit operations and low-speed maneuvering of ships, ship operators typically perform docking maneuvers. This task is more or less challenging depending on factors such as local environment disturbances, number of nearby vessels, and the speed of the ship as it docks. This paper proposes a to...

Autonomous surface vehicles are gaining increasing attention worldwide due to the potential benefits of improving safety and efficiency. This has raised the interest in developing methods for path planning that can reduce the risk of collisions, groundings, and stranding accidents at sea, as well as costs and time expenditure. In this paper, we rev...

Artificial intelligence is an enabling technology for autonomous surface vehicles, with methods such as evolutionary algorithms, artificial potential fields, fast marching methods, and many others becoming increasingly popular for solving problems such as path planning and collision avoidance. However, there currently is no unified way to evaluate...

A uniform semiglobal exponential stability (USGES) proof for a time-varying vector field guidance law used for path-following control of vehicles is presented. A sliding mode control is introduced for heading autopilot design and Lyapunov methods are used to derive the control law. The equilibrium point of the autopilot error dynamics is proven to...

In this article, we suggest that a strapdown inertial navigation system based on microelectromechanical system (MEMS) inertial sensors is a useful addition to a vessel with dynamic positioning (DP). We conduct full-scale experiments with MEMS inertial sensors on board a DP vessel operating off the Norwegian coast. The vessel operates in different s...

As an alternative to reduced-attitude control of fixed-wing unmanned aerial vehicles using roll and pitch angles, we propose to use a global representation that evolves on the two-sphere. The representation of reduced attitude is invariant to rotations about the inertial gravity axis, which makes it well suited for banked turn maneuvers. With the r...

This paper presents a method for estimating the air data parameters for a small fixed-wing, unmanned aerial vehicle (UAV) using an arrangement of low-cost MEMS-based pressure sensors embedded in the surface of the UAV. The pressure measurements are used in a machine learning (ML) model to estimate the angle of attack (AOA), sideslip angle (SSA), an...

This article considers the problem of constructing an observer for estimating position, velocity, attitude, underwater wave speed, rate sensor bias, and accelerometer bias that has both proven stability and close-to-optimal performance with respect to noise. The observer takes pseudorange, pseudorange difference, depth, and inertial measurements as...

This paper presents two Kalman filter approaches for correcting air data systems providing relative velocity measurements with an additive constant or slowly time-varying bias for fixed-wing unmanned aerial vehicles (UAVs). In addition to the air data system, both estimators rely on a standard sensor suite consisting of a GNSS receiver, an IMU, and...

When a ship experiences a loss of position reference systems, its navigation system typically enters a mode known as dead reckoning (DR) to maintain an estimate of its position. Commercial systems perform this task using a state estimator that includes mathematical model knowledge. Such a model is nontrivial to derive and needs tuning if the vessel...

Navigating in environments where GNSS- and magnetometer measurements are unreliable can lead to a significant decrease in state estimation accuracy. The use of supplementary measurements, either from optical sensors or otherwise, could enhance the state estimates notably even when at low quality. Using inertial navigation corrected by a multiplicat...

In this paper, we develop a cooperative control algorithm for a group of multirotor unmanned aerial vehicles (UAVs) transporting a suspended payload of unknown mass. In addition, the vehicles are subjected to unknown environmental disturbances in the form of wind. The control structure is analyzed using Lyapunov theory, and both numerical simulatio...

This paper addresses the problem of ship motion estimation using live data from Automatic Identification Systems (AIS) and extended Kalman filter (EKF) design. AIS data are transmitted from ships globally and a very-high frequency (VHF) AIS receiver picks up the signals as coded ASCII characters in a format specified by the National Marine Electron...

This paper addresses the problem of ship motion estimation using live data from Automatic Identification Systems (AIS). A globally exponentially stable observer for visualization and motion prediction of ships has been designed. Instead of using the extended Kalman filter (EKF) to deal with the kinematic nonlinearities the eXogenous Kalman Filter (...

This paper presents four vision-based tracking system architectures for marine surface objects using a fixed-wing unmanned aerial vehicle (UAV) with a thermal camera mounted in a pan/tilt gimbal. The tracking systems estimate the position and velocity of an object in the North-East (NE) plane, and differ in how the measurement models are defined. T...

This paper presents a novel attitude estimator called the multiplicative exogenous Kalman filter. The estimator inherits the stability properties of a nonlinear observer and the near-optimal steady-state performance of the linearized Kalman filter for estimation in nonlinear systems. The multiplicative exogenous Kalman filter is derived in detail,...

This paper focuses on a novel feedback linearization control (FLC) law based on a self‐learning disturbance observer (SLDO) to counteract mismatched uncertainties. The FLC based on BNDO (FLC‐BNDO) demonstrates robust control performance only against mismatched time‐invariant uncertainties while the FLC based on SLDO (FLC‐SLDO) demonstrates robust c...

This paper considers the problem of constructing a filter for estimating attitude and rate-sensor bias, that has both proven stability and close-to-optimal performance with respect to noise. The filter is based on measuring the difference in time of arrival for signals sent from three or more known, fixed positions to two or more receivers on the v...

A modular nonlinear observer is considered for tightly coupled integration of inertial measurements with global satellite measurements. A real-time-kinematic (RTK) approach is utilized where the rover and base station measure pseudoranges, carrier-phase, and carrier-phase derived Doppler, to be used in a dual receiver configuration. The modular obs...

When trying to capture the heaving motion of a marine vessel in waves, conventional position references such as global navigation satellite systems fall short in many cases. Because of design and satellite geometry, the vertical position measurement is typically inferior in both accuracy and precision compared to its horizontal counterparts. For ai...

Dynamic Positioning (DP) of ships is a control mode that seeks to maintain a specific position (stationkeeping) or perform low-speed maneuvers. In this paper, a static Neural Network (NN) is proposed for control allocation of an over-actuated ship. The thruster force and commands are measured during a trial run of the simulated vessel to gather dat...

This article presents a novel recovery method for fixed-wing unmanned aerial vehicles (UAVs), aimed at enabling operations from marine vessels. Instead of using the conventional method of using a fixed net on the ship deck, we propose to suspend a net under two cooperative multirotor UAVs. While keeping their relative formation, the multirotor UAVs...

We present two alternative methods for fault detection and isolation (FDI) with redundant Microelectromechanical system (MEMS) inertial measurement units (IMUs) in inertial navigation systems (INS) based on nonlinear observers (NLOs). The first alternative is based on the parity space method, while the second is expanded with quaternion-based avera...

In this paper, we consider the problem of trajectory tracking of a multirotor Unmanned Aerial Vehicle carrying a suspended payload. The movement of the suspended payload influences the dynamics of the multirotor, which must be appropriately handled by the controller to achieve satisfactory tracking results. We derive a mathematical model of the int...

In this paper, exponentially stable nonlinear observers for the estimation of position, velocity, specific force, attitude, and gyro bias of a fixed-wing unmanned aerial vehicle (UAV) are proposed. The sensor suite consists of an inertial measurement unit, a global navigation satellite system receiver, a camera, an altimeter, and, possibly, auxilia...

This paper presents a passivity based formation control strategy for multiple unmanned aerial vehicles (UAVs) cooperatively carrying a suspended load. The control strategy we propose consists of an internal feedback control law for each UAV and a formation control law that regulates the relative position between each UAV. We show that under this co...

In this paper we present an alternative configuration of sensors, position and heading reference systems for dynamically positioned (DP) vessels. The approach uses a sensor structure based on low-cost inertial measurements units (IMUs), satisfying fault tolerance against single-point failures that is at the essence of the IMO guidelines for both DP...

Navigation is a term with broad usage in everyday life and can mean the act of moving, moving through an unknown environment, ascertaining a craft's position, or even browsing on the Internet. Originally, the term meant the skill of sailing a ship, in particular steering and maneuvering, and is derived from the Latin words navis and agere, meaning...

This chapter aims at applying a recently proposed estimator, called eXogenous Kalman Filter (XKF), to the navigation of a fixed-wing unmanned aerial vehicle (UAV) using inertial sensors, GNSS, and optical flow calculated from a camera . The proposed system is a cascade interconnection between a globally exponentially stable (GES) nonlinear observer...

This paper develops a vision-based tracking system in unmanned aerial vehicles based on thermal images . The tracking system are tailored toward objects at sea and consists of three main modules that are independent. The first module is an object detection algorithm that uses image analysis techniques to detect marine vessels in thermal images and...

This paper develops a vision-based tracking system in unmanned aerial vehicles based on thermal images . The tracking system are tailored toward objects at sea and consists of three main modules that are independent. The first module is an object detection algorithm that uses image analysis techniques to detect marine vessels in thermal images and...

There exist numerous navigation solutions already implemented into various navigation systems. Depending on the vehicle in which the navigation system is used, it can be distinguished in most cases among; navigation, tactical, and commercial grade categories of such systems. The core of these systems is formed by inertial sensors, i.e. acceleromete...

Global navigation satellite system (GNSS) receivers suffer from an internal time-delay of up to several hundred milliseconds leading to a degeneration of position accuracy in high-dynamic systems. With the increasing interest in GNSS navigation, handling of time-delays will be vital in high accuracy applications with high velocity and fast dynamics...

A modular nonlinear observer for inertial navigation aided by pseudo-range measurements is designed and analyzed. The attitude observer is based on a recent nonlinear complementary filter that uses magnetometer and accelerometer vector measurements to correct the quaternion attitude estimate driven by gyro measurements, including gyro bias estimati...

This edited volume includes thoroughly collected on sensing and control for autonomous vehicles. Guidance, navigation and motion control systems for autonomous vehicles are increasingly important in land-based, marine and aerial operations. Autonomous underwater vehicles may be used for pipeline inspection, light intervention work, underwater surv...

Dead reckoning capabilities are vital in ship navigation if position and heading references are unrealizable or lost. In safety critical marine operations such as dynamic positioning, the International Maritime Organization and classification societies require that the vessel possesses dead reckoning capabilities and position reference redundancy....

We conduct full-scale experimental validation and comparison of three different nonlinear attitude observers, two of them with inherent heave estimation, in two different operational scenarios encountered by an offshore vessel in the North Sea. Two different micro-electro-mechanical inertial measurement units are the primary sensors for driving the...

This paper presents an exponentially stable nonlinear wind velocity observer for fixed-wing unmanned aerial vehicles (UAVs). The observer uses a model of the aircraft combined with a GNSS-aided inertial navigation system (INS). The INS uses an attitude observer together with a pitot static probe measuring dynamic pressure in the longitudinal direct...

This chapter is the study of state estimators for robust navigation. Navigation of vehicles is a vast field with multiple decades of research. The main aim is to estimate position, linear velocity, and attitude (PVA) under all dynamics, motions, and conditions via data fusion. The state estimation problem will be considered from two different persp...

The estimation of a vehicle's position and velocity based on measurements of pseudoranges and range-rates is a nonlinear filtering problem. We utilize a linearized Kalman filter with global convergence that avoids divergence because the local model linearization is not based on the linearized Kalman filter's own estimates. Instead, the linearizatio...

This paperpresentsa vision-aided uniformly semiglobally exponentially stable nonlinear observer for estimation of attitude, gyro bias, position, velocity, and specific force of a fixed-wing unmanned aerial vehicle, using measurements from an inertial measurement unit, a global navigation satellite system receiver, and computer vision. The computer...

This paper presents a vision-based tracking system for marine surface objects utilizing images captured in a fixed-wing unmanned aerial vehicle (UAV) with a retractable pan/tilt gimbal. A formula for calculating the North-East velocities of objects detected in the images is derived. The formula utilizes optical flow (OF) and compensates for the UAV...

Ship-based Unmanned Aerial Vehicle (UAV) operations represent an important field of research which enables a large variety of mission types. Most of these operations demand a high level of endurance which normally requires the use of a fixed-wing UAV. Traditionally, a net located on the ship deck is used for recovering the fixed-wing UAV. However,...